Organophosphorus Chemistry (SPR Organophosphorus Chemistry (RSC)) (v. 3)

A Specialist Periodical Report Organophosphorus Chemistry Volume 3 A Review of the Literature Published between July ...

Author: S. Trippett

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A Specialist Periodical Report

Organophosphorus Chemistry Volume 3

A Review of the Literature Published between July 1970 and June 1971

Senior Reporter

S. Trippett, Department of Chemisfry, The University, Leicester Reporters R. S. Davidson, The University, Leicester

N. K. Hamer, Cambridge University D. W. Hutchinson, Universify of Warwick R. Keat, Glasgow Universify J. A. Miller, University of Dondee

D. J. H. Smith, The University, Leicesfer J. C. Tebby, North Staffordshire Polytechnic 6. J. Walker, Queen's Universify of Belfasf

ISBN : 0 85186 026 5 @ Copyright 1972

The Chemical Society Burlington House, London, W I V OBN

Organic fornrulue composed b y Wrighr’s Symbolser merhod

I’riiitcd in Grrat Brituin by John Wright uiitl . Y i m l.td, n t The Stonebridge Press, Bristol HS4 5 N / J

Foreword

This third volume continues the pattern set by its predecessors and covers the literature available to the Reporters from July, 1970, to June, 1971. The highlight for many organophosphorus chemists during this period was the EUCHEM Conference organised by Professor Leopold Horner and held at Schloss Elmau in March-April, 1971. Apart from the thriving state of organophosphorus chemistry, the chief impression gained by many of the participants was of a general erosion of the simple mechanistic pictures adequate in this field over the past ten years. The advent of pseudorotation, the precise details of which threaten to become controversial, and the increasing volume of data which cannot be accommodated within the framework of existing ideas promise exciting, if occasionally confusing, developments for report in subsequent volumes. S. T.

Contents

Chapter 1 Phosphines and Phosphonium Salts By D. J. H. Smith

I Phosphines 1 Preparation A From Halogenophosphine and Organometallic Reagent B From Metallated Phosphines C By Reduction D Miscellaneous

1

2 Reactions A Nucleophilic Attack on Carbon (i) Activated Olefins (ii) Activated Acetylenes (iii) Carbonyls (iv) Miscellaneous B Nucleophilic Attack on Halogen C Nucleophilic Attack on Other Atoms D Miscellaneous

5 5 5 6

7 8 9 12 14

I I Phosphonium Salts I Preparation

16

2 Reactions A Alkaline Hydrolysis B Additions to Vinylphosphonium Salts C Miscellaneous

20 20 24 25

III Phosphorins and Phospholes 1 Phosphorins A Preparation B Structure C Reactions

26 26 27

2 Phospholes

28

27

vi

Contents

Chapter 2 Quinquecovalent Phosphorus Compounds By S. Trippett 1 Introduction

30

2 Acyclic

30

3 Four-membered

31

4 Five-membered A 2,2’-Bi pheny l ylenep hosp horanes B 1,3,2-Dioxaphospholens C 1,3,2-Oxazaphospholans D Miscellaneous

32 32 34

5 Six-membered

39

35 37

Chapter 3 Halogenophosphines and Related Compounds By J. A. Miller 1 Halogenophosphines A Preparation B Reactions (i) Nucleophilic Attack at Phosphorus (ii) Biphilic Reactions with Dienes or Carbonyl Compounds (iii) Miscellaneous

40

2 Halogenophosphoranes A Preparation and Structure B Reactions

46 46

3 Phosphines containing a P-X

52

Bond (X = Si, Ge, or Sn)

40 42 42 44 45

48

Chapter 4 Phosphine Oxides and Sulphides By J. A. Miller 1 Bonding and Structure

54

2 Preparation A Using Organometallic Reagents B By Hydrolysis Reactions C By Oxidation D Miscellaneous

55 55 57 59 61

Contents

vii 3 Reactions

A Nucleophilic Reactions of the P=O Group B Electrophilic Reactions of the P=O and P=S Groups C Reactions not involving the P=O and P=S Groups

61 61

62 64

Chapter 5 Tervalent Phosphorus Acids By B. J. Walker 1 Introduction

68

2 Phosphorous Acid and its Derivatives A Nucleophilic Reactions (i) Attack on Saturated Carbon (ii) Attack on Unsaturated Carbon (iii) Attack on Nitrogen (iv) Attack on Oxygen (v) Attack on Halogen B Electrophilic Reactions C Rearrangements D Cyclic Esters of Phosphorous Acid E Miscellaneous Reactions

68 68 68 71 80 81 83 84 86 86 90

3 Phosphonous Acid and its Derivatives

91

Chapter 6 Quinquevalent Phosphorus Acids By N. K. Hamer 1 Phosphoric Acid and its Derivatives A Synthetic Methods B Solvolyses of Phosphoric Acid Derivatives C Reactions

95 95 1 00

105

2 Phosphonic and Phosphinic Acids and Derivatives A Synthetic Methods B Solvolyses of Phosphonic and Phosphinic Esters C Reactions of Phosphonic and Phosphinic Acid Derivatives

I08 108 11 1

3 Miscellaneous

I19

I15

...

Cuntenrs

Vlll

Chapter 7 Phosphates and Phosphonates of Biochemical Interest By D. W . Hutchinson 1 Mono-, Oligo-, and Poly-nucleotides A Mononucleotides B Nucleoside Polyphosphates C Oligo- and Poly-nucleotides D Nucleoside Thiophosphates E Physical Methods and Analytical Techniques

122 122 127 129 132 133

2 Coenzymes and Cofactors A Phosphoenol Pyruvate B Nicotinamide and Flavin Coenzymes C Nucleoside Diphosphate Sugars D Coenzyme A

134 134 135 136 137

3 Naturally Occurring Phosphonic Acids A Aminophosphonic Acids B Phosphonomycin

137 137 138

4 0xidat ive Phosphory lat ion

139

5 Sugar Phosphates and Phosphonates A Pentoses B Hexoses

141 141 142

6 Inositol Phosphates and Phospholipids A Inositol Phosphates B Phospholipids

144 144 144

7 Enzymology

145

8 Other Compounds of Biochemical Interest

147

Chapter 8 Ylides and Related Compounds By S. Trippett 1 Methylenephosphoranes A Preparation B Reactions (i) Halides (ii) Carbonyls (i ii) M iscell aneous

150 150 152 152 156 163

2 Phosphoranes of Special Interest

166

Contents

ix 3 Selected Applications of the Wittig Olefin Synthesis A Natural Products (i) Carotenoids

(ii) Prostaglandins (iii) Miscellaneous B Macrocyclics C Miscelianeous

170 170 170 173 173 176 178

4 Synthetic Applications of Phosphonate Carbanions

180

5. Ylide Aspects of Iminophosphoranes

183

Chapter 9 Phosphazenes By R. Keat 1 Introduction

187

2 Synthesis of Acyclic Phosphazenes A From Amides and Phosphorus(v) Halides B From Cyano-compounds and Phosphorus(v) Halides C From Azides and Phosphorus(rr1) Compounds D Other Methods

187 187 190 191 194

3 Properties of Acyclic Phosphazenes A Halogeno-derivatives B Aryl Derivatives C Other Derivatives

198 198 203 207

4 Synthesis of Cyclic Phosphazenes

210

5 Properties of Cyclic Phosphazenes A Amino-derivatives €3 Alkoxy- and Aryloxy-derivatives C Alkyl and Aryl Derivatives D Pseudohalogeno-derivatives

213 21 3 21 8 22 1 224

6 Polymeric Phosphazenes

224

7 Molecular Structures of Phosphazenes Determined by X-Ray Diffraction Methods

226

Chapter 10 Radical, Photochemical, and Deoxygenation Reactions By R. S. Davidson 1 Radical and Photochemical Reactions

230

Contents

X

2 Desulphurization and Deoxygenation Reactions

238

Chapter 11 Physical Methods By J. C. Tebby 1 Nuclear Magnetic Resonance Spectroscopy A Chemical Shifts and Shielding Effects B Studies of Equilibria and Reactions C Pseudorotation D Restricted Rotation E Inversion, Non-equivalence, and Configuration F Spin-Spin Coupling (i) JPP and JPM (ii) JPF (iii) Jpc (iv) JPH (v) JP(',II (4JPO(*,,H,JPN(,,,H, and JPNPH G Relaxation Times, Paramagnetic Effects, and N.Q.R. Studies

248 248 254 255 258 259 262 262 263 263 263 264 267

2 Electron Spin Resonance Spectroscopy

269

3 Vibrational Spectroscopy A Band Assignments and Structural Elucidation B Stereochemical Aspects C Studies of Bonding

270 270 27 I 27 3

4 Microwave Spectroscopy

275

5 Electronic Spectroscopy

276

6 Rotation and Refraction

278

7 Diffraction

279

8 Dipole Moments, Polarography, and Other Electrical Properties

283

9 Mass Spectrometry

285

268

10 pK and Thermochemical Studies

288

I1 Surface Properties

290

12 Radiochemical and Miscellaneous Studies

292

Author Index

293

A bbre viations

AIBN DBU DCC DMF DMSO g.1.c. HMPT PPi n.q.r. TCNE THF t.1.c.

bisazoisobu tyroni tri le

1,5-diazabicyclo[5,4,O]undec-5-en dicyclohexylcarbodi-imide NN-d i met hylformamide di met hyl sulphoxide gas--liqui d chromatography hex a met h y I p h 0 sp ho r ic t ria mi de inorganic pyrophosphate nuclear quadrupole resonance tetracyanoet hylene tetrahydrofuran thin-layer chromatography

1

Phosphines and Phosphonium Salts BY D. J. H. SMITH

PART 1: Phosphines

1 Preparation A. From

Halogenophosphine and Organometallic Reagent.--Mesitylmagnesium bromide reacts with chlorodiethylphosphine and dichloroethylphosphine at - 10 "C in THF to yield mesityldiethylphosphine and dimesitylethylphosphine respectively.' Bis(dipheny1phosphino)methyl-lithium, from methyl-lithium and bis(diphenylphosphino)methane,gave the compound (1) with chlorodiphenylphosphine., (Ph,P),CHLi

+ Ph,PCl

-

(Ph,P),CH (1)

The six isomeric tris(methylthienyl)phosphines, e.g. (2), have been prepared by the reaction of methylthienyl-lithium derivatives with phosphorus t r i b r ~ m i d e . ~ Arylaluminium compounds (3) are obtained from the reaction of diphenylphosphine and triarylalumini~rns.~ The trimethylstannyl grouping in the phosphine (4) is replaced by diphenylphosphino upon reaction with chlorodiphenylphosphine.6

(Me,Sn),P (4)

'

+ 2Ph,PCI

-

Me,SnCl

+ (Ph,P),P

L. K. Il'ina, K. V. Karvanov, E. N. Karpova, A. I. Bokanov, and B. I. Stepanov, Zhur. obshchei Khim., 1970,40, 581 (Chem. Abs., 1970,73, 25 576). K. Issleib and H. P. Abicht, J . prakt. Chem., 1970, 312, 456 (Chern. Abs., 1970, 73, 109 844). H. J. Jakobsen, Acta Chem. Scund., 1970, 24, 2661. D. Giurgiu, I. Popescu, A. Ciobanu, M. Bostan, N. Voiculescu, and L. Roman, Rev. Roumaine Chim., 1970, 15, 1581 (Chem. Abs., 1971, 74, 53 893). H. Schumann, A. Roth, and 0. Stelzet, J . Organometallic Chem., 1970, 24, 183.

2

Orgumphosphorus Chemistry

A number of (polyhalogenoary1)phosphines have been synthesized by the addition of a chlorophosphine to a polyhalogenoaryl-lithium compound or a Grignard reagent.8 A complex reaction takes place when dichlorobis(tripheny1phosphine)nickel ( 5 ) is treated with excess methylmagnesium bromide in ether.' Detectable amounts of benzene, toluene, and biphenyl are formed, together with mixed phosphines. Nickel appears to be necessary for the substitution reaction since triphenylphosphine alone does not react with the Grignard reagent .

+ MeMgBr

(Ph,P):NiCI,

----+

PhH

(5)

+ PhMe + Ph, + Ph,MeP + PhMe,P

Good yields of phosphines have been obtained* by the simultaneous addition of an organolithium compound and an alkyl chloride to a solution of a cyclopolyphosphane (6). (R'P),

+ nLiR2 + nR3Cl

(6)

-

nR1R2R3P+ nLiCl

R', R2, R3 = alkyl, R3Si, R,Ge, or R3Sn

B. From Metallated Phosphines.--Lithium diphenylphosphide and ethylene oxide produce (7), which when added to chlorodibutyl- or chlorodiphenylphosphine yields 2-diphenylp hosphinoethyl p hosphini tes (8). @

Ph2PLi

+

/

\

H,C-CH,

--+ Ph,PCH2CH20Li

Ph,PCH,CH,OPR, (8)

R

= Ph,

n-C,H,

8-Quinolylphosphines have been prepared from the reaction of 8-chloroquinoline and potassium diphenylphosphide, or the quinolyllithium derivative and a chlorophosphine.1° A phenyl group can be cleaved, with lithium, from alkylphenylphosphines to give lithium alkylphenylphosphides, which with diphenylvinyl-

* lo

S. S. Dua, R. C. Edmondson, and H. Giiman, J . Organometallic Chem., 1970,24, 703. M. L. H. Green, M. J. Smith, H . Felkin, and G. Swierczewski, Chem. Comm., 1971,158. M. Schmidt and W.-R. Neeff, Angew. Chern. Znternat. Edn., 1970, 9, 807. S. 0. Grim, A. W. Yankowsky, and W. L. Briggs, Chem. and Ind., 1971, 575. K. Issleib and M. Haffendorn, 2. anorg. Chem., 1970, 376, 79 (Chem. A h . , 1970, 73, 77 333).

Phosphines and Phosphonium Salts

3

phosphine l1 produce good yields of the expected unsymmetrical di tertiary phosphines (9). RPhPCH2CH2PPh, (9; R = alkyl)

The ditertiary phosphines (1 l), prepared from the corresponding alkyl chloride and lithium diphenylphosphide react with sodium in liquid ammonia to give the phosphines (12).

Phosphides add to the double bond of mp-unsaturated carbonyl compounds l 3 to give the phosphines (13). PhCH=CHCOR1

+ MPHR2

----+

R2PHCHPhCH2COR1 (13)

R1 = Me, Ph; R2 = Ph, C,H,, The organometallic phenylphosphines (14) are obtained from the reaction of lithium phenylphosphide and Group IV chlorides.14 PhPHLi

+ MsMCI

-

PhPHM(Me), (14)

M = Si, Ge, or Sn

Phosphine and lithium aluminium hydride form lithium tetraphosphinoaluminate (1 5 ) which reacts with trimethyltin chloride Is to give the phosphine (16). 4Me3SnC1

+ LiAKPH,), (15)

-

LiCl

+ AICI, + 4Me3SnPH, (16)

The reaction of dipotassium phosphide with dichlorodiphenylsilane and diphenylgermanium dichloride l6 yields the dimers (1 7) and trimers (1 8). 3-Chloroprop-1-yne reacts with sodium diphenylphosphide in liquid ammonia to give diphenylprop-1-ynylphosphine (1 9). However, when the addition is carried out in THF a mixture of the prop-2-ynylphosphine l1 la

lS

S. 0. Grim, R. P. Molends, and R. L. Keiter, Chem. andInd., 1970, 1378. K. Sommer, 2. anorg. Chern., 1970, 376, 37 (Chem. Abs., 1970,73, 77 326). K. Issleib and P. V. Malotki, J . prakr. Chem., 1970, 312, 366 (Chern. Abs., 1970, 73, 77 337).

l4

l5 lo

P. G. Harrison, S. E. Ulrich, and J. J. Zuckerman, J . Amer. Chem. Soc., 1971, 93, 2307.

A. D. Norman, J . Organometallic Chem., 1971, 28, 81. H. Schumann and H. Benda, Chem. Ber., 1971, 104, 333.

4

Organophosphorus Chemistry

(20), the allenylphosphine (21), and the prop-1-ynylphosphine (19) is obtained. If excess diphenylphosphide is avoided, pure diphenylprop-2ynylphosphine (20) is the product. These products presumably arise from an S Nreaction ~ followed by a prototropic rearrangement.”

TI

Diferrocenylphenylphosphine and ferrocenyldiphenylphosphine have been prepared by a modified procedure.ln C. By Reduction.---The cyclic secondary phosphines phospholan and phosphorinan have been prepared by reduction of the corresponding chlorophosphines with lithium aluminium hydride.le The reduction of optically active methylphenyl-n-propylphosphine sulphide with lithium aluminium hydride proceeds with 100% retention,20 whereas the reaction of phosphine oxides with lithium aluminium hydride leads to racemization.21

2o

W. Hewertson, I. C. Taylor, and S. Trippett, J . Chetn. SOC.(C), 1970, 1835. C. E. Sullivan and W. E. McEwen, Org. Prep. Proced., 1970, 2, 157. K. Sommer, 2. anorg. Chem., 1970, 379, 56. R. Luckenbach, Tetrahedron Letters, 197 I , 2 177. P. D. Henson, K . Naumann, and K . Mislow. J . Atuer. Chem. Suc., 1969, 91, 5645.


5

D. Miscellaneous.- The base-catalysed addition of diphenylphosphine to excess vinyl isocyanide 22 gave (22). However, the reaction of phenylPh,PH

+ CH,=CHNC

THE'

Ph2PCH,CH,NC (22)

phosphine with excess vinyl isocyanide gave the azaphosphole (23). The addition of phenylphosphine to 2,6-cycloheptadien-l-oneat 140 "C gave a mixture of (24) and (25) which can be separated by sublimation or di~tillation.~~ rn-Nitro-substituted triaryl- and alkyldiaryl-phosphines can be prepared by the nitration of methoxymethylphosphonium salts with nitronium tetrafluoroborate.24

2 Reactions A. Nucleophilic Attack on Carbon. -(i) Activated OZeJins. A study of triarylphosphine-catalysed dimerization of acrylonitrile to 2-methyleneglutaronitrile (26) and 1,4-dicyano-l-butene (27) has established a balance between phosphine nucleophilicity and protolytic strength of the solvent.25 The reaction of methyl vinyl ketone with triphenylphosphine in triethylsilanol gave only 3-methylene-2,6-heptadienone(28). CH,=CHCN

Ar3P

NCC(: CH,)CH,CH2CN

+ NCCH=CHCH,CH,CN (27)

(26)

MeCOCH :CH, 22 2a *4

EtsPiOH Ph3P +

MeCOC(: CH2)CH2CH,COCH: (28)

R. B. King and A . Efraty, J. Amer. Cheni. Soc., 1971, 93, 564. Y.Kashman and 0. Awerbouch, Tetrahedron, 1970, 26, 4213. G. P. Schiemenz and K. Rohlk, Chetn. Ber., 1971, 104, 1219. J. D. McClure, J. Org. Cheni., 1970, 35, 3045.

Organophosphorus Chemistry 0-

0

4-Methylene-2,6-di-t-butyl-2,5-cyclohexadien-l-one reacts with tributylphosphine 28 in benzene to form an isolable betaine (29). For the reaction of tetramethyldiphosphine with butadiene see Chapter 10, Section 1. (ii) Acfivafed Acefylenes. The reaction of triphenylphosphine with phenylacetylene has been investigated in more The rearrangement has been shown to proceed via the vinylphosphonium salt (30).

Ph,P

+

HCiCPh

+

H,O ---+

+

OH-

Ph,P*CH:CHPh (30) OH I Ph3PCH:C H Ph

T i In a similar rearrangement dibenzophosphorin oxides (3 1) have been prepared from the reaction of dibenzophosph(rr1)oles with methyl propiolate.28 Some ring expansion occurs even when R = benzyl, presumably because of the difficulty of putting benzyl in an apical position in the intermediate phosphorane. The reaction of triphenylphosphine with an excess of dimethyl acetylenedicarboxylate2g gives not only the phosph(v)ole (32) but also a cyclopen tenylidenephosphorane (33). 26 27

28 29

W. H. Starnes and J. J. Lauff, J . Org. Chem., 1970, 35, 1978. E. M. Richards and J. C. Tebby, J . Chem. SOC.(C), 1971, 1059. E. M. Richards and J. C. Tebby, J . Chem. SOC.(C), 1971, 1064. N. E. Waite, J . C. Tebby, R. S. Ward, M. A. Shaw, and D. H. Williams, J . Chem. SOC. (C), 1971, 1620.

a-0


\

7

+ HCiC-CO,Me +

/

H,O +

I

/ \

R

R

R

=

CH:CHCO,Me

k-'

Me, Ph, or PhCHz

OH-

dH2c O4 / K

(31)

Ph3P

+

Me0,C - CO.,Me Me0,CC i CCO,Me---+ McO,C (&Me \ p PI1

+

C0,Mc M e 0 2 C p M ' Me0,C 0

PI1*

PPh, (33) 20%

(32) 40";

(iii) Carbonyls. Bifluorenylidenes (34) are formed from tributylphosphine

and fluorenones in the absence of solvent. When the reaction is carried out in a solvent having abstractable hydrogens a complex mixture is produced. Tetraphenylcyclopentadienone and tributylphosphine gave (35) and a hydrocarbon. These reactions are thought to proceed through carbene or carbenoid intermediate^.^^

X PI1

=

-

H or Br Ph

Q1o PI1 -

(34) 4(%

Ph

+ Bu3P --+ Ph

- Ph

Ph - Ph

[Itci + Ph Ph-

C58H40

Ph

( 3 5 ) 28:; ( - )-Methylphenyl-n-propylphosphinereacts with halogenoketones 31 to give ketophosphonium salts (36) with retention of configuration at phos8o 91

I. J. Borowitz, M. Anschel, and P. D. Readio, J . Org. Chern., 1971, 36, 553. I. J. Borowitz, K. C. Kirby, P. E. Rusek, and W. E. R . Casper, J . Org. Chern., 1971,

36, 88.

8


phorus, and enol phosphonium salts (37) with inversion of configuration at phosphorus, indicating that the former result from S N displacement ~ of halide ion by the phosphine and the latter from phosphine attack on halogen followed by recombination of the resulting ion pair. t

c1

PI piperylene > chloroprene. These data support the previous suggestion that attack on the diene is an electrophilic process. The formation of the phosphoranes (23) in the preparation of the phosphonites (24) has been shown l4 to be due to two processes: firstly, the acid-catalysed disproportionation of the phosphonites to give (23) and cyclopolyphosphines; and secondly, the remarkable base-catalysed reaction of the phosphonites with catechol to give (23) and hydrogen. l1 la l3

l4

Y. Ogata and M. Yamashita, J . Amer. Chem. SOC.,1970, 92, 4670. F. Ramirez, J. Bauer, and C. D. Telefus, J. Anier. Chem. SOC.,1970, 92, 6935. N. A. Razumova and F. V. Bagrov, J. Gen. Chem. (U.S.S.R.), 1970, 40, 1232. M. Wieber and W. R. Hoos, Monarsh., 1970, 101, 776.

Quinquecoualent Phosphorus Cornpoitiids

35

(96 - 9 8 O 3

(22)

C. 1,3,2-Oxazaphospholans.-The diastereoisomeric spirophosphoranes (25) and (26) obtained from ( - )-ephedrine and trisdimethylaminophosphine are in equilibrium in benzene their relative proportions varying with temperature. That this equilibration, which requires epimerization at l5

J.-F. Brazier, J. Ferekh, A. Mufioz, and R. Wolf, Compr. rend., 1971, 272, C , 1521

36


phosphorus, is not due to an intermolecular transfer of ephedrine residues was shown by a study of the diastereoisomers (27) and (28) containing one ( - )-ephedrine and one $-( )-ephedrine.

+

Ph

MeN-P’ I\NMe O d M e

MeN-P’ (“Me

Ph

O A M e

The secondary products formed in the synthesis of spirophosphoranes from trisdimethylaminophosphine and p-amino-alcohols have been identified l6 as the betaines (29), formed from the spirophosphoranes as shown.

A stable adduct (31) has been obtained from the cyclic phosphorodiamidite (30) and benziL6 J. Ferekh, A. Mufioz, J.-F. Brazier, and R. Wolf, Compt. rend., 1971, 272, C, 797.

Quinquecooalent Phosphorus Compounds

+

[:>P*NMe,

37

'(--((

NMe,

N-PJph

Me

PhCO-COPh -+

Me (30)

Ph (31)

D. Miscellaneous.-Low yields of the spirophosphoranes (34) were obtained1' on heating the phosphorane (32) with the aziridines (33). Stable phosphoranes have been obtained from phenanthraquinone monoimine (35) and trialkyl phosphites,18 and from 2-chlorotropone (36) and ~ 1 i d e s . lIn ~ the latter reaction cyanomethylenetriphenylphosphorane gave instead the betaine (37). CH.,.CH,.NH.P(:O)(OR):!

€4

[0,P ,P\ ) +(RO)*P(:0)--N3 0

0

-=[ I

O\ / O 0,p, 0

170'C

(33)

-J

(34) ( 1 9-26%)

(32)

a''+ (35)

Ph,P:CHR

1

--+

0

R

(36)

=

H, Me, C0,Et

CN

(37) N. P. Grechkin and L. N. Grishina, Bull. Acad. Sci. U.S.S.R., 1970, 1549. lUM. M . Sidky and M. F. Zayed, Tetrahedron Letters, 1971, 2313. l 8 1. Kawamoto, Y . Sugimura, and N. Soma, unpublished data quoted in I. Kawamoto, T. Hata, Y . Kishida, and C. Tamura, Tetrahedron Letters, 1971, 2417.

l7

38


The 1:l-adducts obtained 2o from the ethylene phosphonothioites (38; R = Ph or But) with diacetyl, benzylideneacetylacetone, and phenanthraquinone readily eliminate ethylene sulphide to give the corresponding phosphonate or phosphinate esters. The benzylideneacetylacetone adduct of (38; R = But) contained the two diastereoisomers (39) and (40) which, on elimination of ethylene sulphide at 100 "C,gave isomeric phosphinates.

