Organophosphorus Chemistry Volume 32
A Specialist Periodical Report
Organophosphorus Chemistry
Volume 32
A Review ...
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Organophosphorus Chemistry Volume 32
A Specialist Periodical Report
Organophosphorus Chemistry
Volume 32
A Review of the Literature Published between July 1999 and June 2000 Senior Reporters D.W. Allen, Sheffield Hallam University, Sheffield, UK J.C. Tebby, Staffordshire University, Stoke-on-Trent, UK Reporters N. Bricklebank, Sheffield HaIlam University, Sheffield, UK C.D. Hall, King's College, London, UK M. Migaud, The Queen's University of Belfast, UK J.C. van de Grampel, University of Groningen, The Netherlands
RSC ROYAL SOCIETY OF CHEMISTRY
ISBN 0-85404-334-9 ISSN 0306-0713
0The Royal Society of Chemistry 2002 All rights reserved Apart from any fair dealing for the purposes of research or private study, or criticism or review as permitted under the terms of the UK Copyright, Designs and Patents Act, 1988, this publication may not be reproduced, stored or transmitted, in any form or by any means, without the prior permission in writing of The Royal Society of Chemistry, or in the case of reprographic reproduction only in accordance with the terms of the licences issued by the Copyright Licensing Agency in the UK, or in accordance with the terms of the licences issued by the appropriate Reproduction Rights Organization outside the UK. Enquiries concerning reproduction outside the terms stated here should be sent to The Royal Society of Chemistry at the address printed on this page. Published by The Royal Society of Chemistry, Thomas Graham House, Science Park, Milton Road, Cambridge CB4 OWF, UK Registered Charity Number 207890 For further information see our web site at www.rsc.org
Typeset by Computape (Pickering) Ltd, Pickering, North Yorkshire, UK Printed by Athenaeum Press Ltd, Gateshead, Tyne and Wear, UK
Introduction
The literature relating to the chemistry of organophosphorus compounds continues to grow. Our problem as Senior Reporters is to find authors who are willing to undertake the task of reviewing the various areas in a timely manner. The past year has been particularly difficult in this respect, and this volume lacks coverage of some areas that previously have been reviewed continuously over many years. Thus, this year, we are unable to provide a review of the chemistry of quinquevalent phosphorus acids, and the ‘Physical Methods’ chapter is also missing. The mononucleotide section of the normally extensive chapter on ‘Nucleotides and Nucleic Acids’ is provided by a new member of the team, Dr Marie Migaud (Queen’s, Belfast), but we have not been able to secure the usual coverage of polynucleotide and nucleic acid chemistry. On the credit side, we have a two-year review of the chemistry of tervalent phosphorus acid derivatives, making up for the absence of this topic in the previous Volume 31. We hope to remedy the deficiences of the present volume in a similar way next year. We would welcome approaches from potential authors, in particular for the ‘Physical Methods’ chapter, or specific sections thereof, as this topic requires an overview of the application of physical methods of all kinds across the whole of the organophosphorus area, and is a major undertaking. The synthesis of new chiral phosphines continues to be a major preoccupation, the main focus being applications in metal-catalysed processes. Interest in the synthesis and structural characterisation of metallo-organophosphide systems also continues to grow. In contrast, the volume of new work on lowcoordination number p,-bonded phosphorus compounds has declined, as the major features of this area have now become established, although much interesting new work continues to appear. The synthesis of new chiral ligand systems is also now a significant feature in the chemistry of tervalent phosphorus acid esters and amides, applications of such compounds in metalcatalysed processes hitherto having been neglected relative to those involving phosphine ligands. The past year has also seen continued interest in the structure of phosphonium ylides, with particular reference to gaining greater insight into their stability, electronic distributions and conformation, on which the reactivity of these systems depends. In the nucleotide field, the year has been marked by the development of new phosphorylation and chiral thiophosphorylation methods and by improvements in the formation of intramolecular pyrophosphate linkages. The year has seen yet another diminution in the number of publications dealing with hypervalent phosphorus chemistry but the quality of work V
vi
Introduction
remains high, relying heavily on the latest techniques in NMR spectroscopy and X-ray crystallography. Ample illustration of this is found in a study of cyclic phosphates, phosphonates and phosphonium salts containing sulfuryl groups. The work was designed to compare the coordinating ability of sulfur, reported earlier, with that of sulfuryl oxygen and in fact only one of a series of eight phosphates, phosphonates and phosphonium salts showed evidence of donor action towards phosphorus from phosphoryl oxygen, with a P-0 bond distance of 3.007 The keen interest in phosphazenes continues and many advances and further applications have been reported. There have been further studies of the azaWittig reaction, several of which focus on the synthesis of nitrogen heterocycles. Carbophosphazenes have been shown to ring-open tertiary bases, such as quinuclidine, to give amino-substituted derivatives. Several reports concern the preparation of ferrocenyl derivatives and much use has been made of silylated phosphazenes. Complexation with a wide range of metals has produced an interesting array of novel structures. Phosphazenes have been used as phase transfer catalysts and as strong bases, and crystals of a phenylenedioxide cyclotriphosphazene have been used to form inclusion compounds with various aromatics and polymers. Vinyl derivatives have been prepared, leading to fascinating dendritic architectures. A polyphosphazene derived from a chiral amine gave a large optical rotation assigned to the presence of a helical P = 3DN backbone. Applications as flame retardants abound and a polyphosphazene with pendant cyanate groups was cured to produce a novel cyclo-matrix with improved char yield. There has been much interest in polymers and copolymers, some being amphiphilic and capable of forming micelles. Platinum complexes with greater anticancer activity than Carboplatin have also been reported.
A.
D. W. Allen J. C. Tebby
Contents
Chapter 1
Phosphines and Phosphonium Salts By D. W.Allen
1
1 Phosphines 1.1 Preparation 1.1.1 From Halogenophosphines and Organometallic Reagents 1.1.2 Preparation of Phosphines from Metallated Phosphines 1.1.3 Preparation of Phosphines by Addition of P-H to Unsaturated Compounds 1.1.4 Preparation of Phosphines by Reduction 1.1.5 Miscellaneous Methods of Preparing Phosphines 1.2 Reactions of Phosphines 1.2.1 Nucleophilic Attack at Carbon 1.2.2 Nucleophilic Attack at Halogen 1.2.3 Nucleophilic Attack at Other Atoms 1.2.4 Miscellaneous Reactions of Phosphines
1 1
13 15 17 23 23 24 25 27
2 Phosphine Oxides 2.1 Preparation 2.2 Reactions 2.3 Structural and Physical Aspects 2.4 Phosphine Chalcogenides as Ligands
31 31 33 36 36
3 Phosphonium Salts 3.1 Preparation 3.2 Reactions
38 38 40
4 p,-Bonded Phosphorus Compounds
42
5 Phosphirenes, Phospholes and Phosphinines
47
6
53
References Chapter 2
1
Pentacoordinated and HexacoordinatedCompounds By C.D. Hall
74
1 Introduction
74
Organophosphorus Chemistry, Volume 32
0The Royal Society of Chemistry, 2002
vii
...