I

I

H. Ph O......p,~COMe

But'

0

Me

The equilibrium between the conformers (42a) and (42b) of the 1 :1-adduct of dimethyl t-butylphosphonite (41) and benzylideneacetyl-

acetone is so far to one side that the n.m.r. spectrum of the adduct does not vary with temperature.20 The phosphoranes (43) have been obtained from (41), and the corresponding phenylphosphonite, and methylenedeoxybenzoin. In both adducts pseudorotation between (43a) and (43b) became slow on the n.m.r. time scale below - 10 "C.

ButP(OMe),

+

PhCH:C(COMe),

---+

Me0 MeO... I I! Bu'-u;hoMe

(41) MC

(42a) Me0 M e 0... I

Me0

R4T>Ph 0

0

Ph

(43a)

Me0 Bu !.. I ',' P-' PI1 MeO' I

3FoMc Mc

R

=

Ph or But

(43W

A. P. Stewart and S . Trippett, Chem. Comm., 1970, 1279.

Qiririquecovalerit Phosphorits Comportrids

39

A full account has appeared 21 of the reactions of the 2 : 1 fluorenetriet hyl phosphite adducts on heating and with acetonitrile. 5 Six-membered

The bicyclic phosphites (44) and (46) did not react with benzil, even at 60 "C for 20 days.6 With diacetyl at 60 "C for 8 days the l:2-adducts, e.g. (45) from (44), were obtained. The reluctance of these bicyclic phosphites to form stable phosphoranes is remarkable as their geometries appear to be ideal for this purpose. The lH and 19F n.m.r. spectra of the phosphorane (47) indicate rapid positional exchange of the ligands attached to phosphorus.22 This has been quoted 23 as evidence for a (2 + 3)-turnstile process of ligand reorganization, the normal Berry (1 + 4)-pseudorotation being held to be impossible in (47) because of increased strain. Details of this work are awaited with interest .

21

1. J. Borowitz, M. Anschel, and P. D. Readio, J . Org. Chem., 1971, 36, 553.

22

F. Ramirez, S. Pfohl, E. A. Tsolis, I. Ugi, D. Marquarding, P. Gillespie, and P. Hoff-

as

mann, unpublished data quoted in ref. 23. I. Ugi and F. Ramirez, Angew. Chern. Internat. Ecln., 1970, 9, 725.

3 Halogenophosphines and Related Compounds ~~

BY J. A. MILLER

1 Halogenophosphines A comprehensive review of the preparation, reactions, and n.m.r. spectra of phosphorus-fluorine compounds has appeared.l This year's literature has been notable for the first detailed applications of ab initio SCF-MO calculations to the problems of bonding in halogenophosphines and their Comparison of the results of such theoretical calculations with experimental data obtained from photoelectron spectra shows a good correlation in the case of phosphorus trichloride and phosphoryl chloride,2 and of phosphorus trifluoride and its borane c ~ m p l e x . ~ A. Preparation.-Halogen displacement reactions have been used to prepare a number of new aminofluorophosphines. Aminodifluorophosphine ( 1 j has been prepared for the first time, from either bromodifluorophosphine % or chlorodifluorophosphine,6and ammonia. Studies of its n.m.r. spectrum have been made (see Chapter 11). The related NNdifluoroaminodifluorophosphine (2j has been prepared,8 from difluoroiodophosphine, and found to be explosive. Two syntheses of N-alkyl-aminodifluorophosphines have been reported,6* one of which was complicated by the subsequent formation of the phosphorane (3) and the bis-(Nalky1amino)fluorophosphine (4).

a

* 6

7

G . I. Drozd, Russ. Cheni. Rev., 1970, 39, 1. I. H . Hillier and V. R Saunders, Chem. Comm., 1970, 1510. I. H. Hillier, J. C . Marriott, V. R. Saunders, M. J . Ware, D. R. Lloyd, and N. Lynaugh, Chem. Comm., 1970, 1586. D. W. H . Rankin, J . Chem. SUC.( A ) , 1971, 783. J. E. Smith and K. Cohn,J. Amer. C'hem. Suc., 1970, 92, 6185. J . E. Smith, R . Steen, and K . Cohn, J . Amer. Chem. Soc., 1970, 92, 6359. J . S. Harman and D. W. A. Sharp, J . Chem. SOC.( A ) , 1970, 1935.

Halogenophosphines and Related Compounds KNH,

+

PF, --+

RNHPF,

41

+ RAH,.HF,

(3)

t-Butyldifluorophosphine ( 5 ) and di-t-butylfluorophosphine (6) have been prepared from their respective chlorides by different routes,a determined by the ease with which the chloride forms a phosphorane. The mono-t-butyl compound, unlike simple alkyl and aryl a n a l o g ~ e s is , ~stable to disproportionation. Two general routes to 1 -chlorophospholens have been reported,1° and the synthetic utility of these compounds has been developed. Both routes involve the formation of mixtures of 1-chloro-A2-phospholens (7) and 1-chloro-A3-phospholens (8). Grignard reactions of t-pentylmagnesium chloride with phosphorus trichloride have been used I1 to prepare dichloro-t-pentylphosphine (9) and chlorodi-t-pentylphosphine (lo), although the second stage requires more vigorous conditions than the first. RutPCI, 1- SbF, ___> Bu'PF,

Bu',PCI

+

F-

---+

ButzPF

[ , , +) ........-

Ph,P

I

J

PCI3

" lo

+

PetMgC1

PetPCI2

Pe"MgC1

M . Fild and R . Schmutzler, J . Chent. SOC.( A ) , 1970, 2359. H. G . Ang and R. Schmutzler, J . Chem. SOC.,( A ) 1969, 702. D. K. Myers and L. D. Quin, J . Org. Chem., 1971, 36, 1285. P. C. Crofts and D. M . Parker, J . Chem. SOC.(C), 1970, 2529.

Pet,PC1

42


B. Reactions.-(i) Nucleophilic Attack at Phosphorus. A reinvestigation l2 of the reaction between phosphorus trichloride and t-butylbenzene in the presence of aluminium chloride has shown that the product after hydrolysis is the substituted phosphinic acid (1 l), and not the expected l 3 phosphonic acid (1 2). Bis(N-alky1amino)phosphines have been reported l4 to attack chlorodiphenylphosphine with nitrogen, in the presence of a base, to give bis(N-alkyl-N-dipheny1phosphinoamino)phenylphosphines(1 3). In (1 3), the terminal phosphorus atoms are more reactive14than the central one towards sulphur and towards alkyl halides.

PCI,

(12)

Ph,PCl

-I- PhP(NHR),

EbN ,NRPPh, + PhP, NRPPh,

The product l5 of the base-catalysed reaction between t-butyldichlorophosphine and ethyl alcohol is the expected l6 diethyl t-butylphosphoni te (14), and this quaternizes readily with methyl iodide. An efficient synthesis of carbamic acid halides (1 5 ) , from NN-dialkylformamides, phosphorus trichloride, and thionyl chloride, is reported,” although a full rationalization of the reaction has not been presented. The reactions 18 of phosphorus trichloride with oxetans provide an interesting contrast to those with epoxides, reported several years ago, as shown below. I t appears that the epoxide ring opens at the more highly substituted carbon, to give (16), whereas the comparable oxetan ring opens at the less substituted of the carbon atoms joined to oxygen, to produce (17). A la 13

l4 l6

l6 1’

1’’

R. Brooks and C. A. Bunton, J . Org. Chem., 1970, 35, 2642. G. M. Kosolapoff, J . Amer. Chem. SOC.,1954, 76, 3222. R. Keat, W. Sim, and D. S. Payne, J . Chem. SOC.( A ) , 1970, 2715. P. C . Crofts and D. M . Parker, J . Chem. SOC.(C), 1970, 2342. P. C. Crofts and D. M . Parker, J . Chem. SOC.( C ) , 1970, 332. N . Schindler and W. Ploger, Chem. Bet-., 1971, 104, 969. B. A. Arbuzov, L. Z . Nikonova, 0. N . Nuretdinova, and V. V. Pomazanov, Iire,sr. Akad. Naiik S . S . S . R . , Ser. khirn., 1970, 1426. N. I. Shuikin and I. F. Bel’skii, Zhirr. obshchei. Khint., 1959, 29, 2973.

43

Halogenophosphines and Related Compoundp

possible explanation is that, in the epoxide case, ring-opening precedes carbon-chlorine bond formation, while the same steps in the oxetan reaction are more nearly concerted (see Section 2B). ButP(OEt) (14)

KZNCHO

+

PCl,

+

-

0 II

RZN-C-CI

SOCI,

Me &Me

+

I

PClj --+ Cl,P.O.CH.CH,-CH,CI

Two papers have appeared on the reactions of halogenophosphines with tervalent phosphorus compounds. In a detailed study 2o of the reactions at 20 "C of a range of tertiary phosphines with phosphorus trichloride, dichlorophenylphosphine, and chlorodiphenylphosphine, it has been shown that, in general, 1 : 1 adducts are formed, provided that the tertiary phosphine is a good nucleophile. With diphenylchlorophosphine, for example, an adduct (18) is formed with dimethylphenylphosphine,but not with diphenylmethylphosphine, although the relative importance of steric and electronic factors remains to be established. The related reactions of phosphorus trichloride and of dichlorophenylphosphine are much more complex, and the initial crystalline products are not amenable to analysis. The reactions at 280 "C of a similar system have been shown 21 to lead to halogen exchange, e.g. the conversion of (19) to (20). Ph2PCl

+

20 "C

Me,PPh

2o

F. Kamirez and E. A. Tsolis, J .

a1

K. Sommer, Z . anorg.

Arnpr..

/

Ph2P$MeZPh el

C'hrm. Suc., 1970, 92, 7553.

Chem., 1970, 376, 37.

44


(ii) Biphilic Reactions with Dienes or Carbonyl Compounds. Stereochemical details have appeared 22 of the reactions between substituted 1,3-dienes and halogenophosphines, such as dichloromethylphosphine (21 a) and dibromophenylphosphine (21 b). In general, both cis- and trans-adducts are formed, and they are not interconvertible via quinquecovalent intermediates. The conversion of these adducts to A3-phospholens or to A3-phospholen- 1-oxides produces cis-trans mixtures. Acetone reacts 23 with neat dichlorophenylphosphine or dichloroethylphosphine to give 3,3,5-trimethyl-A4-1,2-oxaphospholen-2-oxides(22a, b), and other simple methyl ketones have been shown 24 to undergo analogous reactions. Although a rationalization of this process has not been presented, it has been demonstrated 24 that diacetone alcohol with dichloroethylphosphine gives (22b), and that mesityl oxide also reacts 25 similarly with phosphorus trichloride, to give (23). In reactions25 with a number of dichlorophosphines, mesityl oxide forms acyclic products (24), which appear to be the result of ring-opening of the oxides (22), or of their precursors.

170 Thus, in the magnesium(i1)-catalysed system P - 0 bond fission is the predominant reaction, while C - 0 bond fission is the major process in the calcium(r1)-catalysed rea~ti0n.l~'It may be that the nature of the acetyl phosphate-metal ion complex has an important bearing on this reaction, and an intermediate such as (86) would favour C - 0 cleavage while (87) might be expected to favour P - 0 cleavage in a bimolecular ~ e a c t i 0 n . l ~ ~ 4-

(86)

(87)

Acetate kinase is phosphorylated by acetyl phosphate and it has been shown that the phosphoenzyme can synthesise ATP from ADP, and acetyl phosphate from The mode of decomposition of carbamyl phosphate in aqueous solution is pH dependent and can proceed with either the production of ammonia and carbon dioxide (equation l), or cyanate (equation 2).'74 No cyanate could be detected during the hydrolysis Nl12C0,P0,H2 NCO-

+ HI'O,= + Ii,O

(2)

of carbamyl phosphate by acyl phosphatase, suggesting that the hydrolysis proceeds as in equation 1, unless an unusually rapid decomposition of cyanate occurs in this ~eacti0n.l'~ Interest in 'presqualene pyropho~phate'l~~ continues and it is claimed 177 that the structure (88) assigned178 to a squalene precursor is incorrect. Presqualene pyrophosphate has been shown to contain a cyclopropyl ring ~~~ (89),177and both (89) and its parent alcohol have been s y n t h e ~ i s e d . 'le0 Mechanisms for the conversion of (89) into squalene have been published.181pla2 C. H. Ostreich and M . M. Jones, Biochemistry, 1966, 5 , 2926. P. J. Briggs, D. P. N. Satchell, and G. F. White, J. Chem. SOC.( B ) , 1970, 1008. 171 J. P. Klinman and D. Samuel, Biochemistry, 1971, 10, 2126. 172 F. J. Farrell, W. A. Kjellstrom, and T. G. Spiro, Science, 1969, 164, 320. l i Y R. S. Anthony and L. B. Spector, J. Biol. Chem., 1970, 245, 6739. 17' C. M. Allen, jun., and M. E. Jones, Biochemistry, 1964, 3, 1238. 176 D. Diederich, G. Ramponi, and S . Grisolia, F.E.B.S. Letters, 1971, 15, 30. 176 H. C. Rilling, J. Biol. Chem., 1966, 241, 3233. W. W. Epstein and H. C. Rilling, J. Biol. Chem., 1970, 245, 4597. 17* G. Popjik, J. Edmond, K. Clifford, and V. Williams, J. Biol. Chem., 1969, 244, 1897. 17B L. J. AItman, R. C. Kowerski, and H. C. Rilling, J. Amer. Chem. SOC., 1971, 93, 1782. l n 0 R. M. Coates and W. H. Robinson, J. Amer. Chem. SOC., 1971, 93, 1785. 181 H. C. Rilling, C. D. Poulter, W. W. Epstein, and B. Larsen, J. Amer. Chem. SOC., 1971.93, 1783. l R 2 E. E. van Tamelen and M. A. Schwartz. J. Amer. Chem. Soc., 1971, 93, 1780. lB0 lio

148


RC H, C ( h.1 e 1=C I I C H,C H, C H-

/

0

04p’\ H0

c-C H I< \

o /

H y T i O p Z O G I 1,

0

‘r)-oij \\ 0

(88) where K gcranyl

c Mc, // c Mc / 14

Cf1,R

CH,R

‘

(89)

The substrate specificity of farnesyl pyrophosphate synthetase has been studied using 3-methyl-2-alkenyl pyrophosphates (90) as m0de1s.l~~When (90) bears a large side-chain (i.e. R = CIHg),the reaction with isopentenyl pyrophosphate ceases after the formation of (91) and this reaction has been

(90)

(91)

used to synthesise 16,16’-bisnorgeranylgeranyl pyrophosphate.ls4 The acid-catalysed hydrolyses of isopentenyl phosphate and pyrophosphate proceed with P-0 bond fission; on the other hand, hydrolysis of the allylic dimethyl ally1 pyrophosphate occurs with C-0 Neopterin cyclic phosphate (92) has been isolated as an intermediate in the biosynthesis of pteridines from GTP in Comamonas.186 Tracer studies show that the phosphoryl group in (92) originates from the

(92)

a-phosphorus atom in GTP. Neopterin triphosphate which is synthesised from GTP in E. coli does not appear to be an intermediate in Comamonas. Clindamycin (93; R = H), an antibiotic obtained by chlorinating lincomycin, is converted by a species of Streptomyces into inactive phosphoruscontaining These have been shown to be nucleoside 5’-phosphates derived from adenosine, cytidine, guanosine, and uridine. K. Ogura, T. Nishino, T. Koyama, and S. Seto, J . Amer. Chem. SOC.,1970, 92, 6036. T. Nishino, K. Ogura, and S. Seto, J . Amer. Chem. SOC.,1971, 93, 794. B. K. Tidd, J . Chem. SOC.(B), 1971, 1168. 18a J. Cone and G. Guroff, J . Biol. Chem., 1971, 246, 979. lB7 A. D. Argoudelis and J . H . Coats, J . Amer. Chem. SOC.,1971, 93, 534.

lB3

lB4

Phosphates and Phosphonates of Biochemical Interest

149

OH (93)

where R

==

ribonucleosidc 5'-phosphoryl or 14

A new, heat-stable, coenzyme concerned with methyl group transfer has been isolated from Methunobacterium.188 The coenzyme, which is involved in transmethylation reactions prior to methane formation by the organism, contains phosphorus and has a U.V. absorption at 260 nm, suggesting that it may be a nucleotide. The presence of inorganic polyphosphate in electron-dense particulate structures of M. Iuteus has been demonstrated by 31Pn.m.r.,le9 confirming an earlier observation based on chemical 180

B. C. McBride and R. S. Wolfe, Biochemistry, 1971, 10, 2317. T. Glonek, M. Lunde, M. Mudgett, and T. C. Myers, Arch. Biochem. Biophys., 1971,

loo

I. Friedberg and G. Avigad, J . Bacteriol., 1968, 96, 544.

18a

142, 508.

6

8 Ylides and Related Compounds BY S. TRIPPETT

1 Methylenephosphoranes A. Preparation.--The first reverse Wittig olefin synthesis has been rep0rted.l Triphenylphosphine oxide and dicyanoacetylene at 160 "C gave the stable ylide (1 ; 78%); the reaction was reversed at 300 "C. No comparable reaction was observed with a variety of other activated acetylenes but triphenylarsine oxide gave the corresponding stable arsoranes with dicyanoacetylene ( - 70 "C), methyl propiolate, hexafluorobut-2-yne, dimethyl acetylene dicarboxylate, and ethyl phenylpropiolate (1 30 "C). Ph3P0

+ NC*CIC*CN

300 "C p

Ph3P:C(CN)*CO*CN

160 'C:

(1)

Phosphonium fluorides have been used in olefin synthesis without additional base, the fluoride anion being sufficiently strong a base to remove the a-proton from the salts (2; R = Ar or COR') in acetonitrile. Ph,P+*CH,R F-

f- Ph3P:C H R p-N02'C6I14*C3

(2)

p-NO,*C,H,*CH:CHR (31-86%)

Salt-free ylides have been prepared from phosphonium chlorides and bromides by treatment with sodamide in refluxing THF. The sodium halide precipitates and is removed by filtration, Allylidene- and benzylidenetrimethylphosphoranes have been obtained as low melting distillable solids from the phosphonium chlorides and butyl-lithium in ether. The allylidenephosphorane on standing at room temperature slowly decomposed to give methylenetrimethylphosphorane. Previous difficulties in the generation of the ylide from the spiro-phosphonium salt (3) have been overcome by treating the salt with sodium hydride in DMSO in the presence of a carbonyl compound or by refluxing 1 2

s 4

a

E. Ciganek, J . Org. Chem., 1970, 35, 1725. G . P. Schiemenz, J. Becker, and J . Stockigt, Chem. Ber., 1970, 103, 2077. R. Koster, D. SimiC, and M. A. Grassberger, Annalen, 1970, 739, 211. W. Malisch, D. Rankin, and H. Schmidbauer, Cheni. Ber., 1971, 104, 145. N. Ya. Derkach and A. V. Kirsanov, J . Gen. Chern. (U.S.S.R.), 1970, 40, 1411.

YIides arid Related Compoirrids

151

a solution of the salt in t-butanol with benzaldehyde and potassium t-butoxide.8 The resulting unsaturated phosphine oxides were obtained in 18-23% yield.

(3)

( 1 8-2373

The formation of the azo-ylides ( 5 ) from the chlorohydrazones (4) as shown may have involved addition of triphenylphosphine to intermediate 1,3-dipoles or directly to the chlorohydra~ones.~ PhsP

+ RCCl:N*NHPh + Et3N

r:'.,:

+

Ph,P: CR*N:NPh

(4)

(5)

R = COMe, CO,Et, or p-NO,*C,H,

Alkylation of the metallated bis(triphenylphosphiny1)methane (6) with benzyl or methyl chlorides occurred on phosphorus to give the ylides (7). That from benzyl chloride reacted with chlorodiphenylphosphine to give the stable ylide (8).

The dangers of using alkyl-lithiums to generate highly reactive ylides are illustrated by the use of butyl-lithium to prepare the chloromethylene ylide (9). When the resulting solution was treated with the aldehyde (10) the olefins (1 1) and (12) were obtained, in addition to the expected olefin. Presumably the ylides leading to (1 1) and (12) were formed via the quinquecovalent phosphorane (13); migration of a group from phosphorus to the methylene with expulsion of chloride ion would give the salts corresponding to these ylides. For the formation of ylides from triphenylphosphine with dimethyl acetylene dicarboxylate and with halonitroalkenes see Chapter I , Section 2. B. D. Cuddy, J. C. F. Murray, and B. J. Walker, Tetrahedron Letters, 1971, 2397. V. V. Kosovtsev, V. N. Chistokletov, and A. A. Petrov, J . Gen. Chem. (W.S.S.R.), 1970.40, 21 16.

K. Isslieb and H. P. Abicht, J . prakt. Chem., 1970, 312, 456. G . W. Pilling and F. Sondheimer, J . Amer. Chern. SOC.,1971, 93, 1970.

a'",


152

CTH

Ph,P. + CH,CI BuLi THF, - 70 C

CHO

>

a

C

X

+

H

CH:CHCI

CH:CH Ph

,

Ph P :C HC 1 (9)

+ BuPh,kH,Ph

(I3)

CI-

B. Reactions.-(i) Halides. Whereas ylides are alkylated in the normal way on treatment with a-bromo- or a-iodo-esters, quite different reactions occur with a-fluoro- and a-chloro-acetates. When salt-free ylides were refluxed in benzene with ethyl fluoroacetate or trifluoroacetate l o normal Wittig olefin synthesis took place with the carbonyls of the ester groups to give vinyl ethers, e.g. (14). On the other hand, methyl chloroacetate with Ph3P:CHPh

+ CF3*COzEt

-

PhCH:C(OEt)CF, (14) (78%)

+ Ph,PO

ylides gave l1 only the cyclopropane (1 5 ) , presumably via the anion (16). This anion was partly trapped as the cyclopropane (17) by carrying out the reaction in the presence of an excess of methyl crotonate. Ph:,P:CHR

+ CICH,CO,Me

+ Ph,{;.CH,K

+ CICHC0,Mc (16)

CICH,CO,Me

+ (16) -+

MeO,C*CHCI-CH,-CO,Mc Ph,,P: CHR

C0,Mc ( 1 6 ) hle02C~ c-- h.lcO,C.CH:CH.CO,Mc C0,Mc (15) M e CO,Me

C0,Me

(17) lo

l1

H. J. Bestmann, H. Dornauer, and K. Rostock, Chem. Ber., 1970, 103, 2011. H. J. Bestmann, H. Dornauer, and K. Rostock, Annalen, 1970, 735, 52.

Ylides and Related Compounds

I53

The 1,Sdiene (1 9) was obtained l2 from the salt (1 8) by alkylation of the ylide with ally1 bromide and reduction of the resulting salt with lithium in ethylamine.

The reaction of ylides with phosphorus(1rr) halides has been extended l 3 to the ylides (Me,N),Me,-,P:CH,, n = 1, 2 , or 3. Alkylation of the resulting stabilized ylides (20) with methyl iodide took place on the tervalent phosphorus, e.g. (Me,N),P: CH,

+ Et,PCl

----+

(Me,N),P: CH-PEt, (20) McI

(Me2N)3P:CHOP+-MeEt,I -

Full accounts have appeared of the exchange of trimethylsilyl for chlorosilyl groups on treatment of trimethylsilylylides with chlorosilanes l4 and of the stabilizing effects of the simple silyl (SiH,) group on ~ 1 i d e s . I ~ The exchange process involves nucleophilic attack of the ylide on the silicon of the chlorosilane, e.g.

Me,,P:C(SiMc,),

+ Me,SiCI,

{

SiMe,

I -+Mc,P-C-SiMegI 13

fSiMe3

-C1

J-

,SiMe, hle,P:C, SiMc,CI

+ Me3SiC1 l2 I:’

K . E. Harding and K. A. Parker, Tetrahedron Lerrers, 1971, 1633; see E. H. Axelrod, G. M. Molne, and E. E. van Tamelen, J . Amer. Chem. Soc., 1970, 92, 2139. K. Isslieb and M. Lischewski, J . prclkr. Chem., 1970, 312, 135. H. Schmidbauer and W. Malisch, Chem. Ber., 1971, 104, 150. H. Schmidbauer and W. Malisch, Chern. Ber., 1970, 103, 3007.

154

0rgnnophosphorids Chemistry

Silyl migrations readily occur in silylated ylides to give the ylides of optimum stability.16 Thus, deprotonation of the salts (21) and (23) gave the ylides (22) and (24), respectively. Intermolecular silyl transfers, from one ylide (or the corresponding phosphonium salt) to another, also lead to maximum stabilization. Silyl transfer does not occur l7 in the product (26) from methylenetrimethylphosphorane and the chlorodisilane (25), pre-

Sihlc:,

(32)

(21 1 hl c t

I

hlc31’--C‘ t 4

-

--

tI

- f

I Sihlc,,

(23)

n sumably for the same steric reasons which lead to the formation of (26) rather than the expected am-disilylated ylide. The same phosphorane with the dichlorodisilane (27) gave the cyclic bis-ylide (28), while the cyclic ylide (29) was obtained from (27) and trimethylsilylmethylenetrimethylphosphorane followed by butyl-lithium. 3 hlc, P C H ,

+ 2 Mc,Si.SiMe,C‘I (25)

C, -+ Mc,P,

H *, Si M c2-Si hl e:, CH-SiMc,-SiMe:,

+

(26) 2 Mc.,f’I (’I

PMe, I1 C hle,Si’ ‘SiMe, 6 Me,P:CH, + 2 C1Mc2Si-SiMc,CI -+ I I Me,Si, ,SiMe, (27) C I1

PMe, (28) l7

H. Schmidbauer and W. Malisch, Chem. Ber., 1970,103, 3448. H . Schmidbauer and W. Vornberger, Angew. Chent. Internat. Edn., 1970, 9, 737.

Ylides arid Related Compounds

155

(I)

hle,P:CH.SiMe,

(27)

(11) BuLi

1 “ ‘SiMe,

+ Me,P Nc,

I S i Me,

I SiMc, (?9)

A full account has appeared l* of the reactions of the ester phosphoranes (30; R3 = H) with acyl chlorides. Equimolecular proportions gave the salts (3 1) from which 15-ketoesters were obtained on electrolytic reduction. A 2 : 1 excess of phosphorane gave the allenic esters (32), presumably via the betaines (33).

The absolute configurations of carboxylic acids can be determined l 9 from the sign of rotation of the phosphonium salt precipitated when the corresponding acyl chlorides are treated with the optically active ylide (34) in THF. It is found that the sign of the specific rotation of the precipitated salt agrees with the sign of the chirality product x when the absolute configuration of the acyl chloride is as in (35). The chirality product is given by the equation:

where the ligand constants, A, are assigned as described by Ugi and Ruch.20

‘Lo

H. J. Bestmann, G . Graf, H . Hartung, S. Kolewa, and E. Vilsmaier, Chern. Ber., 1970, 103, 2194. H. J. Bestmann, H. Scholz, and E. Kranz, Amgrw. Chem. Iiiternat. Edn., 1970, 9, 796. E. Ruch and I . Ugi, Topics Stereochem., 1969, 4, 99.


156

Me

M t:

I 2 Ph--P=CH.Pti 1 Pr (34)

+ R’K2RR:’C.COCI

7 I1F

I Ptl--P=CPti.CO.CK’K’RR“ I

Pr

hf c

Pr

(35)

(ii) Carbonyls. The stereochemistry of the Wittig olefin synthesis has been reviewed.21 trans-Stereoselective olefin synthesis via /3-oxido-ylides is possible only in the presence of soluble lithium salts.2a Protonation of p-oxido-ylides prepared from salt-free ylides leads to mixtures of erythroand threo-betaines and hence to mixtures of cis- and trans-olefins. Large concentrations of halide ions, preferably iodide, favour the formation of trans-stil bene from benzaldehyde and benzyltriphenylphosphoniunl halides in methanol with methoxide as base, whereas large concentrations of methoxide ions slightly favour formation of the ~ i s - i s o r n e r . ~These ~ effects have been explained by the preferential solvation of P+ by halide ions, leading to greater reversi bility of betaine formation. Methoxide ions, on the other hand, are preferentially solvated by methanol. The quality of phenyl-lithium used to generate ylides can have a pronounced effect on the stereochemistry of olefin synthesis. In the reactions of the ylide (36) with the aldehydes (37) cis-olefins were obtained using a phenyl-lithium solution containing one equivalent of total base while trans-olefins resulted from the use of an amount of this solution containing one equivalent of genuine phenyl-lithium together with six equivalents of other, unspecified, base.24

M . Schlosser, Topics Stereochem., 1970, 5 , 1. x M. Schlosser, K.-F. Christmann, and A. Piskala, Cheni. Ber., 1970, 103, 2814. z y T. Bottin-Strzalko, J . Seyden-Penne, and B. Tchoubar, Compt. rend., 1971,272, C,778. a 4 E. J. Reist and P. H. Christie, J . Org. Chem,, 1970, 35, 4127. z1

157

Yiides and Related Compounds

A polymer containing side-chain benzylphosphonium residues has been prepared and used in olefin synthesis.25 A suspension in THF was treated with base and benzaldehyde overnight and the polymeric phosphine oxide was then removed by filtration. The yields of stilbenes, 40% with potassium t-butoxide and 60% with sodium hydride, were not improved by using an excess of base or of aldehyde. The aldehyde group of laevulinic aldehyde reacted preferentially with the ester phosphorane (38),26 while the 2-acetyl groups of the benzofurans (39) were selectively methylenated 27 with methylenetriphenylphosphorane. The aldehyde group was protected as the dimethylacetal in the synthesis 28 of the steroidal a-methylene-aldehyde (40).

R

=

ti, OH. o r OMe

R

2

OH (73",,)

(39)

CH(OMe),

CHO

CO

C:CH,

I

I

(40)

The carbonyl group of the keto-acid (41) is remarkably unreactive2@ towards methylenetriphenylphosphorane. Only 10% of unsaturated acid was obtained using a large excess of reagent in DMSO at 58 "Cfor several days.

(41) 25

2R 27 2H

28

(43)

F. Camps, J. Castells, J. Font, and F. Vela, Tetrahedron Letters, 1971, 1715. A. J. Birch, J. E. T. Corrie, and G. S. R. Subba Rao, Austral. J . Chem., 1970, 23, 1811. J. A. Elix, Austral. J . Chem., 1971, 24, 93. W. Haede, W. Fritsch, K. Radschett, U. Stache, and H. Ruschig, Annalen, 1970,741,92. D. F. MacSweeney and R. Ramage, Tetrahedron, 1971,27, 1481 ; F. Kido, H. Uda, and A. Yoshikoshi, Chem. Comm., 1969, 1335.

Organophosphoriis C hernist ry

158

Scrambling of tritium was observed 30 in reactions of the bisphosphonium salt (42) with geranylacetone in t-butanol containing potassium t-butoxide. Recovered ketone had incorporated tritium and the resulting squalene had a maximum of 32.8% of scrambling. Scrambling in methylenation of the a-deuterioketone (43) was avoided 31 by using the ether (EtOCH2CH2)20 as solvent and butyl-lithium as base. The isomerization observed in the methylenation of cis-a-decalones has been turned to good advantage. Mixtures of cis- and trans-isomers of the a-decalones (44) 32 and (46) 33 gave only the trans-decalins (45) and (47).

(47)

(46)

Quantitative yields of allenes were obtained 34 from keten and the stable phosphoranes (48). Addition of similar phosphoranes occurred 35 at the p-position of the allenic ketones (49) to give the phosphoranes (50). The compound (50; R1 = COPh) eliminated phosphine oxide under the conditions of the reaction to give the acetylene (51).

+

c l r 2c:12

Ph,P:CR’R2 CH,:C:O + R1R2C:C: CH, (48; R1 = H or Me; R2 = CN, COR, or C0,Et)

2H-Pyran-2-ones were obtained 36 in low yield on heating p-diketones, e.g. (52), with the ester phosphorane (53) under severe conditions. In refluxing benzene the cyclopropenones (54) with the phosphoranes ( 5 5 ) gave 37 triphenylphosphine and the pyran-2-ones (58) (50%). At room so

D. H. R. Barton, G. Mellows, D. A. Widdowson, and J. J. Wright, J . Chem. Suc. (C), 1971, 1142.

81

3a 33 34

36 30

37

T. B. Malloy, jun., R. M. Hedges, and F. Fisher, J . Org. Chem., 1970, 35, 4256. J. W. Huffman and M. L. Mole, Tetrahedron Letters, 1971, 501. C. H . Heathcock and R . Ratcliffe, J. Amer. Chern. Soc., 1971, 93, 1746. Z. Hamlet and W. D. Barker, Syrrrhesis, 1970, 2, 543. G. Buono, G. Peiffer, and A. Guillemonat, Cumpt. rend., 1970, 271, C , 937. A. K. Soerensen and N. A. Klitgaard, Acta Chem. Scand., 1970, 24, 343. T. Eicher, E. v. Angerer, and A.-M. Hansen, Annafen, 1971, 746, 102.


159

temperature (54; R1 = Ph) and (55; R2 = OMe) also gave the normal Wittig product (57). The methylenecyclobutanes (60) were formed from the same phosphoranes and the methylenecyclopropene (59). The formation of the pyran-2-ones may involve the intermediate cyclobutenones (56) as shown.

5%

160

Organophosphorirs Chemistry

Zincke's aldehyde (61) and cyanomethyltriphenylphosphonium chloride in acetic anhydride at 100 "Cgave 38 the salt (62), isolated as the perchlorate, whereas the same reagents in pyridine gave the phosphorane-phosphonium salt (63), presumably via nucleophilic addition of cyanomethylenephosphorane to the terminal carbon of (62). PhNMeOCH: CH*CH:CH-CHO

+

Ph,Pi *CH,CN CI-

(61)

PhN Me*CH:CH : CH :CH*CH:C(CN)*P+Ph, (62) 1' y r i (1 i ti (!

1

1 L.T.

Ph,P: C(CN)-CH:CH*CH: CH-CH :C(CN)*P Ph, I (63)

The allylidenephosphorane (64) with phenanthraquinone gave 39 the pyran (65) together with small amounts of (66) and (67). Similar pyrans were also obtained from (64) and a-naphthoquinone and tetrachloro-obenzoquinone. Among other olefins prepared in conventional ylide reactions with carbonyls are (68),40(69),41(70),42and (71).43 38

Bp O0 41 42 43

A. V. Kazymov and E. B. Sumskaya, Zhur. org. Khirn., 1970, 6, 1944 (Chern. A h . , 1970, 73, 109 842). G. Cardillo, L. Merlini, and S. Servi, Ann. Chim. (Italy), 1970, 60, 564. B. Miller and K.-H. Lai, Tetrahedron Letters, 1971, 1617. J. Meinwald and D. A. Seeley, Tetrahedron Letters, 1970, 3739. J . Meinwald and D. A. Seeley, Tetrahedron Letters, 1970, 3743. M. I . Shevchuk, A. S. Antonyuk, and A. V. Dombrovskii, Zhrrr. org. Khitn., 1970, 6, 2579 (Chew. A h . , 1971,74, 64276).

YIides and Related Compounds

I61

g. I

/

CH,.CH,OH CH:C Me,

CH: C Me,

Ph:,t’: (‘Me,

CH:CMe,

P$P:CX*COR

+ ArCHO

PhMe

ArCH:CX-COR (71)

X = H, C1, Br, or I R = a-benzofuranyl or 3-dibenzofuranyl

162


The formation of the naphthalene (73) from the bis-ylide (72) and diethyl ketomalonate 4 4 involves an unusual olefin synthesis on the carbonyl of an ester group. The methylene-pyrans (75) were formed46 when the diethyl malonates (74) were refluxed with /I-keto-ylides in xylene or decalin. Possible intermediates are the ketens (76) and the allenes (77). Addition of ylide to the allenes gives the betaines (78) which form methylene-pyrans either directly or via acetylenes as shown.

a

C H :P Ph,

+ (EtO,C),CO

CH :PPh,, (72)

2 Ph,P:CIi.C'OK'

-

m I E ;t (73)

+ R'CH(C0,Et)2

-+ 2 Ph3P0

R? = I1 o r M e

(55)

+ R1 (75)

(74)

/R'

Et02C liC=C, \ / 0C=C K'

I Et0,C

\

HC=C /

.

A

I-

pt':'''O

R' /

E l 01.c

\

\

HC=C,

c=c/

/

R' OH

(75) 44 45

W. H. Ploder and D. F. Tavares, Cunad. J . Chem., 1970, 48, 2446. H. Strzelecka, M. Dupre, and M. Simalty, Tetrahedron Letters, 1971, 617.

163

Ylides and Related Corripouiids

(iii) Miscellaneous. Symmetrical olefins were obtained Q6 from reactive ylides and sulphur under fairly vigorous conditions. Yields were high when R = Ar, but the ethylidenephosphorane gave only 28% of hex-3-ene at 150 “C in 1 -methylnaphthalene. Ph,P:CHR

+ S8

RCH:CHR

+ Ph,PS

The triazoles previously obtained from 6-keto-ylides and acyl azides or ethyl azidoformate are 47 the 2-acyltriazoles (80) formed by isomerization under the basic conditions of the initially formed 1-substituted triazoles (79). The latter can be isolated in some cases if the reactions are interrupted. Aryl mono- and bis-azides have also been used 4 s in the preparation of the triazoles (81).

I

H

R1

R2

N%N-Ar

The reaction between benzylidenetriphenylphosphorane and benzonitrile has been reinvestigated and the primary product (82) isolated. Stable ylides react similarly with activated nitriles, e.g. cyanogen and trifluoroacetonitrile, but cyanomethylenetriphenylphosphorane with methyl cyanoformate gave largely the vinyl ether (83), the product of a normal olefin synthesis on the carbonyl of the ester group. Diphenylcarbodi-imide reacts with ylides 50 to give, in general, the iminophosphorane (86) and the imines (85). The latter usually react with a second mole of ylide to give the stable phosphoranes (87) although the imine (85; R1 = R2 = Ph) was isolated. Hydrolysis of the solution M 41

O@

H. Mtigerlein and G . Meyer, Chem. Ber., 1970, 103, 2995. P. Ykman, G. L’AbbC, and G. Smets, Tetrahedron Letters, 1970, 5225. P. Ykman, G. L’AbbC, and G . Smets, Tetrahedron, 1971, 27, 845. E. Ciganek, J . Org. Chem., 1970, 35, 3631. Y. Ohshiro, Y . Mori, T. Minami, and T. Agawa, J . Org. Chew?., 1970, 35, 2076.

164


resulting from treatment of the carbodi-imide with methylenetriphenylphosphorane in DMSO gave the amidine (88), presumably formed via proton transfer in the intermediate (84; R1 = R2 = H).

J

Ph,P:N-C(CN):CH.CN 2 isomers

(c”Y Ph,P:CH.CN (h Me(),(-.

Ph,PO

+ NC.CH:C(OMe).CN (83) -t

Ph,P:C R’K’ + PhN:C :NPh +Ph3P-C R’R2 PhN-&:NPh (84)

R* = R? =

[Ph,P:CH.C ( N HPh) :NPh]

I

/ I

Ph,P:NPh

H,O

Me(NHPh):NPh

+ Ph,PO

(86)

+ R’R2C:C:NPh (85)

I PIi,P:CR’-C (CH,R’):NPh

(87)

Ethylidenetriphenylphosphorane and N-methyl-N-phenylthioacetamide (89) in THF gaveK1a suspension from which the vinyl thio-ethers (91) were obtained on treatment with carbonyl compounds. The suspension O1

T. Mukaiyama, T. Kumamoto, S. Fukuyama, and T. Taguchi, Bull. Chem. SOC.Japan, 1970,43, 2870.


165

was probably the salt (90) in equilibrium with the phenylthio-ylide. Methylenetriphenylphosphorane with the same reagent (89) gave the bis(pheny1thio)-ylide (92). Ph,P:CH Me

+ PhS-NMe-COMe -+Ph,&CHMe-SPh (89)

(90)

+ (89) --+

Ph,P:CH,

MeN-COMe

Ph,P:C(SPh), (92)

Vinylsulphonium salts and ylides gave 6 2 cyclopropylphosphonium salts (95) via proton transfer in the initial adducts (94). C-Methylation of the

ylides also occurred with dimethylvinylsulphonium salts, whereas the ylides (93; R1 = H, COPh, or p-NO,*CBHI) gave only the corresponding phosphonium salts.

+

Ph,P.CHMeR' X+

Ph,P:CHR' (93)

u2*

u'

=

+ K2CH:CH.SR3R4 X-

R'

\

= 14.

+

+ R2CH:CH.SMe

COPh. p-NO,.C,HI

i-

+ Ph3P.CH,R1 X-

Ph3P*CHR1 R2&H.CH. i R 3R4 (94)

I

A normal olefin synthesis took place53 between a carbonyl ligand of bromopentacarbonylmanganese and hexaphenylcarbodiphosphorane to give an organometallic ylide. ba

bs

R. Manske and J. Gosselck, Tetrahedron Letters, 1971, 2097. D. K. Mitchell, W. D. Korte, and W. C. Kaska, Chem. Comm., 1970, 1384.

I66

Organophosphorirs Chemistry Ph,P:C:PPh,

+

MnBr(CO),

('sllo, Mn(CO),Br(:C:C: PPh,) 4 0 "C'

Semi-empirical molecular orbital calculations have been carried out 64 on the model phosphorane H3P:CH2. Besides the expected transfer of charge, the inclusion of the phosphorus 3d orbitals showed a significant hyperconjugative interaction between the CH2 orbitals and a 3d orbital of appropriate symmetry on phosphorus. Calculations on cyclopropylidenephosphorane revealed 65 a similar interaction between the Walsh orbitals of the ring and an in-plane phosphorus 3d orbital. For the n.m.r. spectra of /3-keto-ylides see Chapter 1 I , and for their photolysis see Chapter 10.

2 Phosphoranes of Special Interest A kinetic investigation 66 of the reaction between cyclopentadienylidenetriphenylphosphorane (96) and tricyanovinylbenzene to give the phosphorane (97) has identified the slow step as nucleophilic attack of the phosphorane on the olefin. This is then followed by a rapid intramolecular proton transfer. An Elcb mechanism has been postulated 67 for the basecatalysed elimination of hydrogen cyanide from (97), rapid proton loss giving an ion-pair from which cyanide ion is lost in the rate-determining step. The reactions between the phosphorane (96) and a series of benzylidenemalononitriles have also been carefully investigated 6H and a mechanism proposed involving n-complex formation between the phosphorane and the cyano-olefins. Semi-empirical molecular orbital calculations on the phosphorane (96) p h l P/ O

(96)

6K 66

67

6R

+ PhC(CN):C(CN),

'Q

d Ph,P

PhC (CN )

- c (CN

12

R. Hoffman, D. B. Boyd, and S. Z. Goldberg, J. Amer. Chem. SOC., 1970, 92, 3929. D. B. Boyd and R. Hoffman, J. Amer. Chem. SOC.,1971, 93, 1064. E. Lord, M. P. Naan, and C. D. Hall, J. Chem. SOC.(B), 1970, 1401. E. Lord, M. P. Naan, and C. D. Hall,J. Chem. SOC.(B), 1971, 220. E. Lord, M. P. Naan, and C. D. Hall, J. Chem. SOC.( B ) , 1971, 213. Z. Yoshida, K. Iwata, and S. Yoneda, Tetrahedron Letters, 1971, 1519.

YIides and Related Compounds

I67

and its U.V.spectrum show that in the ground state it has 88% of P+-C character and 12% of P: C character. This is not due to aromatic stabilizaion of the cyclopentadiene anion, as calculations on the rnethylene ylide give a similar result. The phosphorane (96) readily undergoes electrophilic substitution at the 2-position and adds to electrophilic olefins also at this position.s1 Thus, nitration with ethyl nitrate and aluminium chloride or with nitronium borofluoride gave the 2-nitrophosphorane (98), Vilsmeier formylation gave the 2-aldehyde (99), and diethyl acetylene dicarboxylate gave the phosphorane (100). No Diels-Alder adduct was obtained from (96).

Ally1 vinyl ethers have been prepareds2 using the ylide (101) but only from non-enolizable carbonyl compounds. The ethers rearrange on heating to give a-ally1 aldehydes, e.g. (102).

I

Ph

N,P,F,*N=PX3 -(Me# i )2NH ~

N3P3F,.N=PX2N=PC12.N=PCI,

N,P,F,. N=PX,NHSi Me:,

(X = F or CI)

Scheme 3

(Me,Si),NMe, not only took place at the trichlorophosphazenyl groups e.g. N,P,F, -N=PCI,

-

+ (Me,Si),NMe N,P,F,.N=PCI,*NMeSiMe,

+ Me3SiCI

but also at the phosphazene ring fluorine atoms. Methylamine, a n even stronger nucleophile, was able to displace two of the chlorine atoms in the N=PCI(NH Me),. The trichlorophosphazenyl group to give, e.g., N3P3Fb* related derivatives, N,P,F2n-1R (n = 5 ; R = NH2 or N=PCl,), were also reported. Dimethylaminolysis B3 of the novel fused ring compound (42), whose crystal structure has just been reported (see Section 7), gave a derivative of probable structure (43) on the basis of lH and 31P n.m.r. data. On the Mc,N

NMe,

/ /

NMc,

CI

N Me2

c1 Me,N (42) DS

/\

NMe,

(43)

W. Harrison, R. T. Oakley, N. L. Paddock, and J. Trotter, Chcm. Comm., 1971, 357.

Phosphazenes

217

other hand, attempted fluorination and methoxylation of (42) resulted i n the breakdown of the ring system. The donor properties of N3P3C16appear to be too weak to allow complex formation with metal halides, but it has been reported B4 that complex formation between N,P,CI, -NHBu" and Cu" or Co" chlorides in acetonitrile solutions can be detected by U.V. spectroscopy. Attempts to isolate the complexes were unsuccessful. The previously-reported alkylation reactiys of aminocyclophosphazenes by trimethyloxonium fluoroborate, Me,0BF4-, have been e ~ t e n d e d . * ~ With the dimethylamino-derivatives, N3P3Cl,-,(NMe,), (n = 1--4, or 6), a series of monomethylated derivatives, e.g. (44), was obtained, in which

/ \

CI

c1

'H n.m.r. spectroscopy showed that methylation took place on an exocyclic nitrogen atom. The salt-like nature of these products was confirmed by conductivity measurements. In contrast, the isopropylamino-derivatives, N3P3CI2( NH Pr9, and N,P3( N Me2)z(N H PI-*)^, were preferentially met hylated on the ring nitrogen atoms (the latter was also methylated at an NMe, group). The formation of (45) is interesting, since protonation of

the same base was shown by X-ray crystallography to take place at the identical ring nitrogen atom. N3P,Ph6 was, as expected, methylated at a ring nitrogen atom to give [N,P,Ph,Me]+ BF,-. Reactions of N,P,Cl, with aniline in benzene were showns6 to take the predominantly geniinal chlorine atom replacement route shown in Scheme 4. The structures were established by basicity measurements, and by the 84

R. W . Jenkins and S. Lanoux, J . Inorg. Nuclear Chem., 1970, 32, 2429. J. N. Rapko and G . Feistel, Inorg. Chern., 1970, 9, 1401. V. B. Desai, R. A. Shaw, and B. C. Smith, J . Chenr. Suc. ( A ) , 1970, 2023.

21 8

Orgcrnopliosphoriis Chemistry

(

= phosphorus atom; spokcs on rings represent incoming anilino-groups)

Scheme 4

preparation of the mixed amino-derivatives, N3P3(NMe,)6-,(NHPh),h (n = 1-5), whose lH n.m.r. spectra were examined in detail. These derivatives were obtainedfrom eitherchloroanilino- or chlorodimethylaminoderivatives, the latter being of known structure. The use of n-butylamino-derivatives of cyclophosphazenes in flameproofing cellulose-based fabrics has been described in a patent applicat i ~ n . ~The ' topic of flame retardants is also covered in a recent review,*8 where phosphazenes are important because of their relatively high phosphorus and nitrogen contents. B. Alkoxy- and Aryloxy-derivatives.-The preparation and physical properties of a series of thermally stable monoalkoxy (or aryloxy) fluorocyclophosphazenes have been reported :e9 N,P,F,

+ NaOR

Et2O

>

N,P,F,OR

+ NaF

(R = Me, Et, or Ph) Thiolysis by NaSR under the same conditions gave 9D N3P3F,SR (R = Me or Ph). Ligand-exchange reactions between a series of organo-substituted cyclotriphosphazatrienes have been studied loo and their synthetic potential demonstrated. Typical of these reactions is : Nap3(0C6H, -p-NOz)a

+ 6Na OCH,C F, N,P,(OCH,CFJ,

+ 6NaOC,H4-p-N02

(70% yield)

loo

P. Braune, H. Pohlemann, J . Swoboda, and R . Wurmb, G . P. 1 904 427 (Chenr. A h . , 1970,73, 89 052w). S. J. O'Brien, Textile Chemist and Colourisf, 1970, 2, 201. E. Niecke, H. Thamm, and 0. Glemser, Z . Nururforsch., 1971, 26h, 366. H. R. Allcock, R. L. Kugel, and E. J. Walsh, Chem. Comm., 1970, 1283.

Phosphazenes

219

An order of reactivity for a series of nucleophiles towards a given substrate could be drawn up and, in general, this follows the order: amines < alkoxides, aryloxides c organometallic reagents The latter group, including reagents such as methyl magnesium iodide and phenyl-lithium, had a considerable disadvantage in that cleavage of the phosphazene ring often occurred. Reactivity to nucfeophiles was generally increased when a five-membered ring was present at the phosphorus atom (in the phosphazene ring) so that, for example, the P-0 bond in

may be cleaved by weaker nucleophiles than in

The lability of certain alkoxy-groups has also been shown101 in the reactions:

Similar reactions with heptafluorobutoxy-derivatives have also been demonstrated. In order to obtain compounds with Ti-0-P and Zr-0-P units, the hexaethoxy-derivative, N3P3(OEt)6, was treated lo2 with titanium and zirconium tetrachlorides. I n each case, hygroscopic solids of the type N,P3(0Et),02MC12 (M = Ti or Zr) and ethyl chloride were obtained. The degree of polymerization of these solids was 1.6-1.8, and on the basis of their i.r. and 'H 1i.m.r. spectra, two alternative structures, (46) and (47), were proposed. In an alternative route to the same type of compound, N,P,Cl, was treated lo3 with tetra-n-butoxytitanium in o-xylene. Butyl chloride was liberated and a solid was obtained which has been assigned the structure (48). Its thermal decomposition was studied by differential thermal analysis. The synthesis and properties of cyclodiphosphazatrienes of type (49) and (50) are well documented. A series of P-alkoxy- and -aryloxy-derivatives V. N. Prons, M. P. Grinblat, A. L. Klebanskii, and G . A. Nikolaev, Zhur. obshchei Khim., 1970,40, 2128 [J. Gen. Chem. (U.S.S.R.L 1970, 40,21091. l o o Yu. A. Buslaev, B. V. Levin, Z. G . Rumyantseva, S. P. Petrosyants, and V, V. Mironova, Russ. J . Inorg. Chem., 1969, 14, 1711. lUs Yu. A. Buslaev, B. V. Levin, Z . G. Rumyantseva, and V. V. Mironova, Russ. J . Iitorg. Chenr., 1970,:15, 1690.