Contents
Vlll
2 Acyclic Phosphoranes
74
3 Monocyclic Phosphoranes
77
4 Bicyclic and Tricyclic Phosphoranes
79
5 Hexacoordinate Phosphorus Compounds
87
References Chapter 3
Tervalent Phosphorus Acid Derivatives By D. W.Allen
91
1 Introduction
91
2 Halogenopho sphines
91
3 Tervalent Phosphorus Esters 3.1 Phosphinites 3.2 Phosphonites 3.3 Phosphites
94 94 97 99
4 Tervalent Phosphorus Amides
Chapter 4
89
1.4 Aminophosphines 1.5 Phosphoramidites and Related Compounds
109 109 111
References
113
Nucleotides and Nucleic Acids By M. Migaud
120
1 Introduction
120
2 Mononucleotides 2.1 Nucleoside Acyclic Phosphates 2.1.1 Mononucleoside Phosphate Derivatives 2.1.2 Polynucleoside Monophosphate Derivatives 2.2 Nucleoside Pyrophosphates 2.2.1 Nucleoside Diphosphate Analogues 2.2.2 Nucleoside Diphosphosugars 2.2.3 Nucleoside Cyclic Pyrophosphates 2.2.4 Nucleoside Pyrophosphonates
120 120 120 133 139 139 139 140 141
3 Nucleoside Polyphosphates
141
References
153
ix
Contents Chapter 5
Ylides and Related Species By N. Bricklebank
157
1 Introduction
157
2 Phosphonium Ylides 2.1 Theoretical, Structural and Mechanistic Studies of Phosphorus Ylides and the Wittig Reaction 2.2 Synthesis and Characterisation of Phosphonium Ylides 2.3 Ylides Coordinated to Transition Metals 2.4 Reactions of Phosphonium Ylides 2.4.1 Reactions with Carbonyl Compounds 2.4.2 Miscellaneous Reactions 2.5 The Synthesis and Reactions of Aza-Wittig Reagents
157
3 Structure and Reactivity of Lithiated Phosphine Oxide Anions
180
4 Structure and Reactivity of Phosphonate Anions
180
References Chapter 6
Author Index
157 160 164 168 168 174 177
184
Phosphazenes By J. C. van de Grampel
188
1 Introduction
188
2 Linear Phosphazenes
188
3 Cyclophosphazenes
205
4 Polyphosphazenes
2 14
5
Crystal Structures of Phosphazenes and Related Compounds
222
References
23 1 24 1
Abbreviations
Benzamide adenine dinucleotide Cyclodiphospho D-glycerate Capillary electrophoresis Creatine kinase Controlled potential electrolysis 1-(2-chlorophenyl)-4-methoxylpiperidin-2-yl Cyclic voltammetry cv DETPA Di(2-ethylhexy1)thiophosphoric acid Dimethylacetylenedicarboxylate DMAD Dimethylformamide DMF DMPC Dimyristoylphosphatidylcholine DRAMA Dipolar restoration at the magic angle DSC Differential scanning calorimetry DTA Differential thermal analysis ERMS Energy resolved mass spectrometry ESI-MS Electrospray ionization mass spectrometry EXAFS Extended X-ray absorption fine structure FAB Fast atom bombardment 1-(2-fluorophenyl)-4-methoxylpiperidin-2-y1 FPmP High-performance liquid chromatography HPLC LA-FTICR Laser ablation Fourier Transform ion cyclotron resonance Matrix assisted laser desorption ionization MALDI Micellar electrokinetic chromatography MCE Mass-analysed ion kinetic energy MIKE Polycyclic aromatic hydrocarbons PAH Hydroquinone- 0,O’-diacetic acid QDA 9-[2-(phosphonomethoxy)ethyl]adenine PMEA S-acyl-2-thioethyl SATE Secondary ion mass spectrometry SIMS SSAT Spermidinelspermine-N1-acetyltransferase Static secondary ion mass spectrometry SSIMS TAD Thiazole-4-carboxamideadenine dinucleotide tert-Butyldimethylsilyl tBDMS Trifluoroacetic acid TFA Thermogravimetric analysis TGA Thin-layer chromatography TLC Time of flight TOF X-Ray absorption near edge spectroscopy XANES
BAD cDPG CE CK CPE CPmP
X
1
Phosphines and Phosphonium Salts BY D. W. ALLEN
1
Phosphines
1.1. Preparation. - 1.1.1. From Halogenophosphines and Organometallic Reagents. The use of organolithium reagents has once again dominated this approach in the past year, with few examples of the application of Grignard or other reagents being noted. An attempt to prepare the bulky triarylphosphine (1) from 2,4,6-tri(isopropyl)phenyllithium and phosphorus trichloride resulted in the formation of the P,P-diphosphine (2), which is unusually stable to further cleavage in the presence of the aryllithium reagent.' An improved route to ortho-substituted aryldichlorophosphines has been developed, enabling the synthesis of a wide range of new triarylphosphines (3).2 An improved route from o-dibromobenzene to the o-bromoarylphosphine (4) has enabled the ,pi
Pr'
Pr',
R
(3) R = SMe or OMe Ar = o-anisyl, p-CH3SC6H4, I-naphthyl or 9-anthtyl
(4)
synthesis of the o-dichlorophosphinoarylphosphine(9,from which a range of chiral o-phosphinoarylphosphite ligands has been ~ r e p a r e dA . ~wide variety of new phosphines has been described in the past year, the main focus being the synthesis of new ligands for application in metal-catalysed processes. Among simple ligands prepared by the above route are triarylphosphines bearing or tholpara-ether or thioether substituents, e.g. (6): the triarylphosphines (7), the bulky systems (S)6 and (9),7 and sterically-crowdedhomochiral ligands, e.g. (lo).' Phosphines bearing fluorinated substituents have attracted some interest, e.g. (11),9 (12)" and (13)." The phosphine (14) is the starting point of a new
'
Organophosphorus Chemistry, Volume 32 0The Royal Society of Chemistry, 2002 1
+
Organophosphorus Chemistry
2
PhXP@R]
Q-C
3-x
SMe
PBut2
(7) R = H, F or OMe
(6) Ar = p-anisyl
(8)
Ph
(9)R = H or Me F *
/
PhXP@] x )
c
F (11)x = 1 o r 2
3-x3
F
[
(
Ph
(10)
3-n
(12) R = o-Me, p F or H x =o Ir 2
phxpiQ
I
SX
CSF13 (13) x = 0, 1 or 2
approach for the synthesis of the perfluorotail-funtionalised triarylphosphines (1 5), involving the introduction of a silyl group bearing partially fluorinated alkyl substituents, enabling the attachment of 3-9 'remote' solubilising fluoroalkyl tails per phosphorus without compromising the donor properties of the phosphine.I2 A range of polyethyleneglycol-linked diphosphines (16) has also
1: Phosphines and Phosphonium Salts
3
been prepared, having application as reagents in synthesis, e.g. in Wittig reactions under aqueous conditions. The organolithium-halophosphine route has also been used in the synthesis of various heteroarylphosphines, e.g. the diphosphinoterpyridine (17),l 4 the chiral chelating pyridylphosphinocyclopentane (18),lS the atropisomeric bis(dibenzofurany1)diphosphine (19) (and a related sulfonated system),l 6 diphosphino-2,2’-dithienyls,e.g. (2O), l 7 and a range of simple monophosphino derivatives of thiophen, N-methylpyrrole and pyridine.l8 Improved routes to phosphinomethyloxazolines, e.g. (21), have also been described,l 9 and further examples of ‘wide-bite’ diphosphine (and related phosphine-arsine) ligands, e.g. (22),2c22 based on the xanthene backbone, have been prepared. There has been considerable interest in the prepara-
N
R2 Ar2P
PAr,
(21) R’ = H or Me
R2 = H or PPh2
tion of phosphines bearing alkynyl groups as part of the overall structure, not necessarily directly linked to phosphorus. Generation of 1,4-dilithiobutadiyne (from 1,4-bis(trimethylsilyI)butadiyne and methyllithium) followed by treatment with chlorodiphenylphosphine has given the diphosphine (23), of interest as a spacer ligand, used in the synthesis of macrocyclic complexes.23Various phosphadiynes, including the medium-sized heterocyclic systems (24), have been obtained from the reactions of propargyllithium reagents with halophosp h i n e ~Routes . ~ ~ to alkynylphosphines, e.g. (25), of interest for the synthesis of dendrimers, have also been explored.25An aryllithiumxhlorophosphine route has been described for the synthesis of the phosphine (26), which, on heating, or in solution in xylene, is converted into the strikingly red-coloured phosphorane (27), the structure of which was confirmed by an X-ray study.26 Phosphino-alkynylporphyrin systems have also been prepared and used as supramolecular building Full details of improved routes to the azofunctionalised phosphines (28) have now appeared.28 A classical diorganolithium-phenyldichlorophosphine cyclisation is the key step in the synthesis of the 1-benzophosphepines (29).29Metallation of an acetal of o-bromobenzaldehyde, followed by a reaction with trans- 1,2-bis(dichlorophosphino)cyclopentane, has given the diphosphine (30, R = CH(OMe)2), from which the related dialdehyde (30, R = CHO) has been obtained, this having considerable potential for the synthesis of new chiral ‘expanded’ phosphine ligands. Other related systems have also been prepared by this general a p p r ~ a c h . ~Routes ’ for
4
Organophosphorus Chemistry MeC’
O
0
1
Me
Ph (28) R = H, alkyl, NO2 or NMe2
(29) R = H or SiMe3
qR1
PR’R~
OMe
OH
(Me3Si)2CH ,p H
(31) R’ = Ph, Pr’ or But
4
R~ = Ph or P i R3 = But or F R4 = H, Me or But
N(CH2CH2NEt2)2
Me,NA./OR
o-””.