220


OBu“ I .Ti

I

0Ru“

K

R

( 50)

(51)

of (49) and (50) has been obtained (49)

+ 4R10H + 4C5H5N (R = Ph;

lo4

by two routes. The first route:

----+

(51)

+ 4C5H,6H 61

R L = Pr” or Bu”)

was not generally satisfactory, since proton transfer from the pyridine hydrochloride to the more basic derivatives, e.g. (51 ; R = Me, R 1 = Bu”) resulted in cleavage of the ring system: (51)

H +-I?

U”OII+

--___

+

(Bu”O),P=N. P(O)(OBU~ )~ [H,N=C(Me)NH,]+ C1-

The second route:

was generally more satisfactory and was used to obtain the following derivatives : R = Me

Me

Me

R1 = Me Bun p-MeC,H,

Ph

Ph

Ph

Me

Et

p-MeC,H,

Me Et NMe2

In many cases, trialkoxy-derivatives of (49) were obtained using suitable quantities of sodium alkoxides. The 31Pn.m.r. spectra of this latter group of compounds were simpler than the tetrakisalkoxy-derivatives, enabling lflJ

A. Schmidpeter and N. Schindler, Z . ariorg. Cherti., 1970, 372, 214.

22 1

Phosphazenes

the P-N-P spin-spin coupling constants (50-64 Hz) to be obtained, which were typical of those values obtained in cyclotriphosphazatrienes. Alkoxy- and aryloxy-derivatives of (50) were obtained by both routes as mixtures of cis- and trans-isomers. It was found lo5 that N,P,CI, was progressively dehydrochlorinated by reactions with increasing molar proportions of hydroquinone. Reactions in acetone, DMF, and dioxan gave a series of decomposition products, but the addition of HOC,H,ONa to the solution enabled crystalline products, N3P3(O2C,H5),(mol. wt. 760) and N,P,(O,C,H,), (mol. wt. 940) to be isolated. The use of N,P,CI, in the synthesis of amides has been described,Ios although the fate of the phosphazene ring system was not clear: R'NIT2

R = alkyl or aryl

>

RCO-NHR'

+ 'decomposition products'

1

R1 = Et or cyciohexyl

The addition of aldehydes to N,P,CI, in the presence of pyridine has also been studied.lo7 Mention has already been made of the application of alkoxycyclophosphazenes, [NP(OR),],, as flame retardants in rayon.' Although the methoxy-derivatives, with their high phosphorus content, were expected to be most efficient in this respect, their water solubility proved a major shortcoming. However, the n-propoxy series, [NP(OPrn),],, (n' mainly 3--6), were found to impart excellent flame resistance and were well retained by rayon. The cyclophosphazene alkoxides were obtained by the addition of sodium-n-propoxide to the chloride homologues, (NPCI2),, and were added to the viscose dope before the rayon was spun. The flame resistance imparted by various amino- and thioalkoxy-derivatives was also tested, but found to be inferior to the results obtained with alkoxy-derivatives. Several patent applications have resulted from work on this topiC~lO"ll~

C. Alkyl and Aryl Derivatives.-Reactions of organometallic reagents, such as methyl-lithium, with fluorocyclophosphazenes are, in general, In5 loo

10) lo8 log

lln 111

M. Kajiwara and H . Saito, Kogyo Kagaki4 Zasshi, 1970, 73, 1947 (Chem. Abs., 1971, 74, 88 340x). G. Baccolini and G . Rosini, Chim. Ind. (Milan), 1970, 52, 583. V. K. Taksidi and B. I. Stepanov, Zhur. org. Khim., 1970, 6, 815. L. E. A. Godfrey, G . P. 2016 153 (Chem. Abs., 1971, 74, 3 2 6 2 0 ~ ) . H. Pohlemann, R. Wurmb, and P. Braun, G . P. 1906 381 (Chem. Abs., 1970, 73, 99 962g). Badische Anilin- and Soda-Fabrik A.-G., Fr. P. 2 012440 (Chem. Abs., 1970, 73, 121 501e). R. Wurmb, J. Swoboda, H. Pohlemann, and M . Jacobi, G . P. 1926 169 (Chem. Abs., 1971,74, 43 489m). R. C. Harrington, U.S.P. 3 530 204 (Chem. Abs., 1970, 73, 99 963h).

222

0rgnrr ophosph o rus Che m is t r y

cleaner than with chlorocyclophosphazenes, because ring-cleavage reactions are minimized. This feature has enabled the following derivatives to be obtained looin reasonable yields: N3P3F6

+ RLi

-

N,P3F,R

+ LiF

(R = M e o r CH=CH,)

The stepwise replacement of fluorine atoms in fluorocyclophosphazenes, (NPF,),(n = 3-9, by methyl groups has been followed.113 lH and lVF n.m,r. spectroscopy showed that methyl-lithium in diethyl ether generally effects a geminal replacement pattern. With N3P3F6, only mono- and di-methyl derivatives were obtained, but with N4P4FBthe dimethyl (52), trimethyl (53), and octamethyl derivatives were noted. The formation of Mc

Me

/ \

F

1-‘

Me

Me

/I

F Me

(53)

compounds of structure (52) and (53) is unexpected on simple electrostatic grounds, since reactions with nucleophilic species would be expected at fluorinated rather than at methylated phosphorus atoms. I t has been suggested that the formation of these two structures may be understood in terms of substitution at the phosphorus atoms with the least n-induced negative charge, Huckel-type molecular orbital calculations show that increasing r-induced negative charge on the phosphorus atoms in (52) follows the order: P-1 < P-3 < P-2, i.e. so that P-2 is least attractive to nucleophiles, as found. A decamethyl derivative, N5P5Me10, was also reported.

The first example of an optically active cyclophosphazene (54) has been obtained 114 by elegant experimental work. The route chosen is summarized in Scheme 5.

114

N. L. Paddock, T. N. Ranganthan, and J. M. Todd, Cunad. J . Chetn., 1971, 49, 164. C. D. Schmulbach, C. Derderian, 0. Zeck, and S. Sahuri, Inorg. Chenr., 1971, 10, 195.

223

Phosphazenes

Scheme 5 A detailed description of the experimental aspects of the preparation of the fluorophenylcyclotriphosphazatrienes(56) and (57) has been given.ll’

(55)

I’Ill,i

I’IIII- 4lC‘la

( 5 6 ) ---A (57)

The near-u.v. absorption spectra of a series of halogenophenylcyclotriphosphazatrienes, N3P3X6-,Ph, [X = F, n = 2 (3 isomers), n = 4 (geminal isomer); X = F, n = 5 ; X = Cl, n = 2 (geminal isomer), n = 4 (geminal isomer); n = 61 have been compared 116 and suggest that weak conjugation takes place between the phenyl groups and the phosphorus atoms. A new borohydride derivative of a cyclophosphazene has been obtained

116 ‘17

C. W. Allen and T. Moeller, Inorg. Synth. 1970, 12, 293. A. J. Wagner and T. Moeller, J . Inorg. Nuclear Chetn., 1971, 33, 1307. N. T. Kuznetsov and G . S. Klimchuk, Russ. J . Inorg. Chern., 1970, 15, 1496.

224


D. Pseudohalogeno-derivatives.-Little work has been carried o u t in this area. Isocyanates of cyclic phosphazenes, previously unknown, are thought lr8 to be formed in the reaction of N,P,Br, with AgOCN in nitromethane. They were detected by i.r. spectroscopy, and underwent ready polymerization, which precluded their isolation. On the other hand, isothiocyanates, [NP(NCS),], (n = 3 or 4), are well known and a detailed study of their spectra has been reported.llQ The azide, N3P3(N3),,has been the subject of an i.r. study which suggests120that the molecule has D3,, symmetry. 6 Polymeric Phosphazenes

Linear phosphazene polymers, obtained from the reaction of ammonium chloride with phosphorus pentachloride in chlorobenzene, may be rendered hydrolytically stable by reaction 131 of one of the terminal chlorine atoms with, for example, sodium phenoxide: C1[N=PCI2].PCI4

+ NaOPh

(mol. wt. -800)

-

CI[N=PCI,],PCI,OPh

+ NaCI

Dimethylamine, aniline, phenol, and ethanol have also been used with similar effect. The monophosphazenes, CI,P=N. P(OjCI,, and Ph,PCl= N P(O)CI,, give polymers of the type CI[CI,P=N],,* [PCI=N],,; P(O)CI,

(X = Ph, Y = CI)

I

N=PX,Y

when heated together.*22 When Et,P=N P(O)CI, was used, a similar polymer (X = Y = Et) was obtained. The thermal decomposition of (NPCI,), (linear polymer) follows first-order kinetics and has an activation energy of 22.5 kcal mol-l. Decomposition is thought to be initiated at the ends of the macro-chain and gives products which include a wide range of cyclic and linear phosphazenes. The properties of fluoroalkoxyphosphazene polymers and copolymers [N=P(OR),], (R = fluoroalkoxy-group) have been described.124 Condensation of the phosphazenes, (CI,PNPhj, and C,N,(N= PCI,),, with 6

lln 118

IZ0

lz3 lZ4

E. Steger and G . Bachmann, Z . Chem., 1970, 8, 306. A. J. Wagner and T. Moeller, J . Chem. SOC.( A ) , 1971, 596. F. Rauchie and M. Gayoso, Ann. Fis., 1970, 66, 241 (Chem. Ahs., 1971, 74, 58 865e). R. G. Rice, R. M . Murch, and D. C. De Vore, U.S.P. 3 545 942 (Chetn. Abs., 1971, 74, 54 398g). A. Ya. Yakubovich, I. M. Filatova. E. L. Zaitseva, and V. S. Yakubovicli, Vysokond. Soedineriii Ser. A , 1970, 12, 585 (Chmi. Ahs., 1970, 73. 458 935s). J . R. MacCulluni and A. R . S. Wernick, J . Mncmriiol. Sci. Clierri., 1971, 5,6 5 I (C'/wtii. Abs., 1971, 75, 64 569c). S. H . Rose, K . A. Reynard, and J. R . Cable, US. Clearinghouse Fed. Sci. Tech. Inform., A D 1970, No. 704 332 (Chetn. Abs., 1970, 73, 99 778b).

Phosphazenes

225

urea or with melamine gave a new series of polymers whose thermal stability has been examined.lZ6 The reactions of chlorosilanes with alkoxyphosphazenes have already been mentioned (Section 3). This type of reaction has been exploited 126 to obtain polymers containing

I

I

I

I Me

-N=P-O-CH2-Si-O-

units from alkoxycyclophosphazenes, N3P3(OR)6,and oligomeric chloromethylsiloxanes. Other polymers have been reported from the reactions of N3P3C16with alkoxyboron the sodium salt of hydroquinone,128 and 4,4'-dihydroxybiphenyl . l Z 9 n6 S. M. Zhivukhin, V. V. Kireev, S. S. Titov, and G. S. Kolesnikov, Trudy Mosk. Khim.-Techknol. Inst., 1969, 200 (Chem. Abs., 1970, 73, 15 3542).

127 la8

128

V. V. Kireev, I. M . Raigorodskii, and G. S. Kolesnikov, Plust. Massy., 1970, 26 (Chenr. Abs., 1971, 74, 32 246d). A. V. Deryabin, S. M. Zhivukhin, V. V. Kireev, and G. S. Kolesnikov, Trudy Mosk. Khinr.-Teckhnol. Inst., 1969, 206 (Chem. Abs., 1970, 73, 15 630m). T. Okuhashi and Y. Watanabe, Kogyo Kugaku Zasshi, 1970, 73, 1164 (Chem. Abs., 1970, 73, 1 I0 187f). M. Kajiwara and H . Saito, Kogyo Kagaku Zasshi, 1970, 73, 1954 (Chenr. Abs., 1971, 74, 76916b).

1.567 (6)

P-N

(A)*

P

,NCS

D

,CI

13'

133

13*

131

130

1.581 (5)

1.575 (7)

P-c

P-N 1.63 119

121

102.1 ( I )

1 1 8.5 (5)

2.162 (4)

P-Br

121.4 (3)

142 (1)

1 1 8.4 (2)

d

XNX

/\

124.2 (5)

("I*

1.993 (2)

P-CI

1.79

-

I

NPN

I\

Comments

plane. PNC = 152"

/\

Ring planar except for one N atom which is 0.15 8, out of

ficantly different PNP angles (119.3 and 122.4")

/'A

Improved structure determination. Slight chair conformation, signi-

Improved structure determination. Greatest difference from previous results is in P-CI bond lengths (before 1.97 A)

Four of the phenyl groups bonded to P-N-P unit have conformations similar to the phenyl groups in N3P3C12Ph4

P-N shorter than in Ph,FP=NMe (1.641 A). N-Aryl group 35" out of P-N-C plane

Diffraction Methods

Average bond annles -

M. J. E. Hewlins, J . Chem. Soc. (B), 1971, 942. L. B. Handy, J. K. Ruff, and L. F. Dahl, J. Amer. Chem. SOC.,1970, 92,7312. L. B. Handy, J. K. Ruff, and L. F. Dahl, J. Amer. Chem. Soc., 1970, 92,7327. G. J. Bullen, J. Chem. SOC.( A ) , 1971, 1450. H. Zoer and A. J. Wagner, Acra Cryst., 1970, B26, 1812. J. B. Faught, T. Moeller, and I. C. Paul, Inorg. Chem., 1970, 9, 1656.

*Standard deviations in parentheses.

SCN\

Cl,

[Ph3PIIINEPPh3]+[Cr2(CO),,l]-

1.80

P-c

1.809 (8)

P-x P-c

Average bond distances

[Ph3PIIINfflPPh3]2+[M2(CO),,]2-CH,CI, 1.570 (15) (M = Cr or Mo)

Compound

7 Molecular Structures of Pbosphazenes Determined by &Ray

135

I34

133

132

131

130

Ref.

P

,OPh 117.3 (3)

118.5

P-0 1.584

NPN

1.582 (2)

P-0

P-x

P-F 1.52 (1) P-C 1.81 (1)

P-8N-1 1.59 (1) P-2N-1 1.53 (1)

N- 1P-2N-3 125.9 (9)

XNX

134.6 (7)

121.0

121.9 (3)

6

NP-8N-1 117.5 ( 5 )

As preliminary report (Vol. 1 )

1.575 (2)

P-N

/\

("I*

(A)* /\

Acerage bond angles

Arerage bond distances

Me 'Me *Standard deviations in parentheses. la6 W. C. Marsh and J. Trotter, J. Chew?.Soc. ( A ) , 1971, 169. l S i H. R. Allcock, M. T. Stein, and J. A. Stanko, Chem. Comm., 1970, 944. 138 N. V. Mani and F. H. Ahmed, Acta Crysf., 1971, B27, 51. l J 0 W. C. Marsh, T.N. Ranganthan, J. Trotter, and N. L. Paddock, Chem. Comni., 1970, 815. I4O W. C. Marsh and J. Trotter, J. Chern. SOC.( A ) , 1971, 573. 141 W. C. Marsh and J. Trotter, J.Chern. Soc. (A), 1971, 569.

Me, ,Me

N,P,CI,( NHPr'),HCI

PhO,

Compound

Ring has 'saddle' conformation. Variation in P-N bond lengths consistent with n-bonding theory

Three independent P-N bond lengths. OPO = 102.7"' exocyclic groups twisted at 48" to average plane of phosphazene ring

P-0-C = 123", ring slightly nonplanar with two N atoms 0.15 8, out of plane of other four atoms

Comnients

139, 141

138

137

136

Ref.

5

3

Z,

$

b

3-

N

CI

\

F

14'

143

14*

P-x

1.601.65 (2) (N-CU bonded) 1.531.57 (2)

i

P-N 1.621.68 (2)

P-F P-8N-1 1.4811.584 P-2N-1 1.495 (8) 1.470 (6) P-c P-2N-3 1.794 (8) 1.532 P-4N-3 1.487

P-N

(A)*

Acerage bond distances (O)*

XNX

/\

97.2115.4

119.G 122.4

Others 124.6, 126.1

NP-8N-1 116.9 ( 5 )

132.4137.6

133.2141.8

Other 143.3 (6)

P-8N-1P-2 146.7 ( 5 )

nA

NPN

/\

Average bond angles

G. J. Bullen and P. A. Tucker, Chem. Comm., 1970, 1185. W. C. Marsh, N. L. Paddock, C. J. Stewart, and J. Trotter, Chem. Conrm., 1970, 1190. W. C. Marsh and J. Trotter, J . Chem. SOC.( A ) , 1971, 1482.


[N,P,( N Me,) ,,CuCI]-CuCI,-

/L

Ph

C1

Ph

F

/ P\

\a/

3

/F

'2P\ /

IN\

F

F \ /N P / \ F N

/ 8 \

P

Me\ / Me

Compound

5-co-ordinated Cu on C, axis. NMe, groups nearly planar

Flattened crown conformation

Contains shortest known P-N bond (1.470 A). Alternation of P-N bond lengths may be explained in terms of .rr-bonding

Comments

143, 144

142

139, 140

Ref.

-4

.=.

2

3

2

s

h

2 g

0

00 w

t3

c ,1

I

x

Ph

II Ph

P' \

14'

146

PN-P 1.597 (2) CN-P 1.608 (2)

PN-P 1.567 (3) CN-P 1 A20 (3)

P- 1N-2 1.571 P-3N-2 1.558 P-3N-4 1,723

P-N P-x

-

P-c 1.802 (2)

P-c 1.801 (2)

P-3-Cl 2.004

P-1-CI 1.979

(A>*

Average bond distances (O)*

XNX

/\

Comments

115.4 (2)

-

-

117.1 (lo) 115.4 (10)

116.5 (2)

F

/ \

F

One form has cis-frans orientation in repeating unit, i.e. F F, / /P=N, N P=

Skew boat conformation. NMe, group planar and in plane of phosphazene ring

Slightly non-planar, in skew boat conformation

P-IN-2P-3 Central NP, almost planar, but other N and P atoms puckered 125.5 A out of this plane N-2P-3N-4 104.0

NP-1N-2 116.9

NPN

/\

Average bond angles

D. R. Pollard and F. H. Ahmed, Acta Crysf., 1971, B27, 163. D.R. Pollard and F. H. Ahmed, Acta Crysr., 1971, B27, 172. H.R. Allcock, G . F. Konopskii, R. L. Kugel, and E. G . Stroh, Chem. Comm., 1970, 985.


N

/

N//C'N

Ph\l yh/P+

Ph

II /Ph /p\ N Ph NMe,

2,

Pl1,I

N//C"

I

Me

CI

P N/l>N C1,II 3 iC ,1 2% /p+. " N C1i, I

CI,

Compound

147

146

145

93

Re; b

:

tu

$-

0

s

I0 Rad ical, Photochemical, and Deoxygenation Reactions BY R. S . DAVIDSON

1 Radical and Photochemical Reactions The formation of diphenylphosphino radicals on photolysis of triphenylphosphine,'. diphenylphosphine,l and tetraphenylbiphosphine 1 r has been verified. In the case of the reactions of the phosphines, the radicals were trapped with t-nitrosobutane and the resultant nitroxyl radical [Ph2PN(b)But]was identified by e.s.r. The nitroxyl radical has a small 31P splitting constant, demonstrating that there is no extensive delocalization onto the phosphorus atom. The e.s.r. spectrum of diphenylphosphino radicals, generated by photolysis of tetraphenylbiphosphine in benzene at 77 K, has been o b ~ e r v e d .When ~ methanolic solutions of the biphosphine or triphenylphosphine are flash-photolysed, a transient species having A,,,,, = 330 nm and which decays by first-order kinetics (k 4 x 10 -3 s-l) is observed. The absorption spectrum was assigned to the diphenylphosphino radical. The validity of the previous claim that diphenylphosphino radicals abstract hydrogen from the 0 - H bond of alcohols has been questioned, Irradiation of the biphosphine in deuteriated methanol (MeOD) was found to produce unlabelled methanol. Reaction by abstraction of hydrogen from the a-C-H bond of the alcohol was postulated as N

ill.

Ph2P-PPh, -+ Pt1,P.

+ CH,OL) + Ph,PII + .CH,OI> Ph,Pli + CH3013 --+ Ph,PD + CFl,OIi

Ph,P-

shown. However, products derived from the hydromethyl radical (.CH,OH) have not been detected. In the case of the reaction of the radicals (produced from triphenylphosphine) with propan-2-01, it was conclusively shown that acetone was not produced. Formation of this compound would be expected if abstraction from the a-C-H bond had occurred, Clarification of this situation is awaited with interest. a

H. Karlsson and C. Lagercrantz, Acta Chem. Scand., 1970, 24, 3411. S. K. Wong, W. Sytnyk, and J. K. S . Wan, Canud. J. Chem., 1971, 49, 994. S. K. Wong and J. K. S. Wan, Spectroscopy Letters, 1970, 3, 135. R. S. Davidson, R. Sheldon, and S. Trippett, J . Chem. SOC.( C ) , 1966, 722; Chem. Comm., 1966, 99.

Radical, Photochemicd, and Deoxygetiririon Recrcfioiis

23 1

The formation of the biphosphines ( 1 ) and (2) by reaction of tetramethylbiphosphine with buta-l,3-diene has been rationalized in terms of participation of dimethylphosphino radicals as intermediates.5 Reaction

(2)

(1)

by the concerted addition of the biphosphine to the cis-diene could be ruled out since only (1) should have been formed by this route. It was shown that (1) and (2) are not equilibrated under the reaction conditions. The reaction with isocyanides of phosphino radicals, generated by the reaction of secondary phosphine with AIBN, gives the nitrile (4) as well as the expected product (3).6

Et,P*

+ RNC

t t-l’t I

---+

EtLPC=NR -+

I

P-rLi\sion

Et,PCN

+ R.

I t ,PI!

I’tLPCH:NR (3)

RII

+ T3t,P-

(4)

Phosphinyl radicals, obtained by hydrogen abstraction from dialkyl phosphites, have been trapped with t-nitrosobutane and the resultant nitroxyl radicals examined by e.s.r.l The reaction of phosphinyl radicals, e.g. ( 5 ) and (6), with olefins has been shown to occur with retention of configuration at p h o s p h o r u ~ . ~These - ~ ~ radicals have also been postulated as intermediates in the reactions of dialkyl disulphides and diary1 disulphides with pho~phinates.~-l~ From the reaction of diphenyl disulphide 0

0 I1 .I’

Pr’0‘‘I ‘1 1 MC

0

-

0

I1

/If,

p

priO.

hl c

--+

0 II

~ i ~ ~ p - l - t ~p,.iO../’\ iic

hl c

GH,5

(6)

’ lo

W. Hewerston and I. C. Taylor, J . Chem. SOC.( C ) , 1970, 1990. T. Saegusa, Y. Ito, N. Yasuda, and T. Hotaka, J . Org. Chem., 1970, 35, 4238. G. R. Van den Berg, D. H. J . M. Platenburg, and H. P. Benschop, Chem. Conim., 1971, 606; H. P. Benschop and D. H. J. M. Platenburg, Chem. Comm., 1970, 1098. L. P. Reiff and H . S. Aaron, J . Amer. Chem. SOC.,1970, 92, 5275. W. B. Farnham, R. K . Murray, and K. Mislow, Chem. Comrn., 1971, 146. W. B. Farnham, R. K. Murray, and K. Mislow, Chern. Cornm., 1971, 605.

232

0rganophosphor11s Chemistry

it appears that the reaction with thiyl radicals also occurs with retention at phosphorus.8 Since the products from reaction of phosphinyl radicals with olefins can be correlated with those from reaction of dialkyl phosphites with disulphides, e.g. (7), by means of a Grignard reaction it follows that this latter reaction occurs with retention of configuration at phosphoru~.~1 lo 0 P

RO"j '€1 Me

0

0 II

II

R'S'

1'

RO,.l

hl c

II

R' S S I 200nm) gives products derived by paths A and B.25 The mechanisms of formation of other isolated products, e.g. ethyl phenylacetate and biphenyl, are not so obvious. The relative efficiency of the two reaction paths is solvent dependent, path B being favoured by solvents of low polarity. Irradiation and thermolysis of the quinquecovalent phosphine (33) result in the elimination of triphenylphosphine.2s The azido-phosphetan oxide (34) gives both ring-expansion and ring-cleavage products on p h o t o l y ~ i s . The ~ ~ two ring-expansion products (35) and (36) are obtained in about equal yield. If the reaction is occurring via a nitrene intermediate, it is peculiar that there is little preference for the migration of the tertiary carbon atom compared with the primary carbon atom. 22

23 24 26

*II 27

G . MBrkl, F. Lieb, and C. Martin, Tetrahedron Letters, 1971, 1249. G . MBrkl and A. Merz, Tetrahedron Letters, 1971, 1269. A. N . Hughes and C. Srivanavit, Canad. J . Chem., 1971,49, 874. Y . Nagao, K. Shima, and H. Sakurai, Tetrahedron Letters, 1971, 1101. T. J. Katz and E. W. Turnblom, J . Amer. Chem. SOC., 1970, 92, 6701. M. J . P. Harger, Chem. Comm., 1971, 442.

Radical, Photochemical, and Deoxygeriation Reactions

1’11

237

238

Orgutlophosphorits Chemistry

2 Desulphurization and Deoxygenation Reactions

Dialkyl thiosulphonates (37) are desulphurized by tris(diethy1aniino)phosphine to give sulphoxides.28 In some cases sulphinate esters are formed as minor products. Diary1 thiosulphonates gave 1 : 1-adducts of the type (38). Desulphurization of sulphenimides (39) by tris(dimethy1amino)phos-

ii

ii

(37)

phine has been used as a method for the conversion of thiols into alkyl arnines.2g Deoxygenation of sulphenate esters, derived by reaction of (39) with alkoxides, with trialkylphosphines gives sulphides.sO Surprisingly, this reaction is not affected by the use of alcohols as solvents and intermediate (40) is thought to exist as a tight ion-pair. This contrasts with the previous finding that the intermediate (41), produced in the reaction of

30

D. N. Harpp, J. G. Gleason, and D. K. Ash, J . Org. Chern., 1971, 36, 322. D. N. Harpp and B. A. Orwig, Tetrahedron Letters, 1970, 2691. D. H. R. Barton, G. Page, and D. A. Widdowson, Chern. Comni., 1970, 1466.

RCtdicul, Photo diemical, rmd Deoxyget ICI t io ti R ca c t iot is

239

+

(Mc,N),P S K s I< (41)

dialkyl disulphides with tris(dimethylamino)phosphine, exists as a dissociated phosphoniuni salt rather than as a tight ion-paira31 The fact that trialkyl phosphites deoxygenate sulphenates to give thiols has been used to show that the penicillin derivative (43) is produced from (42) by a thermal sigmatropic shift.32

ot1 I

\

'-I

(43)

Desulphurization of the disulphide (44) has been shown to result in epimerization at the asymmetric carbon Synthetic applications of

31 33

53

D. N. Harpp, J. G . Gleason, and J. P. Snyder, J . Arner. Chem. SOC.,1968, 90, 4181. L. D. Hatfield, J . Fisher, F. L. Jose, and R. D. G . Cooper, Tetrahedron I>etters, 1970, 4897; R. D. G. Cooper and F. L. Jose, J . Amer. Chem. SOC., 1970, 92, 2575. S. Safe and A. Taylor, J . Chem. SUC.(C), 1971, 1189.

240


desulphurization reactions include the formation of the thietone (46) from (45) 34 and of olefins from oxathiolan-5-ones (47) 35 and azo-sulphides, r.g. (48).36 For reaction with oxathiolan-5-ones to be effective, the R

groups have to be aryl, presumably because they facilitate the loss of carbon dioxide. The thiepin (49), a stable 877 system, is desulphurized on heating with triphenylphosphine to give (50).37

34

s5

:Ii

A . Padwa and R . Grubber, J . Org. C‘hciri., 1970, 35, 1781.

D. H . R. Barton and B. J. Willis, Chenr. Conrni., 1970, 1225. D. H. R. Barton, E. H. Smith, and B. J. Willis, Chem. Comm., 1970, 1226. J . M . HofTmann and R. H . Schlessinger, J . Amer. Chem. Soc., 1970, 92, 5263.

Ph,P

R

(51)

I

R'

=

allql or aryl

XNHCHCo2H rc'action B

spy

Y =

protecting group

R1 + I Ph,POCO*CHNHX

(51)

+ PgS-SPY +Ph,PSPy

+ (51)

I

R

I

0

I1 II R'OP-0-P-OR I I OH OH

0

R I XNHCHCO-NHCHCO, Y

reaction A

4-

Ph,PSPy

0

I1 ROP(OH); ~

0

OH

I

II R'OP-OR

0

It Ph,POP(OH) OR

+

$

b

>

242

Or~nrtophosphorirsChemistry

The reaction of dipyridyl disulphide with triphenylphosphine to give the stable phosphonium salt ( 5 1) has been used in new methods of phosphorylation (reaction A),3Hin peptide synthesis (reaction B),39and in the formation of active esters of or-amino-acids (reaction C).40 These reactions appear to have synthetic potential. The deoxygenation of peroxycarbonates (53) with phosphines and phosphites has been e x a n ~ i n e d Reaction .~~ with phosphites favours pyrocarbonate formation (Path A) whilst phosphines favour carbonate formation (Path B). Secondary phosphine oxides are oxidized to phosphinic acids by perbenzoic acid.42 The kinetics of the deoxygenation of hydroperoxides by triphenylphosphine have been examined and the reaction shown to be catalysed by strong R'OCO*OCR'

I/

I1

-

0 0 S -= R or RO \\,here K alkyl or nryl T

x $1'

0

I1 X,PO-C,-O~* 4-

\

d X,P=O

.A ; ; , ' 6: - - -'I3

Rl

~

I1

+

R'OCOCORl II It

0 0

0

(53)

R'OCOR' I1

0

+ CO,

+ X,PO

There is a continuing interest in the use of phosphite-ozone adducts as sources of singlet oxygen and as reagents for mimicking the reactions of this species. The commercially available phosphite (54) forms an ozone adduct of striking stability.44 Decomposition of the adduct only becomes appreciable at temperatures > 0 "C; the decomposition exhibits first-order kinetics, so that at 10 "C k = 9.10 x niin-' and t i = 76.2 min. These

3R

38 40

4a 43 44

T. Mukaiyama and M. Hashimoto, Bull. Chern. SOP.Japan, 1971,44, 196; Tetrahedron Letters, 1971, 2425. T. Mukaiyama, R. Matsueda, and M. Suzuki, Tetrahedron Letters, 1970, 1901. T. Mukaiyama, K . Goto, R. Matsueda, and M. Ueki, Tetrahedron Letters, 1970, 5293. W. Adam and A. Rois, J . Org. Chern., 1971, 36, 407. R. Curci and G. Modena, Tetrahedron, 1970, 26, 4189. R. Hiatt and C. McColeman, Cunud. J . Chern., 1971, 49, 1712. M. E. Brcnnan, Chern. Cornm., 1970, 956.

Rndicnl, Pliotocliemicnl, nnd Deoxygeriotion Renctions

243

values differ considerably from those for the triphenyl phosphite--oLone adduct, k = 1.47 n1in-l and t i = 0.47 niin at 10 " C . Decomposition of the adduct in the presence of tetraphenylcyclopentadienone gives products typical of the intermediacy of singlet oxygen. Reaction of the triphenyl phosphite-ozone adduct with cis- and trans- 1,2-diethoxyethylene has been shown to give a mixture of 1,2-dioxetans of very similar omp position.^^ Since the starting olefins are not isomerized under the reaction conditions, isomerization is proposed as occurring in intermediates ( 5 5 ) and (56). The

+

I

OEt (55)

+

p-(O El0

qO-[ +-

OEt

OEt 1 7(':,

0-0 EtO *on

(56)

83:;

efficiency of rotational equilibration would be hard to rationalize on the basis of a single 1,4-biradical or 1,4-dipolar species. Dialkyl disulphides are oxidized to thiosulphinates and thiosulphonates by the triphenyl phosphite-ozone adduct at temperatures below that required for singlet oxygen formation, and therefore it is probable that this reaction also involves ionic interrnediate~.~~ Trifluoroethanol has been shown to promote the addition of nitrenes, generated by the reaction of nitroso-compounds with phosphites, to aromatic hydrocarbons, e.g. (57), (58), and (59) are formed from the reaction

(57)

(58) 3-

yH,NHPh

46

4e

A. P. Schaap and P. D. Bartlett, J . A m w . Chem. Soc., 1970, 92, 6055. R. W. Murray, R. D. Smetana, and E. Block, Tetrahedron Letters, 1971, 299.

244


of nitrosobenzene with triethyl phosphite in the presence of mesitylene and the Reaction of nitroso-compounds with phosphites in alcoholic solutions containing acid gives products derived by reduction of the nitroso-group and substitution of the alcohol into the aromatic ring.** It is suggested that reaction occurs via an intermediate of the type (60). This may either be protonated, eventually to yield substitution products, or else decompose to give a nitrene. Kinetic measurements of the reaction of triethyl phosphite with a variety of substituted nitrosobenzenes have been made4e and these indicate that the rate-determining step is nucleophilic attack of the phosphite upon the oxygen atom of the nitroso-group to give an intermediate like (60). L

t

H NOP(0 K )3

The kinetics of formation of phosphonates by reaction of o-dinitrobenzene with phosphites have been examined.60 The energy of activation for the reaction increases as the nucleophilicity of the phosphite decreases, e,g, ethyl diphenylphosphinite 14 kcal mol-l, diethyl phenylphosphonite 16 kcal mol-I, and triethyl phosphite 21 kcal mol-I. An intermediate of the type (61), formed by nucleophilic attack of the phosphite, was proposed. In (61) there is a particularly favourable electrostatic interaction. That p-dinitrobenzene is unreactive, is thought to stem from the fact that this compound cannot form an intermediate with such a stabilizing factor. It has been pointed out,61 in the full paper describing the formation of (64) by deoxygenation of the nitrobenzoxazole (62), that the reaction can be rationalized in terms of an intermediate nitroso-compound (63) or compound (65). Further synthetic applications of the deoxygenation of nitro-compounds have been described, e.g. the syntheses of (66) 62 and (67).63 There has been " " 4s 6o 61 62

63

R. J. Sundberg and R. H. Smith, Tetrahedron Letters, 1971, 267. R. J. Sundberg and R. H. Smith, J . Org. Chem., 1971, 36, 295. R. J. Sundberg and C.-C. Lang, J . Org. Chem., 1971, 36,300. J. I . G . Cadogan and D. T. Eastlick, J . Chem. SOC.(B), 1970, 1314. A. J. Boulton, I. J. Fletcher, and A. R. Katritzky, J . Chem. SOC.( C ) , 1971, I 93. K. E. Chippendale, B. Iddon, and H. Suschitzky, Chem. Comm., 1971, 203. J. I. G . Cadogan, R . Marshall, D. M . Smith, and M. J.Todd,J. Chem. SOC. ( C ) , 19 0,244 I .

Radical, Photochemical, and Deoxygenation Reactions

245

I

R

9

246


I! (67)

further interest in the rearrangement reactions which take place on the formation of phenothiazines by cyclization of nitrenes derived from 2-nitrophenyl phenyl sulphides, e.g. in the formation of (68) and (69).54*66 0M c

o.2Me

-xz-+ /

'N: 0' Mc

,.'

../' J 0@I-

;,

I

bhlc

(69) b4 65

J . I. G . Cadogan and S. Kulik, Chem. Cotnm., 1970, 792. J . 1. G . Cadogan, S. Kulik, C. Thomson, and M. J. Todd, J . Chem. Soc. (C), 1970, 2473.

Rriclictrl, Plioroclieaiictrl, arid Deoxygencrtion Reactions

247

The efficient conversion of the furazans (70) into 1,4-dinitriles (71) is thought to occur #in the nitrile oxides (72).6s Thermal decomposition of the diaziridones (73) in the presence of triethyl phosphite gives the phosphine-imine (75) and the isocyanate (74), which subsequently react together to give the carbodi-imide (76).67

0 I1 C /\

IIN-N-R

(73)

6E G7

(EtO),P __J

RNCO (74)

+

(EtO),P=NR (75)

T. Mukai and M . Nitta, Chent. Conim., 1970, 1192. F. D. Grecne, W. R. Bergmark, and J. F. Pnzos, J . Org. Chem., 1970, 35, 2813.

1I Physical Methods BY J. C. TEBBY

As in previous volumes, the abbreviations PI1', PIv, Pv, efc. refer to the co-ordination number of phosphorus. Where convenient the compounds in each section are dealt with i n this order. A number of theoretical studies such as MO calculations are briefly discussed. They are placed in the sections where they are of most relevance.

1 Nuclear Magnetic Resonance Spectroscopy

The 31P chemical shifts (6,) are relative to 85% phosphoric acid.

A. Chemical Shifts and Shielding Effects.-Semi-empirical SCF-CI calculations of net charges for methyl and ethyl primary, secondary, and tertiary phosphines correlate well with experimental values of 6p.l The shielding effects of para-orientated substituents on the arylphosphine series ( l ) , (2), and (3) showed some interesting trends2 Whilst fluorine showed the strongest shielding effect of the halogens, electron-donating groups increased the shielding still further. This has been interpreted as the direct operation of a mesomeric effect increasing p,.,-d,, conjugation. Another phosphine system (4;R = Ph or OMe, Y = CI or OMe) has been ~ t u d i e d . ~ The large difference in the type of substituent makes it difficult to distinguish inductive and mesomeric effects on 6p.*

The reverse mesomeric effect (p,-p, conjugation) is believed to be very favourable in the A2-phospholen system (5).4 Compared with the corresponding A3-phospholens (6), the conjugated system ( 5 ) shows both Y and the phosphorus atom to be deshielded, and the vinyl proton is shielded. The cyclic nature of the molecule is important because the analogous R. Friedemann, W. Gruendler, and K. Issleib, Tetrahedron, 1970, 26, 2861. H. Goetz, H. Hadamik, and H. Juds, Annulen, 1970, 737, 132. A. Schmidpeter and W. Zeiss, Chem. Ber., 1971, 104, 1199. L. D. Quin, J. J. Breen, and D. K . Myers, J . Org. Chern., 1971, 36, 1297. *Throughout this chapter, where X, Y, etc. are not specified, they may be taken as representing any of a variety of groupings, e.g. halogen, alkyl, alkoxy, ptc.

a

Physical Methods

249

acyclic vinylphosphines do not show these effects. It is possible that part of the cause of the differences between the series ( 5 ) and ( 6 ) may be a shielding effect in the latter compounds (see Section 7 for discussion of stereochemical differences). Such a shielding effect (of the order Sp 2- 6 p.p.m.) has been observed for the allylic compounds (7, Y = NMe,, OPr’, or CI).s

(5)

(6)

(7)

Bulky groups tend to have a deshielding effect on SP for phosphines. Further examples have been reported.0 The effect can be considered to be opposite to the increase in electron lone-pair s-character which is produced by angular restraint,’ i.e. the bulky groups tend to increase the bond angles and increase the p-character of the electron lone-pair. The substituted trisanisylphosphines (8) show interesting differences in 8p according to the orientation of the methoxy-group in each ring.s In accordance with the mesomeric effects noted above,2 the ortlto- and para-isomers show the largest shielding of the phosphorus atom but the extra large shielding effect observed for the ovtho-isomer (where steric and inductive forces should be inducing a deshielding effect) may be due to an anisotropic effect by a methoxy-group. Further efforts have been made to produce one set of parameters which can estimate Sl. for phosphines and phosphonium salts.s The group contribution depends on the number of /land y carbon atoms, but extra shielding by phenyl and allyl, benzyl, or cyclohexyl groups has to be taken into separate account in the equation.

(8)

The chemical shifts, Sp, of substituted arylphosphonic acids (9) have been found to be linearly related to the Hammett 0 and Taft ult and 01 parameters.@ The shielding of the phosphorus nucleus increases with the electron-withdrawing properties of the substituents, which is analogous

a

A. I. Razumov, B. G. Liorber, T. V. Zykova, and I. Ya. Bambushek, Zhur. obshchei. Khim., 1970, 40, 1704. S. 0. Grim, A. W. Yankowski, S. A. Bruno, W. J. Bailey, E. F. Davidoff, and T. J. Marks, J. Chent. and Eng. Data, 1970, 15, 497. ‘Organophosphorus Chemistry’ (Specialist Periodical Report), ed. S. Trippett, The Chemical Society, London, 1971, Vol. 2, Chapter 1 I . S. 0. Grim, E. F. Davidoff, and T. J. Marks, Z . Natrrrforsch., 1971, 26b, 184. C. C. Mitsch, L. D. Freedman, and C. G . Morcland, J . Mngn. Resoric~nce,1970, 3, 446.

250

Orgnnophospiror~sChemistry

to the previously observed effect of fluorine substituents.I0 It appears therefore that electron-withdrawing groups in general tend to shield tri-, tetra-, and penta-co-ordinate phosphorus atoms, probably by increasing p,,-d, conjugation. I t is of interest that M O calculations on F3P0 indicate that P - 0 n-bonding tends to block P-F bonding and this results in an increase in the (T character as well as the creation of some T character of the P-F bond.ll When the phosphorus atom bears a group which normally shows appreciable d,-p, bonding, e.g. the oxyanion of phosphonic acids or the sulphur atom in (lo), it is possible for electron-donating groups on the aryl ring to have a deshielding effect because they reduce P=O or P=S p,-d, bonding.12 In these cases substituents which act mesonierically with the phenyl ring have the strongest effects. An effort has been made to calculate Sp non-empirically for a wide series of fluoro- and chlorophosphoryl compounds, with varied degrees of success.13

(9)

In a study of cyclic phosphoniuin salts14 it was found that, compared with acyclic compounds, a six-membered ring, as in ( l l ) , had a marked shielding effect on the phosphorus nucleus whereas a five-membered rjng had a deshielding effect. Thus relatively small deviations from tetrahedral arrangement produce a shielding effect whereas a deshielding effect is predominant when there is gross distortion of the bonds. The sensitivity of to d-orbital occupation is demonstrated by a series of alkylidenephosphoranes ( I 2).15 Shielding increases with the increase of electrondonating power of the C,-substituent (see Table I ) but decreases with increase of the electron-donating power of the P-substituents, i.c. in the order Me,P < Et,P < Pr3P.

Table 1 Phosphorane

8P lo

ll

l2 la l4

Is

Et,P=CH, - 23.6

Et,P=CHMe - 16.9

Et,P=CHEt - 14.8

E:t,P=CHPr - 14.6

‘Organophosphorus Chemistry’ (Specialist Periodical Report), ed. S. Trippett, The Chemical Society, London, 1970, Vol. 1, Chapter 11. F. Choplin and G . Kaufmann, Bull. SOC.chitti. France, 1971, 387; F. Acloquc, 0. Kahn, and A. Dniestrowski, Cotnpf. rend., 1970, 271, C, 1062; I. Absar and J. R. Van Wazer, J . Phys. Chew., 1971, 75, 1360. H . Goetz, H. Hadamik, and H. Juds, Annalen, 1970, 742, 59. A. Mueller, E. Niecke, R. Kebabcioglu, and R. Schmutzler, 2. Chent., 1970, 321. D. W. Allen and J. C. Tebby, J . Chem. SOC.( B ) , 1970, 1527. R. Kmtcr, D. Simic, and M . A. Grassbergcr, Annulen, 1970, 739, 21 1 .

Physical Methods

25 1

c

-

A series of iminophosphoranes (13) has been studied in detail.Ig The strong electron-withdrawing P-substituents were expected to encourage occupation of a second phosphorus d-orbital, i.e. overlap of the sp2 nitrogen lone electron pair with the d,, and dxs-vaorbitals of phosphorus, as shown in (14). Variation of R produced a very wide range of shifts from a 6 r value of - 28 for (13, R = H) to + 36.5 for (13, R = c-C,H,,). There c was also a decrease in the PN bond moment and an increase in v p ~ upon increasing the electron-donating power of R. Values of 6p for iminophosphoranes with phosphorus and silicon substituents and for cyclic derivatives (1 5 ) Is have also been measured. Me

c1,c

C13C

\

\-

C1--P EN, C1,C

R

/

-c

Cl-PEN-R /

C13C

(14)

(13)

Me (15)

The 31P n.m.r. parameters have been tabulated for a wide range of Prll amino-compounds 21 and Pv compounds.21 The value of aP for compounds with four P-N bonds correlates with the hybridization of the nitrogen atom,22moving to higher field in the order p 3 .c sp3 < sp2 < sp. In contrast to the phosphines, the effect of angular restraint in phosphites is to cause shielding (see Table 2).23 However, the effect is not continuous because 8 p decreases again when the restraint is severe. Possibly the increase in d-orbital occupation upon angular restraint goes through a maximum. 2op

Table 2 Phosphite SP

l8 2o 'L1 22

23

P(OEt), - 137

P(OCH,),CMe

- 91.5

/O\ P(OCH,),CH - 105

E. S. Kozlov, S. N. Gaidamaka, Yu. Ya. Borovikov, V. T. Tsyba, and A. V. Kirsanov, Zhur. obshchei Khim., 1970, 40,2549. A. Schmidpeter and H. Rossknecht, 2. Nufurforsch., 1971, 26b, 81. 0. J . Scherer and W. Gick, Chem. Ber., 1971, 104, 1490. A. Schmidpeter, H. Rossknecht, and K . Schumann, Z . Nururforsch., 1970, 25b, 1182. R. Burgada, Bull. SOC.chim. France, 1971, 136. D. Bernard and R. Burgada, Cornpi. rend., 1970, 271, C, 418. A. Schmidpeter and K. Schumann, Z . Nuturforsch., 1970, 25b, 1364. R. D. Bertrand, J. G. Verkade, D. W. White, D. Gagnaire, J. B. Robert, and J. Verrier, J . Mngn. Resonunce, 1970, 3, 494.

252


The 31Pchemical shifts for P-F compounds have been reviewed.24 The compounds differ from most other organophosphorus compounds because 8p becomes more positive as the electronegativity of the atoms attached to phosphorus increases. The effect is at a maximum for P"l compounds. They behave normally with regard to an increase in shielding with increase in co-ordination number and therefore the PI1' compounds are the least shielded. Thus the largest negative values ( - 190 to - 250) are observed for compounds of the type YPF,. With the new value of aP of 80 for PF,, the variation of 8p with the number of fluorine atoms in Pv compounds is now shown to be fairly consistent. The value of 8p has also been reported for a series of aminohalogeno Pv c o m p ~ u n d s26. ~ ~ ~ The relative insensitivity of aP to changes in electronegativity of substituents which is observed for Pv fluoro-compounds ,* is also evident for penta-arylphosphoranes. Thus the placement of para-substituents on the phenyl rings of pentaphenylphosphorane has very little effect and 8p is + 88 f 1 p.p.m. for (16; Y = H, Me, or Cl).27 The effect on 81, of the introduction of an amino-group in the bis-biphenylenephosphorane system ( I 7) is similar to that of an alkyl group (see Table 3).28

+

Table 3 Compound

8I'

17,Y = H + 112

17,Y = Me 97

+

1 7 , Y = NH, 92

+

1 7 , Y = Bu 90

+

17,Y

=

+ 85

Ph

The leF n.m.r. spectra of the Pv compounds (18) indicate that the PAr,(OEt), group has very weak electron-withdrawing properties both inductively and mesomerically.2u This is to be contrasted with (19) where the PF, group was found to be the most strongly withdrawing group in a range of P1ll,PIv, and Pv compounds. This more recent result shows that 24

*s 28

27

2B

G . S. Reddy and R . Schmutzler, Z . Natiirforsch., 1970, 25, 1199. G . I . Drozd, M . A. Sokal'skii, 0. G . Strukov, and S. Z . Ivin, Zhrrr. obshchei Khim., 1970, 40, 2396. S. C. Peake, M . J. C. Hewson, and R . Schmutzler, J . Chern. SOC.( A ) , 1970, 2364. M . Schlosser, T. Kadibelban, and G . Steinhoff, Annalen, 1971, 743, 25. D . Hellwinkel and H. J . Wilfinger, Annalen, 1970, 742, 163. B. C. Chang, D. Z. Denney, and D. B. Denney, J. Org. Chern., 1971, 36, 998.

253

Pliysical Methods

the large CJR effect in (19) is triggered by the large inductive effect of the fluorine atoms on phosphorus. F

F

Some interesting shielding effects have been reported for the substituted A3-phospholen (20).30 The shielding effect of a P-phenyl group on the a-methyl group shifts 7hIe from 8.83 in (20, Y = :) to 9.29 p.p.m. in (21, Y = :). The oxide shows a similar effect. On the other hand, the P-benzyl group in the salts (22, R = Me) and (22, R = Ph) can achieve a conformation in which the phenyl group shields the vinyl protons so that they appear at T 4.2. The a-methylene protons of the P-chloro- and P-bromoderivatives of A3-phospholens are at unusually low field, and their equivalence suggests that there is loss of configurational integrity at phosphorus.gl Cooling or dilution in hexane raises the chemical shift and produces a multiplet signal. These results are consistent with a rapid intermolecular halogen exchange reaction.

Y

The 'H chemical shifts of the P-H group have been tabulated for 150 Like many other heteroatom-bound protons, the chemical shift range is large (7 0 -12 p.p.m.). In this case shielding of the proton increases with decrease in co-ordination number at phosphorus. The 30

31

L. D. Quin and T. P. Barkett, J . Anter. Cheni. SOC.,1970, 92, 4303. D. K. Myers and L. D. Quin, J . Org. Chem., 1971, 36, 1285. D. Houalla, R. Marty, and R. Wolf, 2. Nntrrrforsch., 1970, 25b, 451.