(33) R = H or Me
PPh2
(34)
the synthesis of o-phosphinophenols have undergone further development, and new examples described, e.g. (3 1),31 Treatment of o-methoxyaryllithium reagents with bis(trimethylsilyl)methyldichlorophosphine, followed by reduction of the intermediate monochlorophosphine, has given the new stericallydemanding secondary phosphines (32), from which new ytterbium-phosphido derivatives have been prepared.32 Routes to the amino-functional phosphines (33)33 and (34),34have also been described. Monofunctionalisation by trivalent phosphorus of the calix[4]arene upper-rim has been achieved by lithiation with butyllithium, followed by phosphination with chlor~diphenylphosphine.~~ Interest in the synthesis of chiral phosphinoferrocene systems has been maintained, and a considerable number of new systems described. Several reports of
I : Phosphines and Phosphonium Salts
5
f12 PPh2
Fe
Fe
(37)R = Me, Pr', NMe2 or N-pyrrolidinyl
(35) .PPh;! V
PPhp I h Fe
Fe
&.Me Ph (39) R = Me or Pr'
(40) Ar = Ph or o-anisyl
(41)
the synthesis of chiral oxazolinylferrocenylphosphines have appeared.3c38 Surprisingly, the C2-symmetric system (35) fragments to form the fulvene system (36) on protection of the phosphine as its sulfide.38Among new chiral phosphinoferrocenes described are (37),39 (38),40(39):l (40)42and (41).43The ortho-lithiation of 1,l'-dibromoferrocene, using lithium diisopropylamide has been reported for the first time, enabling access to a range of new phosphinoferrocenes, e.g. (42)44 and (43).45The organolithium-chlorophosphine route has also been applied in the synthesis of the new ferrocenophane systems (44)46947 and (45);' and in the synthesis of other phosphinometallocene systems based on chromi~m:~titanium5' and zirconium.51 Both organolithium and Grignard reagents have been employed in a stepwise synthesis of the chiral phosphine (46) from (-)menthy1 chloride. The PPhp
Fe
&Br
(42)
ie
&Br
(43)
R &p-R (44) R = (-)-menthy1
(-)-bornyl or NPt2
6
Organophosphorus Chemistry
.. (-)-Men'
( a v o : \
P AFI. ' Ph
Rn-P(CH2CH2(CF2)xCF3)3-n
(46) FI = fluorenyl
(-)-Men = (-)-menthy1
H
(48)
(47)
R = (-)-rnenthyl, cyclohexyl or Pr n = 1 or2 x = 5-7
H
H
H
H
(50)M = Si or Ge
diastereoisomers of (46) were obtained via fractional crystallisation of the borane adducts, followed by decomplexation, and shown to undergo an unusual crystallisation-induced asymmetric transformation upon slow evaporation from refluxing h e ~ t a n eGrignard .~~ reagents have also been employed in the synthesis of the diphosphine (47),53 and a series of alkylphosphines bearing partially perfluorinated substituents, e.g. (48).s4,ss The organozirconium reagent (49) is a key intermediate in the synthesis of bisphospholane systems, e.g. (50). s6 Organolithium, -magnesium and -sodium reagents have been used to prepare various new carboranylphosphines.s7-s9 1.1.2. Preparation of Phosphines from Metallated Phosphines. As in previous years, the use of lithiophosphide reagents continues to dominate this approach to phosphine synthesis. The 1-(9-anthracenyl)phosphirane ( 5 1) has been obtained in two steps by lithium aluminium hydride reduction of 9-anthryldichlorophosphine, and subsequent lithiation and cyclisation with 1,2-dichloroethane. This compound is quite stable, resisting attempts to form polymers by ring-opening of the phosphirane system.60The reactions of lithium diphenylphosphide with tosylate substrates have been used in an improved route to the chiral aminoalkylphosphine (52), derived from L-valine,61from which a series of new chiral phosphine ligands, e.g. (53), has been derived, and also to the phosphinoalkyloxazoline system (54).62 Stepwise substitution of a ditosylate
(54) R = Ph, I-adamantyl, But
or 3,5-But2C6H3
(55) R' = Me or I-naphthyl
R2 = Ph or p-anisyl
I : Phosphines and Phosphoniurn Salts
(59) n = 1 or 4-7 R = Pr' or Ph
7
(60) R =
or CgH19 n = 1-5, 11 or 13
derived from tartaric acid with lithium amide reagents, followed by lithium diphenylphosphide, has given a series of chiral aminoalkylphosphine ligands (55).63,64 The phosphinoarenetricarbonylchromium system (56) has been prepared by treatment of a related arylcarbamate substrate with lithium diphenylph~sphide.~~ Among new monophosphines prepared by the reactions of lithiophosphide reagents with chloroalkyl substrates are the phosphinomethylpyrazole (57),66 the mixed donor phosphines (5S),67 (59)68and (60),69 and the phosFhinoalkylcyclopentadienide system (6 1).70 Systems of the latter type have also been accessed by several groups via the ring-opening of spiro[2,4]hepta-4,6-dienes with lithium d i p h e n y l p h ~ s p h i d e . ~Among ~ - ~ ~ this series of anionic phosphine ligands is the indenyl system (62).74 One such system derived from potassium diphenylphosphide has been shown to involve coordination of a neutral phosphine functionality to the potassium ion.75 Phosphide-induced ring-opening of oxetanes has enabled the synthesis of functionalised neopentylphosphines, e.g. (63).76The generation of lithiophosphide reagents by cleavage of phenyl groups from a,o-bis(diphenylphosphin0)-
6..@ SR1 Pi
PhP-(C H2)n- PPh I I H H
'-OH PRg
PPh2
(62)
(63) R1 = lndenyl or fluorenyl R2 = Ph or Et
Ph
Ph.