2 54

presence of P-aryl groups causes deshielding of the proton, as does its attachment to a phosphonium centre.33 There is an upfield shift upon dilution (AT 0.2 p.p.m.) which is intermediate between that (AT 0.05 p.p.m.) for SiH and that (AT 0.5 p.p.m.) for SH. This trend also parallels the hydrogen-bonding abilities of the groups. 31P N.m.r. studies are reported on the triethylphosphine 34 and trisdimethylaminophosphine 35 complexes with boron halides, and triethylphosphine complexes with aluminium chloride.3s A correlation of aP with the number of phosphorus ligands in metal carbonyl complexes has led to a qualitative rationalization of 8p in terms of u- and ~ b o n d i n g . ~ '

B. Studies of Equilibria and Reactions.-N.m.r.

spectroscopy is being increasingly employed to study the mode and course of reactions. Thus 31P n.m.r. has been used to unravel the mechanism of the reaction of phosphorus trichloride and ammonium chloride to give p h o ~ p h a z e n e s , ~ ~ and to follow the kinetics of alcoholysis of phosphoramidite~.~~ Its use in the study of the interaction of nucleotides and enzymes has obtained valuable information on binding sites and conformations 40 and work on the line-widths of the 31Presonance has enabled the calculation of dissociation rate-constants and activation energies to be p e r f o ~ r n e d . ~ ~ lH N.m.r. spectroscopy has been used to identify phosphorus pesticides 4 2 but the complexity of the spectra would make it difficult to analyse mixtures. 31P N.m.r. spectroscopy is better adapted to this task, especially when the compounds differ in the groups immediately attached to phosphorus. Thus 81, values of the commonly used pesticides fall into eight well-separated regions (see Table 4).43 It is also possible to estimate the chain length of linear polyphosphates using 31P n.m.r. The P,, P,, and P6-80 middle 22 p.p.ni. respectively, whilst phosphate groups have aP + 19, + 21, and 5, + 8, + 9 and the PZp3, P,, Po, and P,o end-groups give peaks at + 10 p.p.m. re~pectively.~~ The 6p values also depend upon the p H of the solution. This method has also been used for the direct determination of

+

33

s4 56

s6 s7

s*

40

" 42

'' 44

+

J. R. Cortield, M . J . P. Hargcr, R. K . Oram, D. J . H . Smith, and S. Trippctt, C ' h t t i . Corntn., 1970, 1350. G . Jugie, J . P. Laussac, and J. P. Laurent, B i d . SOC.chim. Fruticc.. 1970, 2542. G . Jugie, J. P. Laussac, and J . P. Laurent, J . Inorg. Nuclear Chem., 1970, 32, 3455. W. H. N. Vriezen and F. Jellinek, Rec. Trm. chim., 1970, 89, 1306. R. Mathieu, M. Lenzi, and R. Poilblanc, Inorg. Chem., 1970, 9, 2030. J. Emsley and P. B. Udy, J . Chem. Soc. ( A ) , 1970, 3025. E. E. Nifant'ev, N. L. Ivanova, and A. A. Borisenko, Zhur. obshchei Khirn.,1970,40, 1420. D. H. Meadows, G. C. K . Roberts, and 0. Jardetsky, J . Mol. Bid., 1969, 45, 491. G . C. Y . Lee and S. I. Chan, Biochetn. Biophys. Res. Cotnm., 1971, 43, 142. L. H. Keith, A. W. Garrison, and A. L. Alford, J . Assoc. Offir. Atrn1J.t. Chetnists, 1968, 51, 1063; H . Babab, W. Herbert, and M . C . Goldberg, AnnlJIt. Chint. Actn, 1968, 41, 259; L. H. Keith and A. L. Alford, ihid., 1969, 44, 447; L. H . Keith and A . L. Alford, J . Assoc. Ofic . Anolyt. Chemists, 1970. 53, 1018. R. T. Ross and F. J . Biros, Annlyf. Chittt. Acto. 1970, 52, 139. M . Kawabe, 0. Ohashi, and I. Yamaguchi, Blrll. Chern. Soc. Jrrprirl, 1970. 43, 3705.

Physical Methods

255

Table 4 Class of compound SP

Class of compound

Sr Class of compound SP

phosphates 6 + 3

phosphoramidates - 8

phosphoramidothioates -64+7 phosp horot ri t hioates - 118

phosphonates - 18

phosphorothioates -64+_3

phosphonothioates

phosphorodithioates

- 85

-95k3

phosphites - 140

linear phosphates in biological extracts,46and to distinguish phosphonates and phosphates occurring in lipid fractions.46 Metaphosphates gave separate signals with and without the addition of magnesium The stereospecific nature of the dehydration of 2-phosphoglycerate to give (23) was established after the assignment of the chemical shifts of HA and HB had been d e t e ~ m i n e d . ~ ~

A fluxional amido-salt (24), in which the y-nitrogen atom acts as an internal nucleophile, has been identified by variable-temperature n.m.r. s p e c t r o s ~ o p y . ~At ~ - 63 "C two methyl signals are observed, one a singlet, one a doublet (J = 11 Hz) whereas at + 60 "C there is only one signal, a doublet with J = 5.5 Hz (the average of the low-temperature coupling constants). The solvent extraction of organophosphorus compounds has also been studied by 31Pand 'H n.m.r.4e

C. Pseudorotation.-An alternative intramolecular exchange process to Berry pseudorotation has been suggested, which also occurs with conservation of angular momentum.60 It has been called a 'turnstile-rotation process' because it involves the rotation of an apical-radial pair of ligands 4.5

T. Glonek, M. Lunde, M. Mudgett, and T. C . Myers, Arch. Biochem. Biophys., 1971,

40

T. Glonek, T. 0. Henderson, R. L. Hilderbrand, and T. C. Myers, Science, 1970, 169,

47

M. Cohn, J. E. Pearson, E. L. O'Connell, and I. A. Rose, J . Amer. Chem. SOC.,1970,

142, 508.

192. 92, 4095. 48

T. Winkler, W. Von-Philipsborn. J. Stroh, W. Silhau, and E. Zbiral, Chem. Comm.,

49

A. M. Rozen, P. M . Borodin, U. I. Mitchenko, and Z . I. Nikolotova, Radiokhimiya, 1970, 12, 510. I. Ugi, D. Marquarding, H . Klusacek, G . Gokel, P. Gillespie, and F. Ramirez, Angeiv. Chrm. Inttmwt. Edn., 1970, 9, 725.

1970, 1645. 60

256

Organophosphorits Chemistry

in the opposite direction to a rotation of the remaining three ligands. The result is the same as that of Berry pseudorotation, i.e. interchange of apical and radial pairs of ligands. The turnstile rotation is believed to be the cause of the rapid positional exchange of the ligands about the phosphorus atom in (25); the exchange was indicated by its 'H and 19Fn.ni.r. spectra. The barrier to Berry pseudorotation and the turnstile rotation could be different for molecules such as dimethyl trifluorophosphorane ; however, it is claimed that the exchange process is intermolecular and has a very low activation energy,51a similar to that observed for difluorotrimethylphosphorane (26, R = Me). Details are reported for this latter compound. The spectrum was concentration dependent (second-order in phosphorane) and whereas PCH coupling was maintained upon raising the temperature or concentration, the FPCH coupling was lost. Also, an estimate of the coalescence temperature for the fluorine resonances (made from Jpp i n the instantaneous structure) agreed with that observed. More recently, the variable-temperature spectrum of (26, R = Me) was studied in a wide range of In tetramethylsilane the activation energy was 15 f 2 kcal mol-l, indicative of an intraniolecular exchange process in this solvent. Also, at high temperature J F ~= I 4(2J~,11 J I , - ~ I where I) F, = apical fluorine and F, = radial fluorine.

+

F

The orientation assumed by bulky groups is of great interest since i t would assist the assessment of steric effects in Pv molecules. The spectra of some t-butylfluorophosphoranes have been d e t e r ~ i n e d .The ~ ~ spectrum of t-butyltetrafluorophosphorane was unchanged down to - 100 " C , indicating rapid positional exchange (cf. PhPF4).10 Like other dialkyltrifluorophosphoranes, the t-butyl compound (26, R = But') exhibits two types of fluorine atoms in its 19F 1i.m.r. spectrum, with chemical shifts and coupling constants characteristic of one radial and two apical fluorine atoms. The character of the n.m.r. parameters of the tributyl derivatives also supports the presence of two apical fluorine atoms, which shows that 51

52

( a ) T. A . Furtsch, D. S. Dierdorf, and A . H . Cowley, J . Artrer. Cherir. S'oc., 1970, 92, 5759; ( h ) H . Dreeskamp and K . Hitdenbrand, Z . Nofurforsch., 1971, 26b, 269. M . Fild and R. Schmutzler, J . Cherji. SOC.( A ) , 1970, 2359.

any steric compression between the three t-butyl groups is not sufficient to displace fluorine from its apical orientation. Dynamic processes in fluorophosphoranes have been reviewed.53 Variable-temperature lH n.m.r. spectroscopy on the oxyphosphoranes (27) and (28) has shown that a t-butyl group has a thermodynamic preference for a radial o r i e n t a t i ~ n .Thus ~ ~ whereas pseudorotation between the isomers (28a) and (28b), which maintain a radial t-butyl group, is observed, the steric repulsion between the t-butyl group and the or-phenyl group in (27) is sufficient to destabilize the isomer in which these groups are crowded together, and consequently no pseudorotation is observed. Had it been energetically favourable for the t-butyl group to occupy an apical orientation, pseudorotation would still have been observed. Me

Ph

Ph

McCO

H OMC

* OMe

OMe

The possibility that small rings may be able to increase rates of pseudorotation was advanced in Volume 1 of these Reports.lO Recent results add weight to this suggestion. Thus fast pseudorotation is reported for (29) G 5 and (30).66As in the previous examples, the small rings haveidenticalatoms bound to phosphorus and two other atoms or groups are identical, both of which encourage competition for the electronically preferred orientations. The pseudorotation process for (30) which maintains the phenyl group in a radial orientation has a very low barrier. Above - 5 1 "C pseudorotation uia (31) also becomes allowed and above 30 "C pseudorotation vicr (32), which has the ring spanning both radial positions, is possible. In this case the attainment of axial orientations for the two electronegative ethoxygroups and a radial orientation for the phenyl group probably offsets some of the ring strain in (32). Similar observations were made on its isomer (33). The room-temperature lQFn.m.r. spectrum of (34) contains a doublet, indicating equivalence of the trifluoromethyl groups. This signal collapses upon cooling the sample, to give a spectrum corresponding to apical and radial trifluoronlethyl groups.57 The 'H n.m.r. spectrum is unchanged upon cooling, which supports the suggestion of formation of the structure shown in (34). 63

b4 66 68

67

S. C. Peake and R. Schmutzier. Colloq. l u r . Cent. Nat. Rech. Sci., 1970, 101. A. P. Stewart and S. Trippett, Chem. Cotnni., 1970, 1279. G. 0. Doak and R. Schmutzler, J . Cheni. SOC.( A ) , 1971, 1295. D. Z. Denney, D. W. White, and D. B. Denney, J . Amer. Chem. Sac., 1971, 93, 2066. R. G. Cavell and R. D. Leary, Chem. Cumtrz., 1970, 1520.

258


OEt

Ph

(30)

(31)

OE t .I.

I

(32)

(33)

(34)

36Cl Nuclear quadrupole resonance (n.q.r.) studies s8 on PhPCI, and Ph,PC13 indicated non-equivalence of the chlorine atoms. However, a more recent report6@states that the spectra of these compounds and PCI, all contain two signals corresponding to apical and radial chlorine atoms and that replacement of chlorine by phenyl occurs in the radial position. D. Restricted Rotation.-A study on solvent and stereochemical effects on the restricted rotation of the stabilized ylides (35) has shown 6o that although the cisoid ( 2 ) conformation (35a) is generally predominant there is an increase in the amount of the transoid (E) conformation (35b) as the size

(35a)

(35W

of the ester alkyl group increases. It also increases as the polarity of the solvent increases, especially if the solvent has hydrogen-bonding properties. When both effects are combined, e.g. (35, R = t-butyl) in methanolic solution, the spectrum shows a predominance of the transoid conformer. The results were rationalized in terms of increased solvation of the oxyanion. The absence of a rotational process for the y-conjugated ester group in (36) was confirmed by the lack of variable-temperature spectra for (37).61 That this is due to lack of rotation is supported by the low carbonyl frequency of the y-methoxycarbonyl group and the strong r,t~ 69

uo

M. Kaplansky, R. Clipsham, and M. A. Whitehead, J. Chem. SOC.( A ) , 1969, 584. V. I. Svergun, V. G. Rozinov, E. F. Grechkin, V. G. Timokhin, Yu. K. Maksyutin, and G. K. Semin, Izvest. Akad. Nauk S.S.S.R., Ser. khim., 1970, 1918. J. P. Snyder, Tetrahedron Letters, 1971, 215. N. E. Waite, J. C. Tebby, R. S. Ward, M. A . Shaw, and D. H. Williams, J. Chem.

SOC. (C), 1971, 1620.

Physical Methods

259

conjugational effects on the stereocheniistry in the crystal (see Section 7 of this chapter). Y

The extent of restricted rotation about the amide band of (38) was used to compare the electron-withdrawing process of phosphonium salts (38, Y = alkyl) and chalcogenides (38, Y = 0 or S) with the more conventional electron-withdrawing groups.sz These phosphorus groups were found to exert a - M effect comparable with that of a nitro-group. Restricted rotation has been observed in tris-o-tolylphosphine sulphide and selenide (39).'j3 The spectrum of the selenide shows two methyl environments in the ratio 2 : 1 at 30°C but the methyl signals of the sulphide resolved to this pattern only upon cooling the sample. The corresponding oxide and the parent phosphine showed only one methyl environment down to - 60 "C. X-Ray diffraction of the selenide showed that the methyl group on one aryl group is directly behind the phosphorus atom in the crystal, as shown in (39).

M'e (38)

(39)

E. Inversion, Non-equivalence, and Configuration.-The inversion of phosphines is much slower than that of amines, and optical isomers of dissymetric phosphines can be isolated. Studies of the factors which affect the rates of inversion are advancing our knowledge of inversion processes in general. Delocalization of the lone electron pair lowers the barrier to inversion, and one way of achieving this is to have a silicon atom bonded directly to the inversion centre, as in (40).64 The coalescence temperature of the two methyl signals from the isopropyl group showed A c t to be 18.9 kcal mo1-l. The suggestion that pn-dn conjugation is the dominant effect is supported by the slightly higher barrier (AG: 21.4 kcal mol-l) to 82

84

G. P. Schiemenz and G. Stein, Tetrahedron, 1970, 24, 2007. R. A. Shaw, M . Woods, T. S. Cameron, and B. Dahlen, Chem. and Itid., 1971, 151. R. D. Baechler and K. Mislow, J . Amer. Chern. SOC.,1970, 92, 4758.

260

Orgarzophosphoriis Chemistry

inversion for the corresponding germanium derivative (which involves the less effective 3p-4d .rr-orbital overlap). The lower electronegativity and absence of lone electron pairs also makes silicon more effective at lowering the inversion barrier than sulphur or phosphorus.

The non-equivalence of two atoms or groups in the close proximity of an asymmetric centre may vary with concentration, temperature, and solvent. When the asymmetry is provided by a PI'' atom, loss of nonequivalence may be due to (a) inversion at phosphorus, as above,G4 ( b ) conformational changes, e.g. the fluorine atoms in (41),G5or (c) an intermolecular exchange process at phosphorus. Some examples of this latter type have recently been uncovered in which the exchanging atom is chlorine or bromine. Thus the methyl signals of the isopropyl group in (42,Hal = CI) merge at 50 "C whereas in the corresponding P-F conipound (42, Hal = F) the non-equivalence persists on raising the temperature.ss There was no doubling of the N-methyl groups at low temperatures, which shows that there is free rotation about the P-N bond. When the asymmetric centre is on a carbon atom it is possible to observe nonequivalence of P-substituents, e.g. in (43).67

The non-equivalence of the ester protons in the monomethyl- and monophenyl-phosphinic ester function, as in (44, Ch = chalkogen), has been studied.68 Compounds of type (45) have some interesting stereochemistry. They are prepared from racemic secondary butyl alcohol, and the presence of three signals in the 31P n.m.r. spectrum confirms that the phosphorus atom is the centre of pseudo-asymmetry.G8 A 1 : 2 : 1 triplet is observed which is attributed to the presence of equal amounts of two rnem forms, (45) and (46),which have different values of 8p (outer peaks), and two racemic forms, (47)and (48),which have identical values of 8p (central peak). e6

e7

du

H. Goldwhite and D. G . Rowsell, J . Mol. Spectroscopy, 1968, 27, 364. J. E. Bissey, H. Goldwhite, and D. G . Rowsell, Org. Mugn. Resonatice, 1970, 2 , 81. R. Fields, R. N. Haszeldine, and J. Kirman, J . Chem. Soc. (C), 1970, 197. R. Marty, D. Houalla, R. Wolf, and J . Riess, Org. Magn. Resonance, 1970, 2, 141.

Pliysical M e tliods

26 I

c 11

When a second asymmetric centre is present in the molecule in addition to an asymmetric phosphorus centre, diastereomers are produced whose n.ni.r. parameters may be used to identify the configuration. The second asymmetric group may be an inherent part of the molecule, as in (49), or may be introduced in the alcoholic part of an ester or the counter-ion of a salt. Thus the POCH signals of the ( R ) p isomer in (49) are downfield by 2--3 Hz from those of the (S)p the doublet methyl signal of the isopropyl group of the phenylphosphinates (50) is downfield for the ( R ) l , e~inier,~O and in the phenylethylamine salts of thiophosphonates ( 5 1 ) the degree of non-equivalence of the P-methyl signal is related to its absolute c~nfiguration.~’ 0 II P - - - C6H1

”’/ \o JPCH21< 0 0

(49)

(50)

Mcnthyl

S II Mc-P-OR I + 0- N H , C H P h M e (51)

N.m.r. spectroscopy has played an important part in determining the stereochemistry of the 1,3-dioxaphosphorinanes (52). The presence of the saturated six-membered ring means that there are usually conformational effects to be unravelled before configurational assignments can be made. The chair conformation is generally d ~ m i n a n t . ’ Phosphorus ~ substituents which exhibit shielding effects show that in many PIr1phosphorinanes this has been used to establish substituent occupies an axial position 7 2 and L(the equatorial conformation of a t-butyl substituent at C(5).’, Even in PIv derivatives the isomer possessing the bulkiest P-substituent in an axial K . E. DcBruin and M. J . Jacobs, Clret)i. Con:t?i.,1971, 59. W. B. Farnham, R . K . Murray, and K . Mislow, Chem. Comtn., 1971, 146. M . Mikolajczyk, M. Para, A . Ejchart, and J. Jurczak, Cheni. Cotiim.. 1970, 654. i2 W. G. Bentrude and K . C. Yee, Tetmhedroti Letters, 1970, 3999; M . Haemers, I ( ~ I xthrough ) a P1”atom is also affected by the lone electron pair orientation, being larger when the protons and the lone electron pair are on the same side of the ring, as in (62). The geminal coupling constants, J l , c y ~ r A and JI>C-Qfor (63, Hal = F) are of the same sign (13.5 and 4.2 Hz) when there is free rotation about the P-N bond,6s whereas in the chloride (63, Hal = CI) rotation about the P-N bond is more restricted and the coupling constants are of opposite sign (26 and 3 Hz). (0)

2 J I m ( l ~ ~

H

The very large geminal coupling constant involving sp2 carbon atoms which is observed in compounds of the type (64) has been discussed previously (ref. 10, p. 298). The presence of a P-Cl group had its usual effect and increased the coupling constant. Thus Jpc-11 for (64; Y = CI) is 46.5 H z . ~ ‘The large magnitude of these interactions may also be connected with pn-pn conjugation, a suggestion which is supported by the large magnitude of this coupling in the heteroaromatic derivatives (65) g 1 and (66).e2 These geminal couplings are to be contrasted with those of vinyldialkylphosphines which are of a very low magnitude, 1---2 H z , ~(cJ~ 80

00

611 92

93

M. Sanchez, J. Ferekh, J . F. Brazier, A. Munoz, and R . Wolf, Roczniki Chem., 1971, 45, 131. J. P. Albrand, D . Gagnaire, M. Picard, and J . B. Robert, Tetrahedron Letters, 1970, 4593. T. H. Chan and L. T. L. Wong, Canad. J . Chern., 1971, 49, 530. F. Mathey and R. Mankowski-Favelier, Bull. Soc. chitn. France, 1970, 4433. G . Borkznt and W. Drenth, Rec. Trot.. chinr., 1970, 89, 1057.

Physical Methods

265

+

J P C ~ I I 1 1.74 Hz for trivinylphosphine). These fascinating changes were also discussed in Volume 2 of these report^.^

Y

I’ll

(6.1)

(65)

The sign of J f c ,for ~ ~I”” compounds of the type (67), although ncgative when Y i s alkyl, dimethylamino, or methoxy, appears to be positive when Y is fluorine or c h l ~ r i n e .However, ~~ there is little difference in the magnitude of these constants. The spectra of the corresponding vinyl compounds (68) are also reported.95 In this case the magnitude of Jp( 11 for the dichloroand dianiino-derivatives is very large (41.6 and 30.9 Hz respectively), which is well above the usual range of 5 --25 Hz (ref. 7, p. 254).

Accurate values of J P , - H for methylenephosphoranes are difficult to obtain because tvctns-ylidation tends to decouple the nuclei. The spectra of the ylides (69) and (70) indicate Jp(‘11to be 22 and 12.7 Hz respectively,06 which is consistent with the .rp2character of the carbon bonds (ref. 10, p. 296). Similarly, Jp(.rI in the cyclic salts (71) is also

+

Some interesting Pv compounds have been prepared. The value of 13 Hz for (72) gg and 11 Hz for (73) but increases to the range 15 -20 Hz for the fluorophosphoranes ( 2 6 ) and cyclic oxyphosphoranes such as (29).55

Jp(’1.1is

94

1’. N. Timofeeva, U . L. Kleirnan, and B. I . Ionin, Zhrtr. obshchei Khin!., 1970, 40, 1046.

m no

RN

T. N . Timofeeva, €3. V. Semakov, and B. I. Ionin, Zhrtr. obshchei Khim., 1970, 40, 1169. W. Malisch, D. Rankin, and H. Schmidbaur, Chem. Ber., 1971, 104, 145. M . L. Filleux-Blanchard, M. Simalty, M. Berry, H . Chahine, and H . M . Mebazau, Brill. SOC.chiin. Frorice, 1970, 3549. ’r.J. K a t ~and E. W. Turnhloni, J . A m v - . C/rc.ui. Sot.., 1970, 92, 6701.

266

Urganophosphorw Chemistry HH

OE t (73)

The vicinal coupling constants in phosphines depend not only on the angles subtended by the three bonds but also on the orientation of the lone electron pair. Change in the former is limited in cyclic phosphines such as (20, Y = :) and (21, Y = :) and the effect of the orientation of the lone electron pair can be distinguished. The PCCH, coupling is much larger when the methyl group and lone electron pair are cis. Thus in (20, Y = :) and the corresponding P-methyl compound, J ~ c c ' His, 17-18 Hz, whereas J p c , ; ~is , 10 Hz for the phosphines with the other c o n f i g ~ r a t i o n . ~ ~ The range of 3Jpn is 14-20 Hz for the tetraco-ordinate PIv cyclic derivatives (20 and 21, Y = Ch or R) and 15-24 Hz for the PIv-ethyl series of compounds (67) in which there are quite large changes in the environment of the phosphorus atom, e.g. from (67, Y = F) to (67, Y = alkyl). The magnitude of this parameter is slightly larger for the t-butylthiophosphoryl halides (74).88 When the vicinal coupling involves a Pv atom the magnitude of coupling is similar to PIv compounds, e.g. 3 J p ~= 16 Hz for (30) and 19 Hz for (73).66 The rapid pseudorotation reported for these compounds means that these values are the average of coupling through apical and radial bonds. S

II McSC-PXY (74)

Some high vicinal coupling constants have been reported for vinyl systems. The trans PC=CH coupling constants for (68, Y = NMe,) and (68, Y = CI) are 57.0 and 77.6 Hz respectively. This is well above the usual range (28-51 Hz).l09 loo The cis PC=CH coupling constants of (68, Y = NMe, or C1) were also high (28.7 and 35 Hz respectively) thus maintaining the usual ratio between the cis and trans constants. More n.m.r. studies on the trifuranylphosphine system are reported.lol The couplings to the ring protons are all positive whether the phosphorus atom is bound to the a or position of the furan ring.lo2 However, longrange coupling to the C(5)-methyl group of the series (75) is positive for the phosphine but negative for the PIv compounds. 99

loo

Io1 lo*

G. Huegele and W. Kuchen, Chem. Ber., 1970, 103, 2 8 8 5 . P. Taw and H. Weitkamp, Tetrahedron, 1970, 26, 5529. F. Taddei and P. Vivarelli, Org. Magn. Resonance, 1970, 2 , 319. H . J . Jakobsen and M. Begtrup, J . Mol. Spertroscopy, 1970, 35, 158; H . J. Jakobscn, ibid., 1971, 38, 243.

Physical Methods

267

The thiazole ring is not renowned for its ability to transmit coupling effects, and therefore the report that the phosphonium derivative (76) exhibits long-range coupling of the magnitude 5 J p ~ 4e Hz and 6 J p ~ 3e Hz is quite surprising.1o3 If the structure is correct, then presumably throughspace coupling to the C(4)-methyl and coupling transmitted through the lone electron pairs on sulphur to the C(3)-methyl could be invoked. hl e N 4

( u i ) J,ioc,,ri, JpIVcnII,and J,i.vr'fi. The variation of J ~ O C with H dihedral angle has been used by many workers to estimate the stereochemistry of phosphorus heterocycles such as the dioxapho~phorinanes.~~-~~ A comparison of the angular dependence of J P O ( ~in H PI" and PIv compounds has been made, based on the cyclic phosphite (77, Y = :) and the corresponding phosphate and thiophosphate (77, Y = Ch), for which the dihedral angles can be fairly accurately estimated.lo4 The coupling constant of the PVcompounds rose steadily from 0 Hz at 60" to 24 Hz at 180" whereas in the phosphites J p o c ~ was l ~ at its lowest magnitude (0 Hz) at 120°, rising to a maximum of 16 H z at 180". The effect of the nature of the phosphorus atom on PVOCH coupling in the acyclic compound (78) has been studied in detail.Io5 I t is found that the coupling increases with the number of electronegative substituents, the largest magnitude being 17.2 Hz for (78; Ch = 0, X = Y = CI). A correlation of a2 (a measure of s-character which is obtained from 'Jp(; = 500d Hz) withJpoc.Ilshowed that the increase is due to increased s-character. The coupling constants of the chalcogenides of (78) increased with the mass of the chalcogenide, i.e. 0 < S < Se. Since little change of s-character is expected in this series, a variation in d,,-pn bonding may be an important factor. Jt is interesting to note that the range of J L , O ( ' ~ for l freely rotating POCH groups is quite similar for P'" and PIv compounds, i.e. about 7-14 Hz.

In8

F. Zbiral, Tetrahedron Letters, 1970. 5107. I). W. White and J. G . Verkade, J . Magti. R~.coiiaiirc,1970, 3, 1 1 1. M. Kainosho, J . Phys. Chein., 1970, 74, 2853.

268

Orgatiuphosphorirs Chemistry

Protonation studies of diphenylphosphinic esters and amides show that i .crcascc upon protonation of the esters but that J ~ N ( -decreases H up,,ri protonation of the amides.lo6 Values of JPN(.II have been tabulated for a number of P I ' ' compounds.20~ 21 The cyclic aminophosphine (79) has all four J P S ( - Hconstants with the same sign, probably positive.lo7 Attachment of the proton to an sp2 carbon atom, as in (SO), does not enhance JpN('I[; in fact the reverse occurs.1o8 The PNPH coupling constant, which is 3-4 Hz for the acyclic phosphinimine (SI), is quadrupled (13-14 Hz) when the amino-groups are included in a small ring, as in (82).19

JIl,,

0

II

( E t O), I'

c 11

t1 I

N H C =C Ph

( M e,N )

I1 P H =N 1% 'I

I

hl e

(82) G. Relaxation Times, Paramagnetic Effects, and N.Q.R. Studies.-lH and 31Prelaxation studies of some arylphosphines indicate that both dipolar and spin-rotation interactions contribute to the 31P relaxation in PhzPCl and PhPCl,, the spin-rotation interaction being more important at high temperature^.^^^ As expected, spin-rotation relaxation (estimated to occur only above 400 " C )was not observed for Ph,P. The phenyl rotation must be restricted, for although a cogwheel concerted rotation is energetically possible, such perfectly geared rotation of rings is improbable. Spin relaxation times have also been used to study enzyme-inhibitor interactions.l1° The shifts produced by the addition of a paramagnetic complex have been used in the assignment of the aromatic protons in (83).11' Several 35Cc1 nuclear quadrupole resonance (n.q.r.) studies have been carried out on chlorophosphorus c o m p o ~ n d s5.9~ ~The ~ frequencies observed for phenyldichlorophosphine are similar to those of phosphorus lo6 lo7 Ion loo

P. Haake and I. Koizumi, Tetrahedron Letters, 1970, 4849. J. Devillers, J. Roussel, R. Bugada, and J. Navech, Buff. SOC.chitn. France, 1971, 676. A. Zwierzak and A. Koziara, Tetrahedron, 1970, 26, 3527. S. J. Seymour and J. Jonas, J. Chetn. Phys., 1971, 54, 487.

B. D. Sykes,J. Atner. C'hetn. Soc., 1969,91, 949; B. D. Sykes, P. G. Schmidt,andG. R. Start, J . Biof. Chctn., 1970, 245, 1180. J. C. Kotz and R. J. Humphrey, Znorg. Nuclear Chem. Letters, 1970, 6 , 827.

Physical Methods

269

trichloride. The p-chlorophenyldichlorophosphine (84) has an absorption frequency (35.018 MHz) corresponding to the chlorine atom on the phenyl ring, which indicates that the PClz group is electron-withdrawing.ll2 The variable-temperature n.q.r. spectrum of the phosphinimine (85) shows a change in the frequencies of the absorptions at about - 188 "C. This is probably related to a phase transition in which the lattice deformation alters N-S p,-d, bonding.l13

2 Electron Spin Resonance Spectroscopy The e.s.r. spectra of stable phosphorin radicals have been reviewed.l14 Radical anions may be formed from phosphines with or without P-C cleavage. The PIv radical (86) is easier to prepare than the nitrogen analogue. It has a spectrum in which the coupling to phosphorus is strongly temperature dependent, probably due to a variation of the geometry of the lone electron pair.l15 The n-spin populations indicate that the Me$ group is electron-attracting, probably due to p,-d, bonding. The spectrum of the radical (87), which is prepared from tris-a-naphthylphosphine, has also been described.l16

The e.s.r. spectrum of the phosphonium radical (88, Y = H) resembles that of Ph&H except that the splitting produced by the phosphorus atom is over three times that produced by the methine proton.l17 The spectrum of (88, Y = COMe) was also determined. The formation of the triradical 115 113

118 117

J. S. Dewar and M. L. Herr, Tetrahedron, 1971, 27, 2377. R. M. Hart and M. A. Whitehead, Mol. Phys., 1970, 19, 383. K. Dimroth, Colloq. Int. Cent. Nut. Rech. Sci., 1970, 139. F. Gerson, G. Plattner, and H. Bock, Helu. Chim. Acra, 1970, 53, 1629. M. H. Knoosh and R. A. Zingaro, J. Amer. Chern. Soc., 1970, 92, 4388. H. M. Buck, A. H . Huizer, S. J. Oldenburg, and P. Schipper, Rec. Trm. chirtt., 1970, 89, 1085.

270

0rganophosphor.us Chemistry

(89) was confirmed by e.s.r. studies on the solid and on a solution.l18 The spectra of phenacite 4-phosphate,llB thiophosphate,120 and vanadyl chloride-phosphine 121 radicals have also been described. Calculations on the hypothetical diradical (90) indicate that interaction with the d-orbitals on phosphorus could produce a singlet state.122

3 Vibrational Spectroscopy A. Band Assignments and Structural Elucidation.- The vibrational frequencies associated with the PF2 group 123 and PC12 group 124 in the i.r. and Raman spectra of the phenyl Pi" compounds are described and the band assignments for triphenylphosphine and its arsenic and antimony analogues are Reassignments of the deformation region for monosilylphosphines have been made.12s Depolarization data on trimethylphosphine oxide are now available and the relationship between the symmetric and asymmetric POP vibrations has been equated for diphosphates, and some halogen and metal salt derivatives.128 The polarization of a carbonyl group produced by its conjugation with an ylide causes a large decrease in V(Q. This shift to lower frequency is increased further when a double bond is interposed, lZ9 thus increasing the extent of The i.r. spectra of two crystal forms of aminomethylphosphonic acid (91) and its 15Nand 211analogues have been A Fermi resonance between Y Y ; H and vx1) vibrations and certain binary combinations can explain most of the spectra. The related aminophosphinic acid (92) and 11*

119

K. Leibler, K.Okon, and K. Checinski, J. Chirn. phys., 1970, 67, 746. M. C. R. Symons, J. Chern. Phys., 1970, 53, 857.

G. Lassmann, W. Damerau, K. Lohs, N. Klimes, and Z. Baldjeva, Z. Chem., 1970, 10, 297. lZ1 G. Henrici-Olive and S. Olive, Angew. Chetri. Internat. Edn., 1970, 9, 957. na R. Hoffmann, Accounts Chem. Res., 1971, 4, 1. l Z 3J. H. S. Green, D. J. Harrison, and H. A . Lauwers, Bull. SOC.chirn. helges, 1970, 79, 567. 1 3 p H. Schindlbauer and H. Stenzenberger, Spectrochim. Acta, 1970, 26A, 1707. l Z 6 A. H. Norbury, Spectrochitn. Acto, 1970, 26A, 1635. 126 J. E. Drake and C. Riddle, Spectroi.hirn. Acto, 1970, 26A, 1697. lZ7 J. H. S. Green and H. A. Lauwers, Bull. Soc. chint. belges, 1970, 79 571. lZ8 A. Muck and F. Petru, 2. Chenr., 1971, 11, 29. l m M. J. Berenguer, J. Castells, R. M . Galard, and M. Moreno-Manas, Tetrahedron Letters, 1971, 495. 1 3 0 C. Garrigou-Lagrange and C. Destrade, .I. Chini. phj.s., 1970, 67, 1646; C. Destradc and C. Garrigou-Lagrange, ibid., p. 2013.

27 I

PI1ysicnl Methods

its conjugate acid and base have been studied.131 The spectrum of the hydrochloride is typical of very strongly hydrogen-bonded systems, there being four very broad humps dominating the whole region from 200 to 3600 cm-l. The spectra of two amino-acids of the type (93) 132 and of some pyrimidylal kylphosphonic acids 133 are also reported.

+

I I3NCH,PO3H

Id NI PhCH,

(91)

C H-P I C3H,

0,I Ph

H + I Id3N-CMe2CH,O*PO2(93)

(92)

Metal-ligand vibrations have been identified using metal isotopes, e.g. the Ni-P stretching band which appears at 273.4 cm-1 for 68NiC1,(PEt3)2 is shifted to 267.5 cm-l for the s2Ni c0mp1ex.l~~ B. Stereochemical Aspects.-The i.r. spectrum of the bis-trifluoromethylphosphinite (94) has been determined in the gas, liquid, and solid phases.13K The doubling of the H or D bending and stretching bands is attributed to rotational isomerism, thought to arise from intramolecular hydrogenbonding and lone-pair repulsions, which gives a mixture of the conformers (94a) and (94b). 7r-Bonding in (99, and therefore the planarity of the NP3 skeleton, should be encouraged by electron-withdrawing substituents on the phosphorus atom. However, the i.r. and Raman spectra of (95) are difficult to explain convincingly on this basis and a pyramidal structure with a weak N-P bond is preferred.136 The stereochemistry of the phosphazenes (96) has been estimated from their vibrational

(95)

(94)

R. Tyka and H. Ratajczak, Bull. Acad, polon. Sci., SPr. Sci. chitn., 1971, 19, 21. J, Ferekh, A. Munoz, J. F. Brazier, and R. Wolf, Compt. rend., 272, C, 797. V. S. Reznik and Yu. S. Shvetzov, Izoest. Akad. Nnuk S.S.S.R., Ser. khim., 1970, 2254. l:le

K. Nakarnoto, Itwtritment News, 1970, 20, 1. R. C. Dobbie and B. P. Straughan, Spectrochim. Acfa, 1971, 27A, 255. P. J. Hendra, R. A. Johns, C. T. S. Miles, C. J. Vear, and A. B. Burg, Spectrachiin. Actri, 1970, 26A, 2169. D. P. Khomenko, G . ti. Dyadyusha, and E.S. Kozlov,Zhur.strukt.Khim., 1970,11,660.

272


The configuration of dioxaphosphorinanes (97) has been estimated from ~ p - 0 An . ~ equatorial ~ ~ P=O group usually gives a band at higher frequency than an axial P=O group. Absorption bands due to POC, PO, and PMe groups appear as doublets in the spectra of neat and dilute carbon tetrachloride solutions of methyl d i m e t h y l p h ~ s p h i n a t e . ~The ~ ~ changes in intensity with solvent and temperature indicate that the doubling is due to the existence of two conformations, the more stable one having bands at 1042, 1230, and 1310cm-l and the other at 1062, 1246, and 1300cm-1. The dipole moment in carbon tetrachloride indicates that the conformers are (98a) and (98b), the former predominating. The effect of orientation on v ~ for - cyclic ~ thiophosphates has also been briefly d i s c u s ~ e d14* . ~ ~The ~ i.r. and Raman spectra of the difluoro- and chlorofluoro-compounds (99, X = CI or F) are also compatible with the presence of two discrete conformers with nearly the same energy.141 Me I

Y

?/"\..

I

I

Me

/p\

Me

(%a)

(97)

S II ,F MCOP, X (9Xb)

(99)

The vibrational spectra of the fluorophosphorane (I 00) have been analysed and assignments have been made which are consistent with a trigonal-bipyramidal structure with a radial PhS g r 0 ~ p . l The ~ ~ nonequivalence of the axial fluorine atoms in the lBFn.m.r. spectrum may be due to the phenyl ring lying over one of the axial fluorine atoms. The spectrum of PhAsCI, is also consistent with a trigonal-bipyramidal structure with a radial phenyl group.*43See also studies on the trichloromethylphosphorane (10f).144A new theoretical approach has been made, aimed ly8

lag

140 141 Ira 143

J. P. Majoral and J. Navech, Bid/. Sac. chitti. France, 1971, 1331; J. P. Majornl and J. Navech, ibid., 1971, 95; J. P. Majoral, R. Kraemer, J. Devillers, and J. Navech, ibid., 1970, 3917. 0. A. Raevskii, R. R. Shagidullin, I. D. Rorozova, L. E. Petrova, and F. G. Khalitov, Izuest. Akad. Natrk S.S.S.R., Ser. kliim., 1970, 1725. H. P. Nguyen, N. T. Thuong, and P. Chabrier, Compt. rend., 1970, 271, C , 1465. J . R. Durig and J. W. Clark, J . Chem. Phys., 1969, 50, 107. A. H. Norbury, S. C. Peake, and R . Schmutzler, Specfrachim. Acta, 1971, 27A, 151. D. M . Revitt and D. B. Sowerby, Spectrochitii. Acfn, 1970, 26A, 1581. R . R. Holmes and M . Fild, J . C/ieni. P h y s . , 1970, 53, 4161.

Physical Methods

273

at identifying the manner in which processes like pseudorotation occur (see Section 4 of this Chapter). The vc-o bands appear as doublets in the spectra of metal carbonyl phosphite complexes. The intensities of the two peaks vary with temperature and they are therefore attributed to conformational differences within the P(OR), 1igar1d.l~~ 1 .-

C . Studies of Bonding.-Force constants have been determined for a wide range of thiophosphates (102).146 The force constants are lowered for all the bonds to phosphorus when oxygen is replaced by sulphur or when chlorine is replaced by sulphur. When the methoxy-group is replaced by M ~ fp(.l ) decrease whilst fpo and fps increase. Here the chlorine, ~ I ’ o ~ and influence of the decreased electronegativity is compensated by the change from a First to a Second Period element. A set of Urey-Bradley force constants were refined from the vibrational frequencies of OPHal,, Me,PO, etc. and used to calculate the spectra of other related molecules such as OPFClBr.147 The force constants and bond orders for the oxides (103, M = N, P, or As) have been compared. The force constant and bond order for the P - 0 group were easily the largest amongst the three compounds - a result which may be rationalized in terms of d,-p, bonding.14* An extremely interesting theoretical study on d,,-p, bonding in the PO group indicates that non-bonded interactions, which act to stretch bonds, tend to increase as the .rr-bonding order decreases, i.e. n-bonding also decreases non-bonded interactions.14u This study, like several other similar studies involving d-orbitals, suggests that the most important effect of including d-orbitals in the calculation is to alter the electron distributions. (See also Section 7 of this chapter.) The total 3d population indicated by the EHMO study was entirely comparable to that obtained from the valence-bond model; however, the usage of the various d-orbitals was different. The i.r. and Raman spectra of the cyclic phosphate (104) and its SbCI, complex have been assigned and force constants and bond orders calculated.160 The high frequency of vp-0 (1308 cm-l) may be due to a strong 145

140

14’

lo8 Id@ 150

D. A. Brown, H. J. Lyons, and A. R. Manning, Inorg. Chim. Actn, 1970, 4, 428. 0. A. Wafa, A. Lentz, and J. Goubeau, Z. niiorg. Chem., 1970, 378, 273; 0. A. Wafa, A. Lentz, and J. Goubeau, ibid., 1971,380,128; V. Hornung, 0. A. WaFd, A. Lentz, and J. Goubeau, ibid., 1971, 380, 137. S. T. King and R. A . Nyquist, Specfrochitn. Actn, 1970, 26A, 1481. F. Choplin and G. Kaufmann, Spectrochitn. A c f a , 1970, 26A, 21 13. L. S. Bartell, K. S. Su, and H. Yow, Inorg. Chpiti., 1970, 9, 1903. J. Hildbrand and G. Kaufmann, Spectrochitn. Acto, 1970, 26A, 1407.

274

Orgnrrophosphor~usChemistry 0

(107)

( 104)

n-bonding contribution. A similar explanation was advanced to explain the high shielding of the phosphorus atom in the corresponding phosphite. It will be interesting to study the relationship between v p = o and 8p and to compare the results with those for the phosphites (see Table 2). In this regard, calculations based on the so-called ‘energy-rich’ pyrophosphate bonds suggested that the 3d-orbitals of phosphorus are able to contribute more to the m-bond strengths of the terminal P - 0 bonds.Is1 A correlation between vp=o and Sp would not be expected when the electronegativity of the P-substituents alters.13 Correlations are observed when the structural changes are well removed from the phosphorus atom, e.g. Sp and vPNctfor the phosphazenes (13).16 The bands at 1600 and 1490 cm- are strong and weak respectively for arylarsonium salts, with the intensities reversed for the a r ~ i n e .The ~ ~ ratio ~ for aromatic amine salts is the same as for the arsine. This could reflect the absence of conjugation in the amine salts and in the arsine but the presence of conjugation in the amine and in the arsonium salts. The possibility of both pn-p,, conjugation and d,,-p,, conjugation in phosphines with aromatic, vinylic, and other m-bonded groups has led to some interesting work aimed at differentiating the two effects. When the phosphorus substituent is a nitrile group it would be surprising if p,,-p,, conjugation did not occur. Thus the higher magnitude of f l > - ~ (and ~) lower f C - for ~ the phosphine (105) compared with the corresponding oxide and sulphide is best rationalized in this way.153 However, the similar effects observed for the triacetylenic phosphines (106) (i.e. increase in fpc and decrease in f,-cl compared with non-conjugated models) could equally be due to d,,-p,, In fact, deshielding of the acetylenic proton observed in the lH n.m.r. spectrum suggests this may be the case. However, this is countered by the crystal structure, which shows that the PCCX atoms are not linear (see Section 7). Comparison of calculated i.r. frequencies for linear and non-linear PCCX molecules with those observed was not h e 1 p f ~ l . lA ~ ~comparison of solid and solution spectra might help ascertain the relevance of the X-ray work. In the A2-phospholens, conjugation is assisted by the cyclic nature of the system and vc-c is lower than in the corresponding As-phospholens. The ’H and 31Pn.m.r. spectra supported a + A4 effect rather than a - A4 effect (d,,-p,, conj~gation).~* 31 IK9 163

IG4

D . B. Boyd, Theor. Chim. Acra, 1970, 18, 184. M. A. A. Beg and Samiuzzaman, Pakistan J . Sci. Ind. Res., 1970, 12, 330. W. Koch, €3. Blaich, and J. Goubeau, Reu. Chim tninPraIe, 1970, 7 , 1 1 13. W. M. A. Smit and G. Dijkstra, J . Mol. Structure, 1971, 7 , 223.

Physicnl M Pt hods

275

The hydrogen-bonding ability of triethylphosphine with pyrrole, [see (107)], and phenol has been studied in hexane solution by i.r. spectroscopy and compared with that of other electron Equilibrium constants were estimated from the relative intensities of free and hydrogen-bonded N H or OH. The equilibrium constants with pyrrole were 1.53 (Bu,P), 0.89 (Et,P), and 0.37 (Et,As). There was a significant decrease as the temperature was raised. The better hydrogen-bonding ability of tri butylphosphine must be due to increased inductive donation to phosphorus since it cannot be due to solvation effects in hexane solution. Although the s-character of the electron lone pair on I?'" atoms is believed to be very high, this work shows that they have sufficient p - or &orbital character to give the lone pair the directional properties required for the hydrogen bonding. A wider range of electron-pair donors was studied, with phenol as the hydrogen donor 156 [see (108)]. It was found that the decrease in absorptivity of the O H band, as the atomic weight of M increases, is at a maximum for Group V and at a minimum for Group VII elements, which parallels the change in s-character of the lone electron pair in each Group.

( 107)

(108)

The force constants of the Ni-P bond in Prrnickel carbonyl complexes increase in the order Me,P < PH, < P(OMe), < PF3.15' This order is different from that of the donor-acceptor character, as estimated from ~ ( - 0 . The lengthening of the P - 0 bond of triphenylphosphine oxide upon complexation with uranium oxide has been estimated by i.r. However, X-ray diffraction shows little difference in the P-0 bond lengths (see Section 7). Some SCF-MO calculations on the donor-acceptor properties of Me,PO and H,PO have been ~ e p 0 r t e d . l ~ ~ 4 Microwave Spectroscopy

EHMO calculations on the phosphiran (109) are relevant to microwave studies of compounds in this series.'~lo The calculations suggest that inversion involves all the atoms of the ring, including the hydrogens, and that although the 3d-orbitals of phosphorus do not participate very much IG5 loo lb7

Ion

J . Chojnowski, Bull. Acad. polon. Sci., Sdr. Sci. chim., 1970, 18, 309. J. Chojnowski, Bull. Acad. polon. Sci., SPr. Sci. chit)]., 1970, 18, 317. M. Bigorgne, A. Loutellier, and M. Pankowski, J . Organometallic Chent., 1970, 23, 201. G. Bandoli, G. Bortolozzo, D. A. Clemente, U. Croatto, and C. Panattoni, Inorg. Nuclear Cheni. Lerrers, 1971, 7 , 401. I. H.Hillier and V. R. Saunders, J . Cheni. Sou, ( A ) , 1970, 2475.

276

Organophosphorus Cheniistry

in the filled molecular orbitals, their presence does alter the charge distribufion.lso There appears to be considerably less localization of the lone electron pair on phosphorus compared to nitrogen in aziridine and nearly 90% of this is in the p z orbital. The equilibrium comformations of cyclopropylphosphine (1 10) and its deuteriated analogues have been estimated from their microwave spectra.lG1 The P-C bond length (183.4 pm) is shorter than that of dimethylphosphine ( I 84.8 pm), in accordance with the presence of conjugation between the phosphorus atom and the cyclopropyl ring. It would be interesting to establish the type of conjugation which is involved. EHMO calculations on (1 11) indicate the presence of an in-plane interaction between the Walsh orbitals of the cyclopropyl ring and the phosphorus 3d-orbitals ( 3 4 , and 3dZz).lG2 H

H H , m H P €4,

A model which takes into account the spin-rotation interaction has been found to satisfactorily explain the v21 +- 0 rotation band of PH2.1s3 The millimetre-wave spectra of HCP and DCP have been compared with those of HCN and DCN.le4 A method of estimating frequencies of bands in this region due to processes such as pseudorotation has been suggested. This new approach involves calculation of the rovi bronic energy levels from the effects of quantum-mechanical Microwave spectra obtained from PH2D and PHDz in a magnetic field of about 25 kG showed Zeeman effects, from which molecular g values were calculated.166 They were 20 times smaller than those for ammonia. The molecular quadrupole moments of phosphine and ammonia were approximately the same. Magnetic susceptibilities and molecular quadrupole moments were also compared. 5 Electronic Spectroscopy The U.V. maximum at 330nm obtained after flash photolysis of tetraphenyldiphosphine has been attributed to the Ph2P' radical.lB7 The spectrum of the benzophosphole system (65), like that of methylphosphole, resembles the spectrum of the corresponding pyrrole analogue.Q1 The H. Petersen and R. L. Brisotti, J . Amer. Chern. SOC.,1971, 93, 346. L. A. Dinsmore, C. 0. Britt, and J. E. Boggs, J . Chem. Phys., 1971, 54, 915. la2 D. B. Boyd and R. Hoffmann, J . Amer. Chem. SOC.,1971, 93, 1064. leS J. M. Berthou and B. Pascat, Compt. rend., 1970, 271, C, 799. J. W. C . Johns, J. M . R. Stone, and G. Winnewisser, J . Mol. Spectroscopy, 1971, 38, 437. 165 B. J. Dalton, J . Chem. Phys., 1971, 54, 4745. l E e S. G. Kukolich and W. H. Flygare, Chem. Phys. Letters, 1970, 7 , 43. I e 7 S. K. Wong, W. Sytnyk, and J. K. S. Wan, Cunud. J . Chem., 1971,49,994.

leD

la1

Physical Methods

277

conclusion that a phosphino-group acts as an electron donor when conjugated through a phenyl group to an acceptor group, but that it acts as an electron acceptor when opposed to a mesomerically donating group [see (1 12)] has been based on dipole, n.m.r., i.r., and U.V. spectroscopic evidence.2 Part of the latter evidence involving the optical excited state has been questioned because the opposing substituents have dominant effects on the spectra.lss When the opposing group is kept constant, e.g. Me,N, it is asserted that variation of the P-substituent does not indicate an interaction with the phosphino-group. In reply, the theoretical aspects of interpreting the spectra have been challenged,1ss in particular the assignment of bands using the one-electron-transition approach.