'P
L
O
n =2or3 (66)
n =I-5 (64)
8
Organophosphorus Chemistry
alkanes on treatment with lithium in THF has received further study and optimised procedures developed, using low temperature conditions,7777g assisted by u l t r a ~ o u n dresulting ,~~ in improved routes to a,o-bis(pheny1phosphino) alkanes (64), and hence to new diphosphines, e.g. (65)79 and (66).80 Monolithiated a,o-bis(phosphin0) alkanes have been used in the synthesis of novel diblock copolymers bearing bidentate phosphine sites." A dilithiophosphide reagent derived from 1,2-bis(phenylphosphino)benzene has been used to prepare the chiral macrocyclic, atropisomeric binaphthyldiphosphines (67)-s2 Among other new diphosphines prepared via lithiophosphide agents are the atropisomeric C2-symmetric 3,3'-bisindolizine system (68),83 the pincer-system (69),84 the diphosphinoheptalene (70),85 a series of bis(phosphinoalky1) bipyridyls (7 1),86 and the bis(phosphinoaryl)calix-[4]-arenes (72), from which
Ar2P (67) R = H, Ph, 4-biphenyly1, 2-benzofuranyl or 2-naphthy1
(68) Ar = Ph or 0-tolyl
(69)
R' = H or OCH2Ph
R~ = cyclopentyl PPh2
I
PPh2
PPh2
PPh2
1 (70) R = Ph
(71) n = 1-3
OH (72) n = 1 or 2
novel water-soluble diphosphines have been prepared by multiple sulfonation under conditions that do not cause oxidation at phosph~rus.'~ The reactions of lithiophosphide reagents derived from 1,2-bis(phosphino)benzene with cyclic sulfate esters are the basis of the synthesis of various chelating diphosphines bearing chiral heterocyclic phosphine substituents, e.g. the 1,2bis(phosphetan0)benzene (73)," and a related series of 1,2-bis(phospholano)benzene^,^^-^^ e.g. (74).92In related work, the chiral phospholanes (75) have been prepared by sequential reactions of lithio(trimethylsily1)phosphide re-
1: Phosphines and Phosphonium Salts
9
R
&Ph
HO-
R (74) R = Me or Et
(73) R = PhCH2
(75) R = Me, Et or Pr‘
(77) R‘ = alkyl or Ph R2 = alkyl
agents with cyclic sulfate esters and subsequently employed in a lithiophosphide route with acyclic chiral tosylates to give a series of bisphospholanes having chiral back-bones, e.g. (76).93 Treatment of chiral cyclic sulfates with lithium diorganophosphides in a one-pot process has provided a direct route to the chiral diphosphines (77).94 Chiral 1,l’-bis(phosphetano)ferrocenes (78), have been prepared by two groups, using the lithiophosphide4yclic sulfate m e t h ~ d .Cyclooligophosphines, ~~?~~ (ArP),, (n = 4 6 ) , have been obtained by oxidation of monolithiated primary phosphines using benzophenone in THF at room t e m ~ e r a t u r e .The ~ ~ reactions of dilithiated primary silyphosphines with diorganodichlorosilanes, which give new organosilyl-phosphorus systems, have been reviewed.” The new sterically hindered tripod ligand (79) has been obtained from the reaction of lithium diphenylphosphide with a trifunctional bromo~ilylmethane.~~
@II
Fe
H
I
,p? R
I
c
Me2SizMe>SiMe2 Ph2P
I
PPh2
PPh2
R (78) R = alkyl
(79)
Sodio-organophosphine reagents have also found considerable use in the past years. Aminyl radicals, R2N, are involved in the photo-assisted radicalnucleophilic substitution reactions between sodium diphenylphosphide and Ncyclopropyl-N-ethyl-p-toluenesulfonamidein liquid ammonia, which after oxygenation, leads to the aminoalkyldiphosphine dioxide (80) as the principal product. loo The reactions of sodio-organophosphide reagents with chloroalkyl
Organophosphorus Chemistry
10
Me2PCH2CH2SR
(81) R = Me, Et or Ph
(83) R' = H or Me
R2 = Ph or Cy
substrates are the key steps in the synthesis of the thioethylphosphines (8 l), lo' and the new chiral diphosphine (82).'OZ A sodium diorganophosphide-tosylate or mesylate route has been employed in the synthesis of the chiral pyrrolidinophosphines (83)'03 and the chiral oxazolinyl system (84).lo4 Displacement of the chloride from a chloroarene is the key step in the synthesis of the chiral tetraphosphine (85). lo' Sodio-organophosphide reagents also promote ringopening of epoxides, enabling the synthesis of a range of chiral P-hydroxyet hylphosphines, 1oc108 e.g. (86) O7 and (87). O8
&$
Ph2P
I
Boc (84) R = Ph, P t or But
P h 5, P T O H R
OH
(86) R = Ph or Me
Potassium organophosphide reagents also continue to find applications in synthesis. Direct displacement of fluoride from fluoroaromatic substrates by potassium diphenylphosphide is the key step in the synthesis of the phosphinoarylsulfoxides (88),'09 water-soluble phosphino-amino acid systems, e.g. (89),"' and the chiral benzoxazine system (90)."' Related displacement of fluoride by potassium monophenylphosphide has been used to prepare a series of hydrophilic triarylphosphines, e.g. (9 1). l 2 Among new phosphines prepared by conventional displacement reactions by potassium diphenylphosphide on
I : Phosphines and Phosphonium Salts
11
0
Ph2P
PPh2
(88) R' = H or Me R2 = H or Me R3 = H or OMe
o-""" OMe
(91) X = COOH or NH2
t
(92)
pih
RiR2N
PPh2
(93) R' = Me or Ph R2 = Ph CI
Ph2P
PPh2 CI
(94)
(96)
(95)
alkyl halides or sulfonate esters are (92),' l 3 the chiral aminoalkylphosphines (93),'14 the chiral chelating diphosphines (94),'15 (95)'16 and (96),'17 and a diphenylphosphinoalkyl-functionalisedsilsesquioxane system. The reactions of potassio-phosphide reagents derived from primary (ortho-substituted)arylphosphines with cyclic sulfate esters have given the chiral phospholanes (97).'19 The heterocyclic system (98) is formed in the reaction of t-butylphosphonic dichloride with the dipotassium salt of the diphosphine ButPH.PHBu'. I2O Generation of metallophosphide reagents directly from red phosphorus in the presence of alkyl halides has been utilised in a two-step route to P-substituted alkylphosphines (99).'*' Interest in the isolation and structural characterisation of metallo-organophosphide systems continues to grow. Studies of the structures of alkali metal-
''
(97) X = H, OCH2Ph, CH20CH2Ph or CH20Me
(98)
(99)
Organophosphorus Chemistry
12
rich polyanionic phosphides have been reviewed,122 and new structural investigations of associations of bulky mono-organophosphide ions, RP2-, with lithium, sodium and copper(1) cations reported. 123 The solid state structure of a dioxane solvate of potassium diphenylphosphide involves a three-dimensional network involving anion-cation interactions. 124 The influence of donor solvents on the solid state molecular structure of KP(But)Ph has been studied.'25 Structural studies of crown ether adducts of caesium salts of bulky primary arylphosphines have been reported. 126 New lithiophosphide systems have been obtained from the reactions of lithium bis(trimethylsily1)phosphide with benzonitrile, and structurally characterised. 127 Magnesium organophosphide systems have been prepared by treatment of (triisopropylsily1)phosphine with dibutylmagnesium. 128 A lithiophosphide involving a silyl(bisbory1phosphide) anion has been characterised. 129 Further studies have been reported of the characterisation of phosphido derivatives of the heavier elements of main groups 13, 14130 and 15.131 The aluminium phosphide system ( B u ' ~ A ~ P H ~ ) ~ has been prepared and used as a mild phosphanylation reagent for the transfer of PH2 units to group 14 elements.132The application of zirconium organophosphide reagents in synthetic chemistry has been reviewed,133 and further studies of the reactivity of the zirconium-phosphorus bond have appeared. 347135 Applications in synthesis of phosphines metallated at carbon also continue to appear. The chemistry of metal cyclopentadienyl systems bearing pendant phosphorus donors has been reviewed. 36 The lithium diphosphinocyclopentadienide (100) is a key reagent for the synthesis of new polyphosphinoferroc e n e ~ Treatment . ~ ~ ~ of the ferrocenophane (44, R = Ph) with phenyllithium generates the C-lithiated ferrocenylphosphine (101), from which a range of new unsymmetrical diphosphorus donor systems has been prepared. 138 A study of the reactivity of the phosphinosilylcyclopentadienides (102) towards Me