( 1 12)

Electronic spectroscopy, in combination with other physical evidence, has also been used to study PIv conjugation. There is agreement that the phosphorus atoms in phosphine sulphides (10) l2 and the phosphinimines (1 13) 170 act as electron acceptors. There is a corresponding enhancement of the U.V. absorption with increase in the donor properties of the opposing group Y. HMO calculations have been used to estimate the extent and type of d,,-p, conjugation inv01ved.l~~Although U.V. spectroscopy has problems of band assignment and the fact that it involves excited states, it is an attractive area of spectroscopy to which to apply MO calculations. For example, see work on (114).172 The spectra of sulphonyl phosphinimines (1 15) have also been examined.173a

Y&NX

R

R

0 1 \

P=NJJ

( 1 13)

I A r --P =N: S0,Ar

RI

(1 15) (1 14)

The spectra of stabilized methylenetriphenylphosphoranesindicate that the Ph,P= C- C= 0 and Ph3P=C- C= C- C= 0 chromophores give maxima in the regions 275-305 and 350-400 nm, respectively.s1 The G. P. Schiemenz, 7etrahedron Lefters, 1970, 4309. H. Goetz, Tetrahedron Lerrers, 1971, 1499. H. Goetz, B. Klabuhn and H. Juds, Annulen, 1970, 735, 88. H. Goetz and F. Marschner, Tetrahedron 1971, 27, 1669. H. Goetz, B. Klabuhn, and H. Juds, Annulen, 1970, 735, 88. M. I. Shevchuk, A. F. l f J a H. Goetz and J. Schmidt, Tetrahedron Letters, 1971, 2089; Tolochko, and A. V. Dombrovskii, Zhur. obshchei. Khim., 1971, 41, 540. IG9

10

278


effect of changing the structure of the group R in compounds of the type ( 1 16) is r e ~ 0 r t e d . l ' ~The ~ pH dependence of the spectra of phosphine~ ~ bonding quinone adducts ( 1 17) has been used to aid i n t e r ~ r e t a t i 0 n . l The of nucleotides to enzymes has also been studied using U.V.

?Ph,P=C

I

,CH2C, H,N O2 'COR

R QPR3 OH

( 1 16)

The simultaneous analysis of orthophosphate, glycerol phosphates, and inositol phosphates has been achieved by spectrophotometric analysis of the molybdovanadate complexes.17s Also, a sensitive and selective chemiluminescent molecular emission method for the estimation of phosphorus and sulphur is described,177which is based on passing solutions into a cool, reducing, nitrogen-hydrogen diffusion flame. For organic compounds it was usually necessary to prepare test solutions by an oxygen-flask combustion technique. 6 Rotation and Refraction The racemization of the phosphine (118) has been followed by optical rotation. The lack of a solvent effect indicates that there is little change in Circular dipole moment in the formation of the planar transition dichroism has been used to study the interactions of nucleotides with proteins170 and DNA with a histone.l*O Faraday effects have been reviewed.lal Refraction studies on chloro-amino-phosphines,la2fluoroand some chalcogenides lS4 are reported. PI,'

..P.

\-w Me

( 1 18) M. A. A. Beg and M. S. Siddiqui, Reu. Roumaitie Chim., 1970, 15, 1653; M. A. A. Beg and M. S. Siddiqui, Pukistan J. Sci. Ind. Res., 1970, 12, 334. 175 C. Roustan, L. A. Pradel, R. Kassub, A. Fattoum, and N. V. Thoai, Biochim. Biophys. Acta, 1970, 206, 369. 176 E. M. Bartlett and D. H. Lewis, Analyt. Biochetn., 1970, 36, 159. 17' K. M. Aldous, R. M. Dagnall, and T. S. West, Analyst, 1970, 95, 417. 178 H. D. Munro and L. Homer, Tetrahedron, 1970, 26, 4621. 1 7 @ K. Wulff, H. Wolf, and K. G. Wagner, Biochern. Biophys. Res. Cotntn., 1970, 39, 870. l a 0 T. E. Wagner, Nature, 1970, 227, 65. D. Voigt, M. C. Labarre, and J. F. Labarre, Colloq. Znt. Cent. Nar. Rech. Sci., 1970, 17(

115.

S . Senges, M. Zentil, and M. C. Labarre, Bull. Soc. chim. France, 1971, 351. M. Zentil, S. Senges, J. P. Fancher, and M. C. Labarre, Bull. Soc. chim. France, 1971, 376. lY4 V. Baliah, C. Srinivasan, and M. M. Abubucmer, Indian J. Appl. C'hern., 1970, 8, 981.

279

Physical Methods

7 Diffraction Although the aminodifluorophosphine (1 19) is planar about the nitrogen atom in the c r y ~ t a l electron ,~ diffraction shows that in the gaseous phase the molecules are slightly pyramidal, the angle between the RNR plane and the N-P bond being 32" for (1 19, R = Me), 35" for (1 19, R = H).la5 The P-N bond (168 and 166 pm long, respectively) is longer, but the P-F bond (158-9 pm) is shorter than in the crystal. Whereas these P-N compounds appear to possess a staggered conformation, electron diffraction studies on tetramethyldiphosphine indicate that it deviates by 16" [see (120)] from the staggered conformation.la6 This may be due to a shrinkage effect involving low torsional frequency oscillation about the P-P bond, which would also explain the slight non-equivalence of the methyl groups in the n.m.r. spectrum. With the interest in estimating the relative importance of pn-p,, and d,,-p,, conjugation in P'" compounds, it is of significance that the P--C=C-Y group in (106, Y = H) deviates from linearity by about 10" in the c r y ~ t a 1 . lThis ~ ~ cannot be explained by d,,-p,, conjugation and parallels a similar deviation for P(CN)3. An electron diffraction study on the monoacetylenic and mononitrile compounds should be very rewarding. 61.

Me

(120)

The crystal structures of a number of diphosphine disulphides ( 1 21) and (122) show a remarkable constancy in the bond Iengths.laa Two types of molecule are observed in the crystal of the tetramethyl compound (1 21, X = Y = Me).ls9 The crystal structure of triphenylphosphine oxide (P-C 176pm, P - 0 164pm) varies little from that observed in the uranium oxide complexes,1goand does not confirm P-0 bond lengthening in complexes, as indicated by vp-0 (see Section 3C).

(121) IR6

lg0

(1 22)

G . C. Holywell, D. W. H. Rankin, B. Beagley, and J. M. Freeman, J . Cheiti. SOC.( A ) , 1971, 785. A. McAdam, B. Beagley, and T. G . Hewitt, Trans. Faraday SOC.,1970, 66, 2732. J. Kroon, J. B. Hulscher, and A. F. Peerdeman, J . Mol. Structure, 1971, 7,217. J. D.Lee, J . Inorg. Nuclear Chem., 1970, 32, 3209. J . D.Lee and G. W. Goodacre, Acta Cryst., 1971, B27, 302. G. Bandoli, G . Bortolozzo, D. A . Clemente, U . Croatto, and C. Panattoni, J . Cheijr. SOC.( A ) , 1970, 2778.


280

The phosphinimine (123) has a 156.7 pm P-N bond length and 124.2" PNC bond angle,lgl which indicates a large P-N double-bond character. The angle is much larger (137") in the phosphinimine (124), probably due to steric crowding. However, the P-N bond is shorter (153 pm) in (124), which may mean that the sterically induced increase in PNC angle permits additional .rr-bonding - possibly d,-p, bonding. The P-N bond is shorter still (146.9 pm) when the phosphorus atom bears a fluorine atom and the nitrogen atom bears an electron-donating methyl group,1g2as in (125); however, the PNC bond angle (1 19O) shows no evidence of widening due to d,,-pn bonding. Br

0 02yJ02 Me

Ph,P=N

(1 23)

Ph,P=N

'

Ph,FP=N

N PPh,

/

( 125)

NO2 ( 1 24)

The crystal structure of the cyclopentenylidenephosphorane ( 1 26) shows significant shortening of the bonds 'a' and 'b' and the 'b' ester group is co-planar with the central ring.lg3 This is in accordance with a strong conjugative interaction. This conformation is probably also dominant in solution (see Section 1 D). There was no evidence of shortening of the P+-0- distance by electrostatic attraction. X-Ray data on the minor isomer of the phosphetan oxide (1 27) show that it has a bent conformation, with the P-phenyl and C(3)-methyl groups as far apart as possible.194 Electron diffraction has shown a large difference in stereochemistry between A2-phospholens and A3-phospholens. The ring is planar in the A2-phospholen (128)Ig5with a CPC bond angle of ca. 94.2" whereas the As-phospholen (129)loShas an envelope shape with a CPC bond angle of ca. 98.5". A large difference in physical properties would not be surprising for they differ in stereochemistry, conjugation, and (since the CPC bond angles are different) in hybridization too. X-Ray diffraction has shown that the phosphole (130) has ring angles which are similar to those of thiophen.lo7 Evidence has been presented which shows that this molecule has aromatic character similar to that of pyrrole, yet unlike pyrrole derivatives the hetero-substituent is not in the plane of the ring. This is believed to be associated with the different barriers to inversion. lQ1 loa

lQ3 la4

Io8

lg7

M. J. E. Hewlins, J . Chem. SOC.(B), 1971, 942. G. W. Adamson and J. C. J. Bart, J . Chem. SOC.( A ) , 1970, 1452. 0. Kennard, W. D. S. Motherwell, and J. C. Coppola, J . Chem. SOC.( C ) , 1971, 2461. Mazhar-ul-Haque, J . Chem. SOC.( B ) , 1971, 117. V, A. Naumov and V. N. Semashko, Doklady Akad. Nauk S.S.S.R., 1970, 193, 348. V. A. Naumov and V. N. Semashko, J . Struct. Chem., 1970, 11,919. P. Coggon, J. F. Engel, A. T. McPhail, and L. D. Quin, J . Amer. Chem. Soc., 1970, 92, 5779.

Physical Methods

28 1

c=o

/

Me0

Me0 ( 126)

Me

Ph

Like other derivatives, the PIv phosphorin (131) has an almost planar ring in the crystal. The NPN bond angle (101.6') is larger than that of the corresponding dimethoxy-compound, probably because of spatial dernands.lB8 A very interesting comparison of the electronic structures of the PIr and PI" phosphorins and pyridine has been carried out by means of CNDO The results indicate that (a) unlike the nitrogen atom in pyridine the P" and PIv atoms donate cr charge to the ring, (6) the phosphorus atom withdraws about the same amount of 7~ charge as nitrogen but takes it from the /%carbon atoms, not the a and y atoms. The different charge distribution produced by the participation of d-orbitals has been found before, but this present example serves to show the dramatic effect that can be produced.

Yh

Ph

APh

Mc,N

lgU lpB

:p\

NMe,

U . Thewalt, C. E. Bugg, and A. Hettche, Attgew. Chem. Internat. Edn., 1970, 9, 898. H. Oehling and A. Schweig, Tetrahedron Letters, 1970, 4941.

282

Orgaiiophosphoriis Chemistry

An X-ray diffraction study on the phosphorinone (132) showed that it has a chair conformation which is slightly flattened about the phosphorus atom compared with cyclohexanone.200 Also, the P-phenyl group is tilted outwards away from an axial position. If the compound favoured a conformation with a truly axial phenyl group as shown in (133), J l > ( l f f A and J P C Hwould ~ be expected to be the same since the two protons would be equidistant from the lone electron pair on phosphorus. The observation of different constants at first suggested that the molecule preferred a conformation with an equatorial phenyl group, but it is now clear that a conformation similar to that in the crystal would also possess different coupling constants, and must now take preference as the most likely conformation in solution. The structure of dimethyl 1-hydroxycyclododecylphosphonate is also reported.201

Tn the triethylammonium salt of uridine-2’,3’-00-cyclophosphatothioate the bond lengths to the terminal oxygen and sulphur atoms of the phosphate group (PO 148 pm; PS 194.6 pm) indicate that there is no delocalization of charge on to the sulphur atom,202and the cation is situated close to the oxygen atom. Crystals of sodium cytidine-2’,3’-phosphate contain two types of molecule; one has a planar ribose ring whereas in the other molecule the ring is puckered.203 It is found that the tetra-isoamylphosphonium cation does not take a roughly spherical shape but accommodates an iodide ion 480 pm from the phosphorus atom.204 Neutron diffraction of phosphonium bromide crystals shows no evidence of h y d r o g e n - b ~ n d i n g . The ~ ~ ~ structures of bis(trimethy1phosphine)silicon tetrachloride 206 and the iridium salt (1 34)207 are also reported.

201 202

203 204

2os

207

A. T. McPhail, J. J. Breen, and L. D. Quin, J . Amer. Chem. SOC., 1971, 93, 2574. G. Samuel and R. Weiss, Tetrahedron, 1970, 26, 3951. W. Saenger and F. Eckstein, J . Amer. Chern. SOC.,1970, 92, 4712. C. L. Coulter and M. L. Greaves, Science, 1970, 169, 1097. U . P. Krasan, U. P. Egorov, and N. G. Feshchenko, J . Struct. Chem., 1970, 11, 879. L. W. Schroeder and J. J. Rush, J . Chem. Phys., 1971, 54, 1968. H. E. Blayden and M. Webster, Inorg. Nuclear Chem. Letters, 1970, 6, 703. J. M. Guss and R. Mason, Chem. Comm., 1971, 58.

283

8 DipoIe Moments, Polarography, and Other Electrical Properties The dipole moment of tributylphosphine varies from 1.49 to 2.4 D according to the solvent used.2o8 Inductive effects in phosphines have been estimated by comparing the calculated and observed dipole moments,209and the apparent dipole moment due to the lone electron pair on phosphorus has been estimated.210 A method of calculating the hybridization of the phosphorus atom in terms of bond angles is suggested which leads to a linear relationship between hybridization ratio and lone electron pair The difference between experimental and calculated dipole moments for para-substitued arylphosphines,2 phosphine sulphides,12 and phosphinimines 170 has been used to estimate mesomeric transfer of electrons to phosphorus. The Debye method of calculating dipole moments is found to be unsuitable for strongly polar substances ( p above 3-5 D depending on its molar volume). Values of k 5% accuracy are claimed by using the Onsager formula and taking atomic polarization into account.211 Thus dipole moments of long-chain phosphine chalcogenides and phosphonium salts were 1 and 10 D higher (respectively) by the second method. Dielectric constants of these compounds decreased with increased concentration, presumably due to association in antiparallel form. The bond moments, P=Ch and Pfl-, were tabulated. The presence of d,-p, bonding between vinyl groups and phosphonic ester groups was confirmed by dipole moment studies.212 The presence of a strong dipolar group (a nitrile group) in the a-position (e.g. 135) appeared to strongly influence the relative stabilities of the conformers. Dipole moments for some related chloro-compounds have also been 208

Zo9

210

211 21a

213

J. P. Fayet, M. Pradayrol, and P. Mauret, Compc. rend., 1970, 271, C, 1033. 0.A. Raerskii and F. G. Khalitov, Itvest. Akad. Nauk S.S.S.R., Ser. khim., 1970, 2368. J. P. Fayet and P. Mauret, J . Chim. phys., 1971, 68, 156. Yu. Ya. Borovikov, E. V. Ryl'tsev, I. E. Boldeskul, N. G. Feshchenko, Yu. P. Makovetskii, and Yu P. Egorov, Zhur. obshchei Khim., 1970, 40, 1957. E. A. Ishmaeva, A. N. Vereshchagin, B. A. Bondarenko, G. E. Yastre'ova, and A. N. Pudovic, Izoest. Akad. Nauk S.S.S.R., Ser. khim., 1970, 2695. A. V. Dogadina, B. I. Ionin, K. S. Mingaleva, and A. A. Petrov, Zhur. obshchei Khim., 1970, 40, 2341.

284

Organophosphorus Chemistry 0 II ( E t 0 )%P -C =C HA r

I

CN (135)

Conformational populations of cyanomethylphosphine oxides (1 36) have been estimated from dipole moments and indicate a preference for the t r a n s - c o n f ~ r m a t i o n . The ~ ~ ~moments of the 0-,rn- and p-chloro- and tolylderivatives of triaryl phosphites (1 37, Y = :) and triaryl phosphates (1 37; Y = 0) indicate that the oxygen atom in the latter series causes the aryl rings to rotate further away from a position in which their planes all meet along the molecular symmetry axis.215 Conformational studies have also been carried out on the dioxaphosphorinanes.216 The moments of the isomeric series (138a) and (138b) were in the ranges 3 . 7 4 . 2 and 5.4-5.5 D respectively.75

Not surprisingly, the dipole moments of 1 : 1-complexes of phosphines and aluminium chloride are very large. Triethylphosphine also forms a 2 : I complex whose very low dipole moment suggests a symmetrical structure such as (1 39).36 Polarographic studies are reported on thioesters, mainly of the type (140) and (141),217 and on trichloroethylphosphonites.2** In the field of nucleotides and nucleosides it is found 219 that ATP has a very high surface activity at the mercury electrode, which is strongly dependent upon complex formation with transition metals, The polarographic behaviour of cobalt complexes with triphenylphosphine and its oxide 220 has been studied in order to estimate extraction efficiencies. Et,P I /Cl S S CI-AI II II I 'CI PEt,

(13%

( R10)2PR2

140)

(R10)?POR2

(141)

E. A. Ishmaeva, A. N. Pudovik, and A. N. Vershchagin, Izoest. Akad. Nauk S.S.S.R., Ser. khirrt., 1970, 2790. 216 C. W. N. Cumper and A. P. Thurston, J . Chem. SOC.( B ) , 1971,422. 21a B. A. Arbuzov and R. P. Arshinova, Doklndy Aknd. Nauk S.S.S.R., 1970, 195, 835. 217 G. S. Supin and V. V. Ivanchenko, Gigiena i Sanit., 1971, 36, 76. al* T. Giovanoli-Jukubczak, B. Fitak, and J. Chodkowski, Chem. analif., 1971, 16, 3 8 3 . "lo H. Sohr, K . Lohs, and G . Koenig, J . Electronnal~~t. Chem. Interfacial Electrocherii., 1970, 21, 421. l a o P. Broquet and M. Parthault, Conipf. rend., 1970, 270, C, 1798. 214

Physical Methods

285

Dielectric relaxation studies of phosphorylated polyethers from - 180" to 200 "C have been used to study their structures.221The magnitude of the dielectric constants of high-phosphonic-acid-contentpolymers is much larger than predicted, which suggests a microphase-separated structure. Conductance studies on some aryl- and alkyl-phosphonium salts showed a higher conductance for the halides than for the nitrate.222 9 Mass Spectrometry

1-Methylphosphorinone upon electron bombardment tended to undergo P-C and C-H bond cleavage rather than the C(2)-C(3) cleavage observed for the nitrogen analogue.223 A summary of the fragmentation is shown in Scheme 1. The transferance of oxygen from carbon to phos-

0

Q I

Me

+:$M -e

1

H

Mc,P -o+ Scheme 1

phorus may occur via a bridge species as shown. The ready formation of phosphinylium ion (142) and phosphonylium ion (143) (phosphacylium ions) has been observed for dialkylphosphinic This type of fragmentation is also very important for the cyclic aromatic phosphinic ester (144; R = H, Y = NH, Z = OMe) and for the oxides (144; R = H,

221

22s 224

P. J. Phillips, F. A. Emerson, and W. J. MacKnight, Macromolecules, 1970. 3, 771. A. Fidlcr and J. Vrestal, Coll. Czech. Chem. Comm., 1970, 35, 1905. L. D . Quin and T. B. Taube, J . Chem. SOC.( B ) , 1971, 832. P. Haake and P. S. Ossip, Tetrahedron, 1968, 24, 565.

286


Y = NH, Z = H or Et) (see Scheme 2).,,, The phosphinylium ion (145) then loses PO to give a dibenzopyrrolium ion (146; R = H, Y = NH). The corresponding sulphur-bridged ester (144; R = Me, Y = S, Z = OR) has a similar fragmentation pathway.22s Since sulphur is more easily expelled than NH, the ion (147) is also observed. In the acid (144; R = Me, Y = S, Z = OH) the phosphinylium ion is by-passed and loss of P 0 2 H gives (146, Y = S) directly. The acid also has a strong tendency to

a:n

R

P

R

R

Scheme 2

lose SH, presumably after protonation of sulphur by the acidic group. I n the sulphones (144; R = Me, Y = SO2, Z = Me) there is once again a strong tendency to give the phosphinylium ion (145; R = Me, Y = SO,). The phosphine oxide (144; R = Me, Y = SO2, Z = Ph) also shows loss of PhO to give (148; R = Me) possibly via the phosphinite, and the phosphines (149) fragment with loss of ArPH.

228

R, A. Earley and M. J, Gallagher, Org. Mass Spectrometry, 1970, 3, 1287. I. Granoth, A. Kalir, Z . Pelah, and E. D. Bergmann, Org. Mass Spectrometry, 1970, 3, 1359.

Physical Methods

287

The mass spectra of some t-butylphosphinic acids, e.g. (150), are extremely The t-butyl groups fragment in two ways, either by elimination of a methyl group or by elimination of isobutylene. The latter process is only observed when a P-t-butyl group is present whereas loss of a methyl group, although relatively slow for a P-t-butyl group, is important when the t-butyl group is bound to a phenyl group. Work on stabilized alkylidenephosphoranes of the type (1 51) shows 22* that the usual cyclization across the ortho-positions of two of the P-phenyl groups to give (152) may be followed by phenyl migration and PC cleavage to give (153), a strongly stabilized carbonium ion. As steric crowding around the PPh3 moiety increases, so the intensity of the Ph3P+ion increases to bcconie the base peak at the expense of the molecular ion and M - 1 ion [Ox for (154)]. The presence of an electron-withdrawing group on the fluorene grouping has the opposite effect. The mass spectrum of N-phenyltriphenylphosphinimine (1 55) has been the main feature being the resistance of its molecular ion to fragmentation.

\

/

p/Pll

I’ll (153)

CyD (151)

( I 5’)

Most of the ions in the spectrum of isothiocyanate derivatives of cyclophosphazenes are cyclic.23o The CNS group fragments to give abundant ions M - S, M - S2,and M - CS,. A great deal of interest has been shown in the mass spectral analysis of natural products. In most cases it is desirable to develop techniques incorporating g.1.c. to enable the separation of the components obtained in extracts from natural products. The volatility required for g.1.c. is la’

la*

230

R. Brooks and C. A. Bunton, J . Org. Chem., 1970, 35, 2642. E. D. Bergmann, M. Rubinovitz, C. Lifshitz, D. Shapiro, and I. Agranat, Org. Muss Spectrometry, 1970, 4, 89. L. Tokes and S. C. K. Wong, Org. Muss Spectrometry, 1970, 4 (suppl.), 59. A. J. Wagner and T. Moeller, J. Chern. SOC.( A ) , 1971, 596.

28%


frequently achieved by making trimethylsilyl (TMS) derivatives of the hydroxylic functions. In the phosphoryl-ethylamines and ethanolamines the POH and NH functional groups are silylated to give (156) and (157).231 0

0

II

II

( T M SO)2 P -0-C H, C H2N( T hl S )

( TMS0)2PCH,CH2N(ThIS),

( 156)

( 1 57)

OH I HOCH,.CHOH*CH,OP-Y II 0 (1 58)

The base peak is due to (M - TMS)+ and ions arising from cleavage of the CC and PC or PO bonds are also common. The glycerophospholipids tend to undergo pyrolysis on g . 1 The ~ ~spectra ~ ~ of TMS derivatives of (158, Y = OH, glycerol, ethanolamine, serine, or inositol) possess a very low abundance of molecular ions. However, peaks at (M - Me)+, (M - TMS)+, (A4- TMSOH)+, and (A4 - TMSOCH,)+ serve to identify the molecular The fragmentation of the /?-isomer of the glycerophosphate is sufficiently different from that of the a-isomer to enable their differentiation. In work towards a method of obtaining sequence information, a number of volatilizing derivatives of the furanose system have been examined, e.g. TMS, acyl, trifluoroacetyl, acetonyl, and boronyl The latter, combined with TMS derivatization, was found to be the most suitable for determining the type of base at the 3' position. The spectra of trimethylsilyl derivatives of the nucleotides RNA, DNA, AMP, etc., and derivatives deuteriated in the TMS group showed that phosphate-bound TMS groups were the most resistant to cleavage.236 Nu9eotides with a total of four TMS groups gave P(OTMS), and HOP(OTMS)s ions. Major ions consisted of the intact base plus certain portions of the sugar skeleton and of fragments derived from the phosphate ester. Atomization energies of CP, C2P, CP2, and CzPz have been determined using high-temperature Knudsen cell mass spectrometry.2S6 10 pK and Thermochemical Studies

The energies of protonation of the complete series of methyl and ethyl phosphines have been calculated.' pKa values for the hydroxyphenylK. A. Karlsson, Biochem. Biophys. Res. Comm., 1970, 39, 847. M. G. Horning, G. Casparrini, and E. C. Horning, J. Chromatog. Sci., 1969, 7 , 267. J. H. Duncan, W. J. Lennarz, and C. C. Fenselau, Biochemistry, 1971, 10, 927. 23d J. J. Dolhun and T. L. Wiebers, Org. Mass Spectrometry, 1970, 3, 669. a s s A. M. Lawson, R. N. Stillwell, M. M. Tacker, K. Tzuboyama, and J. A. McCloskey, f. Amer. G e m . Soc., 1971, 93, 1014. IY6 S. Smoes, C. E. Myers, and J. Drowart, Chem. Phys. Letters, 1971, 8, 10.

231 132

289

Physical Methods

phosphines (159; Y = :) and phosphine chalcogenides (159; Y = 0 or S ) have been used to estimate Hammett constants.237 The results show that the phosphonyl group enters into direct polar electron-acceptor conjugation.

The acid strengths of a series of phosphonic acid derivatives in a variety of solvents have also been used to estimate Hammett constants.2R8In contrast to carboxylic acids, the phosphonic acids are stronger in ketonic solvents than in hydroxylic solvents, which may be attributed to the dissociation of phosphonic acids without the necessity to disrupt the dimeric nature of the acid (see Scheme 3).

B

’I--O \ C-K 4 ‘0-ll 0

I

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