Li+
@
Li
Me (102) R = Cy or Mes
zirconium tetrachloride has revealed unexpected P-Si and P-C bond cleavage p r o c e ~ s e s . 'Treatment ~~ of diphenyl(2-pyridylmethy1)phosphine with butyllithium results in metallation at the methylene group to form the reagent (103) from which the alkoxysilyl-terminated phosphine (104) has been prepared, this compound subsequently being tethered to a silica-supported palladium catalyst. 140 Lithiation of diphenyl(2-pyridy1)phosphine occurs at the 2-position of the pyridine ring; subsequent treatment with electrophilic reagents has given a range of new phosphines. 14' Lithiation of the (-)-menthy1 ester of 2-(dipheny1phosphino)propanoic acid, followed by alkylation with benzyl bromide,
1: Phosphines and Phosphonium Salts
13 CH2Ph I
O y H - P P h 2 Li
Q&pph2
\
Me-C-COOH PPh2 I
(CH2)3-Si(OMe)3
and ester cleavage, provides a route to the chiral system (105), isolated in 70% yield and >%YOenantiomeric excess as the (+)-lS-i~omer.'~~ Two reports of the deprotonation at carbon of methylphosphine-borane systems have appeared. Treatment of the chiral system (106) with secondary butyllithium, followed by addition of an epoxide, results in the formation of the chiral borane-complexed phosphino-alcohol(lO7), from which new chiral phosphitophosphino ligands have been prepared.143 Enantioselective deprotonation of the phosphine-boranes Ar(Me)2P(BH3with cyclopentyllithium in the presence of (-)sparteine, followed by treatment with benzophenone, has given the chiral system ( 108).14 Several solid state structural studies of phosphines
(106) R' = Ph, o-anisyl
(107) R2 = M e or Ph
or I-naphthyl
metallated at carbon have also a ~ p e a r e d . ' ~ ~ A-theoretical '~~ study of diphosphinomethamide systems coordinated to main group 14 elements in their +2 oxidation states has also been reported. 14* 1.1.3 Preparation of Phosphines by Addition of P-H to Unsaturated Compounds. A comprehensive review of addition reactions of P-H compounds of many types contains much that is relevant to this ~ e c t i 0 n . lAddition ~~ of secondary phosphines to aryl(diviny1)phosphines under base-catalysed or freeradical conditions has given a range of new triphosphines (109).'50 The polyether-functionalised diphosphines (1 10) have been obtained from the photochemically initiated addition of vinyl ethers to 1,3-(bisphosphino)propane.15' Addition of allyl alcohol and 1,4-pentadiene to the bis(phosphino)cyclopentane (1 11) has provided the new chiral diphosphines, (1 12) and (1 13), respectively. 52 Bis(2-phenylethy1)phosphines have been shown to react both chemo- and regio-selectively with phenylcyanoacetylene to give the Z-cyanovinylphosphines (1 14).153 Phosphinoalkyl-functionalised silsesquioxanes'54 and alkoxysilanes' 55 have also been obtained by addition of secondary phosphines to appropriate alkenyl-functionalised precursors. Metal ion-catalysed additions have also been reported. Cyclopentadienyl-lanthanum complexes have been shown to promote the intramolecular hydrophosphinationsyclisation of phosphinoalkenes and phosphinoalkynes. Thus, e.g. the phosphine (1 15) is converted to the phospholane (1 16).'56 Secondary phosphines bearing allyl
'
Organophosphorus Chemistry
14 RO CH2C H2PR2 Ar-P 'CH2CH2PR2
RO
OR
( 1 1 0 ) R = E t , Bu,Bu'otCy
GPH2 u. 'PH2 'PH2
(1 11)
(\/OH
(PhCHRCH&P-C(Ph)=CCN
(114) R = H or Me
substituents have been shown to undergo a cyclotrimerisation reaction at a cyclopentadienyl-iron template to form the triphosphorus macrocyclic system (1 17).157A macrocyclic polyphosphine involving 12 phosphorus atoms in a 36membered ring has been obtained from the radical-promoted reaction of phenylphosphine with phenyl(diviny1)phosphine complexed to a gold thiolate cluster. 58 A chiral platinum complex-catalysed asymmetric hydrophosphination of activated alkenes, e.g. acrylonitrile, with secondary phosphines of the type HPRPh has given the chiral phosphines (1 18) with control of stereochemx
P
R'PPh R2 (1 16)
(117) R = H or Ph
(118) R' = Pr', Cy, But, Me
o-anisyl or Mes R2 = H or alkyl X = CN or C02R
istry at phosphorus or carbon centres.159Hydroformylation of P-H bonds continues to find application in the synthesis of water-soluble phosphines, e.g. (1 19)l6' and (120),l6' the latter also capable of being anchored to a peptide via the carboxylic acid functionality. A series of water-soluble heterocyclic phosphino-amino acid salts (121), white, air-stable crystalline solids, has been obtained from the reactions of primary phosphines bearing bulky aryl groups with alkali metal glycinates and formaldehyde.'62 New 4-phosphino- 1,3,2dioxaborinanes (122) have been prepared from reactions of secondary phosphines with salicyaldehyde in the presence of phenylboronic acid esters.163 Examples of the addition of P-H bonds of phosphines to C=N have also been reported. 164-166 Thus, e.g. the chiral phosphino-functionalised chromocene system (123) has been obtained by addition of diphenylphosphine to an imine precursor. 166
1: Phosphines and Phosphonium Salts
15
wC02
cr
(HOCH2)2PvP(CH20H)2
'1
/- co2-
Ar-PrN)
HOH2C'I HOH2C
2M' L
p\
I
N
Lcop-
CH20H CH20H
(121) Ar = Ph, Mes or
(120)
M = Na or K
F:
co I co co (1 12) R = alkyl or Ph
(123) Y = Me, M e 0 or CI R = Me, CH,C02Me, p-anisyl or Ph
1.1.4 Preparation of Phosphines by Reduction. Trichlorosilane remains the most commonly used reagent for the reduction of phosphine oxides to phosphines, and has been widely applied in the synthesis of a range of new systems. A developing theme is the introduction of the diphenylphosphinyl group into an aromatic system by palladium-catalysed displacement of an aryl triflate functionality derived from a phenol, by diphenylphosphine oxide, followed by trichlorosilane reduction. Among new phosphines prepared in this way are the atropisomeric systems (124),'679'68(125),'69 (126; R = Ph)170 and (127).17' The biferrocenyldiphosphines (128) have been obtained by Ullmann coupling of o-iodoferrocenylphosphine oxides in the presence of copper,
Q
moMe PAr,
:Ph2 \
(124) Ar = Ph or p-CF&H4
PPhR
Fe 'PPhR Fe
(127) R = Ph, Pr'or CMe20SiMe2Bu' n = 1 or2
(128) R = 2-biphenylyl or 1-naphthyl
/
16
Organophosphorus Chemistry
Ph2P I
PPh2 I
Ph2P I
Ph2P
PPh2
PPh2 I
Ph2P
PPh2
(130)R = n-C6HI3
followed by final reduction with trichlorosilane and separation of enantiomers via borane complexation. 172 Palladium-catalysed Suzuki-coupling of the chiral diphosphine oxide (129) with p-dibromoarenes, followed by trichlorosilane reduction, has given a route to the rigid poly (BINAP) system (130).'73 Ullmann coupling of p-bromophenylphosphine oxides with perfluoroalkyl iodides has given the related p-perfluoroalkylphenylphosphine oxides, from which the phosphines (13 1) have been obtained on reduction with trichlorosilane in t01uene.l~~ Trichlorosilane has also been used in the final stage of the synthesis of a range of polyphosphines linked via alkyne bridges, e.g. the pincer-systems (132),'75 and related dendrimer core structures, e.g. (133).'76 Phosphine oxide groups attached to the lower rim of calixarene systems have been reduced by phenylsilane. 77 Hydrido-aluminium reagents have also attracted attention for the reduction of phosphine oxides, phosphonate esters, phosphinyl halides and halophosphines. The alane system, essentially AlH3 (from treatment of lithium aluminium hydride with concentrated sulfuric acid in THF), has been shown to be effective as a chemoselective reducing agent for phosphine oxides, enabling reduction to the related phosphines in the presence of other reactive groups (apart from aldehydes, ketones and disulfides).178 Reduction of alkylphosphonate esters to primary alkyl phosphines has been
1: Phosphines and Phosphonium Salts
(131) n = 1-3
17
(131) n = 1 o r 2
achieved with lithium aluminium hydride, enabling the isolation of the This bis(primary phosphines) (134) as air-stable, pale yellow solids.1617179 reagent has also been used to reduce chlorophosphines to form new secondary phosphines bearing perfluoroalkyl substituents, 180 and both phosphine oxide and phosphinyl chloride functionalities in the synthesis of the macrocyclic system (135).181 Reduction of chlorodiphenylphosphine with a variety of metals, followed by in-situ protonation of the intermediate metallophosphides, has also been reported. The use of activated zinc in THF was found to be the most effective system.182 Me
PH2 H2P
(134)n = O o r 1
Me (135)
1.1.5 Miscellaneous Methods of Preparing Phosphines. Approaches to the synthesis of specific types of organophosphine have been reviewed, covering phosphinoaryloxazolines, 83 trans-2,5-disubstituted phospholanes, 84 new chiral phosphines which have been reported since 1990,185 chiral hydroxyphosphines, 186 and phosphorus-sulfur donor ligands.187 The uses of phosphine (PH3) in the synthesis of organophosphines has also been reviewed.'88 A direct route for the synthesis of arylphosphines is offered by the reaction of
'
'
Organophosphorus Chemistry
18
Ph2P
R
\
ph2p%
(137) R = Ph, Pr' or But
(136)
diphenylphosphine with phenolic triflates, catalysed by nickel(I1)diphosphine complexes in the presence of a base in DMF at ca. 120". This approach has been applied in the synthesis of the atropisomeric system (126, R = Me or Ph), 89-19 the steroidal BINAP system (136),'92 and the hybrid donor system (1 37).193 A related reaction involving chlorodiphenylphosphine instead of diphenylphosphine has been used to prepare the diphosphine (138).'94 Direct phosphination of iodoarenes using diorganophosphines, catalysed by palladium acetate, has been used in the synthesis of the functionalised phosphines (139)'95 and ( 140).'96An even more straightforward route to arylphosphines is provided by the reaction of bromoarenes (bearing a wide variety of other functional groups) with triarylphosphines in DMF at 1lo", catalysed by palladium acetate. 197 A related reaction of triarylphosphines with aryl triflates has been used to prepare atropisomeric systems, e.g. (141).'98 The phosphinoarylboronic acid (142) has been shown to undergo palladium-promoted biaryl coupling to a dibromo-o-phenanthroline to give the polydentate hybrid ligand (143) (after dealkylation of the methyl ether group).'99 Enol triflates
' '
PR2
I
PPh2 PPh2
Me0
PhnP
3-n
M e J $ q o M e 0 (139)
n = 1or2
(140) R = Et or Ph
&&
PAr2
\
(141) Ar = Ph, ptolyl or
p-anisyl
/
PPh2
Ph2P (143)
1: Phosphines and Phosphonium Salts
19
Mel ,But Ph,
,BH3
OMe But
Me
have also been shown to undergo palladium-promoted phosphination with diphenylphosphine, enabling the synthesis of vinylphosphines from ketones bearing an a-hydrogen.200 Routes to chiral, borane-protected secondary phosphines (144) have been developed,201 ,202 enabling the synthesis of a range of new chiral tertiary phosphines, e.g. (145),202 via lithiophosphide routes. Sequential treatment of diastereoisomerically pure oxazaphospholidineboranes with different organolithium reagents provides a route to chiral phosphine-borane adducts, e.g. (146).203 Many new tertiary phosphines have been prepared by synthetic elaboration of simpler organophosphines which does not involve the phosphorus atom. Chiral phosphines bearing heterocyclic substituents have been obtained by elaboration of arylphosphines bearing amino, carboxaldehyde or nitrile groups, respectively, giving, e.g. the pyrrolidinyl system (147),204phosphinooxazolidines,205,206 e.g. (1419,~'~ phosphino-oxathianes, e.g. (149),207 phosphino-oxazines (150),208 and the phosphino-oxazolines (15 1).209Wittig reac-
(147) R = Me or Et
tions of p-diphenylphosphinobenzaldehyde with a,o-diphosphonium salts have given a series of bis(phosphinophenyl)polyenes, e.g. (152).2107211 Further examples of the synthesis of iminophosphine ligand systems by Schiff's base formation involving phosphinobenzaldehydes or phosphinoarylamines, have appeared,212-216 and this route has been extended into the organometallic area with the preparation of the benzenechromium tricarbonyl derivatives (153), which exhibit planar chirality.217New phosphinobenzenechromium tricar-
20
Organophosphorus Chemistry PPh2
Ar(CO),
'R3
(153) R' = Me or Ph
(152) n = 0-3
R2 = H, Me or Ph R3 = H or Me
bony1 and phosphinoferrocene systems, e.g. (154),218 (1 55)219 and (156),220 have also been prepared by side-chain elaboration. The macrocycle (157) has been obtained from a high dilution base-catalysed cyclocondensation of The phosphenyl bis(2-mercaptoethy1)phosphine and 1,2-di~hloroethane.~~~ phinoalkylthiourea (158) is formed in the reaction of 2-aminoethyldiphenyl-
0 (155) YR = OMe, OEt, OPr"
(156)
NHCH2CH20H
c5
or NH(CH2)30H
Ph
S
S I1
Ph2PCH2CH2NH-C-NHPh
WS
phosphine with phenylisothiocyanate.222Treatment of both cyclic and linear halogenophosphazenes with p-hydroxyphenyldiphenylphosphine in the presence of caesium carbonate has given phosphinoaryl-functionalised phosphaz e n e ~A . ~review ~ ~ of the synthesis of homogenised-heterogeneous catalyst systems includes coverage of the use of silane-functionalised phosphines for binding to silica surfaces,224and new approaches to this topic have been A combinatorial approach to the synthesis of phosphinefunctionalised peptides has been described, based on incorporation of the Nprotected phosphine sulfides (159), followed by d e ~ u l f u r i s a t i o nThe . ~ ~ ~chiral diphosphinopyrrolidine (160) has been coupled to a polyacrylic acid via nitrogen to give a new, water-soluble, polymeric ligand.228Amide formation involving a variety of amino-functional phosphines has been widely employed
1: Phosphines and Phosphonium Salts
(159) R
21
= Ph or Cy
(161) R = H or Me Pr' Y N H X
PPh2
0)-NbPPh2
a ($ P;'
(163)X =
,
or
7"'CH
3
in the synthesis of new systems, including ( 161),229air-stable primary phosand the C2-symmetric diphosphines (163).232Acylation phines, e.g. (162),2303231 of chiral hydroxyalkyl or hydroxyaryl phosphines with o-sulfobenzoic anhydride has given new water-soluble l i g a n d ~The . ~ ~reactions ~ of hydroxymethylphosphines with primary and secondary amines continue to find application in the synthesis of new aminomethylphosphines. In the past year, this approach has been used for the synthesis of dendrimeric water-soluble p h o ~ p h i n e s and ,~~~ new e.g. (164),238 used in the synthesis of macrocyclic dimetallo-complexes. A new route to (ferrocenylmethy1)diphenylphosphine is offered by the reaction of (hydroxymethy1)diphenylphosphine with (ferrocenylmethyl)trimethylammonium iodide.239The chiral phosphine (165) is formed similarly in the reaction of a related ammonium salt with tris(hydro~ymethy1)phosphine.~~~ An improved route to the phosphine (166)
Ph2P-N H
/O^o-H
has been developed, involving metallation of o-bromophenyldiphenylphosphine, followed by treatment with diethyl c h l o r ~ p h o s p h a t eThe . ~ ~ synthesis ~ of various water-soluble phosphines has been reported, including the wide-bite system (167),242 a disulfonated triphenylphosphine (free of phosphine oxide contaminant^),^^^ and the cationic phosphine (168) in an improved route.244
Organop hosphor us Chemistry
22
\
Ar = ~ O - ( C H 2 ) ,~ S 0 3 N a
/
Ar2P
PAr2 (167)
+
Ph2PCH2CH2NMe3 1 (168)
n =0,3or6 R2P-CH=N
+
Pr2’ X -
(169) R = Pr2’Nor Cy2N
R2P-CH 0 (170)
Treatment of the phosphino-iminium salts (169) with potassium hydroxide in THF affords the formylphosphines (170), which are remarkably stable in solution compared with the related phosphine Phosphines bearing aminoyl radical substituents, e.g. (171), have also been The phospha[3]triangulane, (172), has been obtained from the reaction of bicyclopropylidene with a metal complexed p h e n y l p h ~ s p h i n i d e n eThe .~~~ phosphinotrithiacyclophane (173) has been prepared by the base-promoted reaction of
kPPh I
0(171)
tris[(2-chloromethyl)phenyl]phosphine with 1,3,5-tris(mercaptornethyl)benzene. This system exhibits ‘in-out’ conformational isomerism, centred around pyramidal inversion at phosphorus. Inversion barriers and the reactivity of the conformers have also been s t ~ d i e d . ~Resolution ~ ~ , ~ ~ ’ of the 2,2’-biphospholene (174) has been achieved via chiral palladium complexes.251An electrochemical route to phosphines bearing heteroaryl substituents, e.g. pyridinyl, pyrimidyl and pyrazolyl systems, has been developed which entails a nickel complexcatalysed electroreduction of halogenophosphines in the presence of bromo (heter~)arenes.~’~ The single-electron reduction of phosphorus trichloride has been studied with a view to the generation of intermediate radical cation species for the synthesis of organophosphorus compounds.253 A photochemical route to tris(di-t-buty1phosphino)phosphine has been developed, this compound being shown to contain a planar central phosphorus atom.254
1:Phosphines and Phosphonium Salts
(174)
23
(175) R =Me or Ph X=HorF
Among new phosphines prepared via reactions of phosphines coordinated to metal ions are the diphosphinonaphthalenes (175),255and the iminophosphine (176).256 1.2 Reactions of Phosphines. - 1.2.1 Nucleophilic Attack at Carbon. Treatment of the unsaturated y-lactone (1 77) with tributylphosphine results in selective relacement of chlorine to form the phosphonium salt (178).257 Reactions of phosphines with alkynes have continued to attract interest. A palladium-catalysed addition of triphenylphosphine to unactivated terminal alkynes in the presence of methanesulfonic acid provides a route to the vinylphosphonium salts (179). This reaction fails with methyldiphenylphos-
RYx (179) R = alkyl
phine or tributylphosphine. Related reactions with fully substituted alkynes have also been explored, and provide novel routes to phosphonium salts.258 The generation of reactive zwitterionic intermediates by addition of phosphines to alkynes bearing electron-withdrawing groups has continued to be a useful synthetic approach, having been used in the preparation of functionalised ally1 c a r b ~ x y l a t e sand , ~ ~for ~ the generation of ylides which subsequently undergo intramolecular Wittig reactions, resulting in fused dihydrofurans,260 and highly electron-deficient 1,3-diene~.~~l Protonation of the zwitterion resulting from addition of triphenylphosphine to dimethyl acetylenedicarboxylate, by 2-hydroxyacetophenone, leads initially to a vinylphosphonium salt which undergoes an aromatic electrophilic substitution reaction with the conjugate base of the hydroxyacetophenone to give vinyl-substituted systems, together with 8-acetyl-4-methoxycarbonyl-2-chromone.262 Treatment of di-tbutyl acetylenedicarboxylate with triphenylphosphine in the presence of a series of heterocyclic N-H acids, e.g. imidazoles, triazoles or carbazoles, has given a series of highly hnctionalised stabilised ylides, e.g. (1 Related reactions in the presence of fluoropentane-2,4-dione result in the formation of the betaines (181),264 and, in the presence of c60, in a series of fullerenes containing phosphonium ylide f ~ n c t i o n a l i t y .Treatment ~~~ of a-zirconated phosphines, e.g. (182), with acetylenic reagents results in intramolecular coordination of the negative centre of the initially formed phosphonium zwitterion to the zirconium, acting as an electron-acceptor, to form cyclic
Organophosphorus Chemistry
24 0
0
HC-CO2R
Ph3P
I
HC-CO2R I
+PPh3 (181) R =Me, Et or But
systems, e.g. (183).266,267 The phosphine (184) is reported to be formed in the reaction of tributylphosphine with diphenylacetylene.268Tributylphosphine has been shown to catalyse the dimerisation of activated alkenes under ambient temperature and pressure conditions.269Dipolar adducts of triphenylphosphine with allenic esters undergo an unusual [8+2] annelation with tropone, leading to 8-oxabicyclo[5,3,0]-deca-l,3,5-trienes.270 The reactions of trialkylphosphines with methoxyallene have been investigated, with the identification of various betaine and ylide products.271The betaines (185), formed in the reactions of triphenylphosphine with polymer-bound 1,2-diaza-1,3-butadienes, undergo cleavage in methanol to provide a solid-phase synthesis of the heterocyclic stabilised ylides (186).272Tributylphosphine has been shown to catalyse the acylation of benzylic alcohol end-groups in rotaxane systems, in the presence of 3,5-dimethylbenzoic anhydride.273 0
1
Ph3P
0 +N
I
R
(186) R = H or COR
1.2.2 Nucleophilic Attack at Halogen. Two groups have reported studies of the adducts of trialkylphosphines with iodine. Both 1:1274 and 1:2274,275 phosphine-iodine combinations have been characterised, the former having an ion-pair structure whereas the latter are predominantly ionic, involving discrete R3PIf and I3- ions. Structural studies reveal weak iodine-iodine interactions between cation and anion in the latter type and also subtle structural variations depending on the nature of the substituents at phosphorus.27 The reactions of benzoin with the t riphenylphosphine-br omine adduct, under various conditions, have been investigated.276The mechanism of formation of diphenyltrichloromethylphosphine in the reaction between diphenylphosphine and carbon tetrachloride has been investigated, and shown to be multistep, involving the intermediacy of chlorodiphenylphosphine and
1: Phosphines and Phosphonium Salts
25
tetraphenyldipho~phine.~~~ A kinetic study of the reaction of tertiary alcohols with the triphenylphosphinexarbon tetrachloride system in various solvents has been reported, and pathways leading to both substitution and elimination products identified.278The triphenylphosphine-carbon tetrachloride system has also found use in the synthesis of 1,l-diheter~arylethylenes.~~~ A convenient route to dialkyl carbonates is provided by the reactions of primary alcohols with carbon dioxide, in the presence of a tributylphosphine-carbon tetrabromide-guanidine base system.280The reagent Ph3P(SCN)2 can be generated in situ from treatment of the triphenylphosphine-bromine system with ammonium thiocyanate in acetonitrile at room temperature, and has been used for the direct conversion of alcohols to alkyl thiocyanates in excellent yield, with very little contamination by the related isothiocyanates.281This reagent has also been used for the conversion of alkyl- and aryl-silyl ethers to the related thiocyanates.282A mild and efficient conversion of carboxylic acids to acid chlorides is offered by use of the cyanotrichloromethane-triphenylphosphine system.283The solid-state reaction between triphenylphosphine and chloramine has been studied by thermal analysis techniques, together with 31P NMR.284A combination of triphenylphosphine with N-halosuccinimides in refluxing dioxane offers a reagent for the conversion of hydroxyazines into the related heteroaryl chlorides.285The reactions of tritylphosphine (and secondary phosphines bearing a trityl group) with phosgene give the related, surprisingly stable, monochlorophosphines.286The iodotrimethylsilane-triphenylphosphine combination has been used to promote the facile dealkylation of Tris(perfluoroalky1)difluorobenzyl esters of cephalosporin carboxylic phosphoranes are formed in the electrochemical fluorination of trialkylphosphines.288 1.2.3 Nuckophilic Attack at Other Atoms. Phosphorus(II1)-bridged [ llferrocenophanes, e.g. (44, R = Ph), do not undergo transition metal-catalysed ringopening polymerisation. However, if the phosphorus lone pair is protected via formation of borane adducts, polymerisation can be achieved.289The reactivity of the boron-hydrogen bonds of phosphine-borane adducts has been reviewed.290The intermediacy of fluoroborane-phosphine adducts in the deprotection of borane-phosphine adducts using fluoroboric acid has now been confirmed by NMR studies.291A procedure has been developed for the oxidation of secondary and tertiary phosphines using oxygen (or air) in the presence of a catalytic amount of cobalt@) acetylacetonate, and 3-methylbutanal, which acts as a sacrificial aldehyde. A supported, re-usable catalyst for the oxidation of triphenylphosphine was also developed.292 A nickel(o) complex-catalysed oxidation of tertiary phosphines in the presence of nitrous oxide has been described, the key point being the activation of nitrous oxide in the coordination sphere of the Conversion of polykis(dipheny1phosphino)benzenes (Ph2P)&H6 --n [n = 2-41 to the related phosphine-sulfides and +elenides has been reported, together with 31Pand other NMR parameters.294 A kinetic study of the reactivity of a wide range of trivalent phosphorus compounds with elemental sulfur has been reported, together with related
26
Organophosphorus Chemistry
reactions involving carbon d i ~ u l f i d e Triphenylphosphine .~~~ has found use in the synthesis of nucleosides via cleavage of S , S - d i s ~ l f i d e s Cleavage .~~~ of selenium-selenium and tellurium-tellurium bonds on treatment of phenylselenium- and phenyltellurium-iodine adducts with triphenylphosphine has also been reported, giving rise to the charge-transfer complexes (187).297,298 Phosphine-induced cleavage of silicon-oxygen bonds is involved in the catalysis of the aldol reaction between ketene silyl acetals and aldehydes.299 Further studies of the involvement of radical species in Mitsunobu chemistry have appeared. Investigations of the reactions between a range of triarylphosphines and 1,1'-(azodicarbony1)dipiperidine indicate the formation of both triarylphosphonium radical cations and a radical anion derived from the azoester, via electron-transfer from the phosphine to the diazo function.300 Mitsunobu reagent systems continue to develop, and to find new applications. Tributylphosphine-azodicarboxamide combinations are more effective than the familiar triphenylphosphine-DEAD reagent for the one-pot cyanation of primary and some secondary alcohols.301 The stabilised ylide, Me,P+CH-CN, has now been used as a proton-abstracting agent in a modified Mitsunobu synthesis of C-alkylated arylmethylphenyl s ~ l f o n e s . ~Mitsunobu '~ chemistry is increasingly being adapted to solid phase systems, having been used in the past year for the intermolecular N-alkylation of aliphatic a m i n e ~ , ~the ' ~ synthesis of polyamine~,~'~ carbon-carbon bond formation in the C-alkylation of benzylic alcohols,305the N-alkylation of sulfonamides and alkylation of phenols, imides and carboxylic the synthesis of carbamates,307 and for the synthesis of tetrahydropyrazine-2-0nes.~'~Further conventional applications of Mitsunobu reagents have also appeared, including the synthesis of carbonyl compounds from 1,2-di0ls,~'~a one-pot regioselective and stereospecific azidation of 1,2- and 1,3-diols using trimethyl~ilylazide,~''and in hetero~yclic,~"and natural product chemistry.312 A Mitsunobu procedure for the synthesis of thioglycosides from 1-thiosugars and a series of alcohols has been developed, involving a combination of trimethylphosphine and 1,l '-azodicarbonyldipiperidine, the advantage being that trimethylphosphine oxide is easily removed on aqueous ~ o r k - u pl 3. ~Mitsunobu procedures for the synthesis of nucleosides from 1-thio- and l-seleno-glycosides have also been reported.314 Interest in the Staudinger reaction of phosphines with azides has also continued, and a theoretical treatment has a ~ p e a r e d . ~The ' reaction of an ortho-azidobenzamide with triphenylphosphine or methyldiphenylphosphine has allowed the isolation of the intermediate phosphazides (188) as crystalline solids, which, on heating in toluene, collapse to form the related phosphazenes which then undergo intramolecular aza-Wittig reactions.316Related dipolar species, e.g. (189) and (190), have been isolated from the reactions of the zirconaphosphine system (182) with a z i d e ~ . Various ~'~ monophosphino-phosphazenes, e.g. (191), have been isolated from the reactions of 0-substituted vinylazides with 2-1,2-bis(diphenylphosphino) ethene.3'8 The related reaction of a ferrocenylbisazide with 1,2bis(diphenylphosphin0) ethane has given the macrocyclic system (192).319 Monophosphino-phosphazenes have attracted the interest of the coordination
I : Phosphines and Phosphonium Salts
Ph3P + -Ph E-I -I
d:+J \
27
Me
N I -
kN I+
Ph2PR (187)
(188) R = Me or Ph
chemists and work in this area has been reviewed.320 The reactions of a z i d ~ t r i a z i n e sand ~ ~ ~tria~idopyridines~~~ with phosphines have also been explored. Staudinger reactions of acetylated glycopyranosylidene 1,l-diazides have given resonance-stabilised iminophosphoranes of 1 , 2 , 3 - t r i a ~ o l e Pro.~~~ tected glycosyl azides have been shown to react with acyl chlorides in the presence of triphenylphosphine to give glycosylamides in high yield at room temperature.324A simple route to carbamates is afforded by the reactions of trimethylphosphine with azides in THF at room temperature, followed by treatment with a chloroformate ester, work-up again being aided by the waterN-sulfonyltriphenylphosphinimines solubility of trimethylphosphine have been obtained by the reaction of triphenylphosphine under nitreneforming conditions with an N-sulfonyl iodonium imine.326 1.2.4 Miscellaneous Reactions of Phosphines. Procedures for the resolution of benzylcyclohexylphenylphosphine have been developed, involving adduct formation with cyclopalladated chiral amine complexes.3273328 A similar approach has also been used for the resolution of P-chiral secondary phosphines, e.g. (193).329Treatment of t-butyl(di-o-toly1)phosphinewith potassium tetrachloropalladate(I1) yields a cyclopalladated complex (194), involving chiral phos-
(1 93) R = CH2Ph or Me
28
Organophosphorus Chemistry
phorus, which was subsequently resolved.330The absolute configuration of the previously resolved chiral phosphine (195) has been determined by an X-ray study of the related borane complex.33' Phosphine radical cations have been generated via reactions of phosphines with the methylviologen dication, and their reactions with alkylpyridines A study of the thermal decomposition of cyclohexylphosphine has been reported.333 An example of the arylation of an unsymmetrical secondary phosphine has been reported, which involves treatment of a borane adduct of the secondary phosphine with copper(I), followed by an iodoarene in the presence of a palladium(I1) phosphine complex, providing a route to the borane adduct of a chiral tertiary p h o ~ p h i n eA . ~further ~ ~ example has appeared of the use of the o-diphenylphosphinobenzoate unit as a catalyst-directing structural unit for the stereoselective hydroformylation of chiral substrates.335 Photolysis of tetraphenylbisphosphine provides an initiator system for the bulk polymerisation of styrene and methyl m e t h a ~ r y l a t e . ~Fluoroalkylcopolymer-supported ~~ arylphosphines, useful in fluorous biphase catalysis, have been obtained via the copolymerisation of p-diphenylphosphinostyrene (196) and a fluoroalkyl acrylate ester.337 The first high molecular weight poly(phosphinoborane) (197), an 'inorganic' analogue of polystyrene, has been obtained from the borane adduct of phenylphosphine by rhodium-catalysed thermal d e h y d r o ~ o u p l i n g . The ~~~ aminoalkyl silylferrocenyldiphosphine (1 98) has been linked via the amino
r
PPh2
r
group to a cyclophosphazene core, forming a core dendrimer system with the chiral diphosphine units at the surface.339The cyclopolyphosphine (199) has been shown to undergo electron impact-induced fragmentation to form the neutral species P6, claimed as a new allotropic form of phosphorus.340 The diphosphinoketenimine (200) undergoes a reversible dimerisation on crystallisation at room temperature to form the dipolar system (201) by a novel [2+3] cycloaddition reaction.341 Photolysis of triarylphosphines in the presence of 9,lO-dicyanoanthracene in aqueous acetonitrile results in the formation of the
/s
P/p\P
\
/
CP* /p-p\cp*
pb=
h2
Ph2P
C NPh
Ph ,Ph Ph2PH'p+x Ph2P
pph2
Fh
NPh
I : Phosphines and Phosphonium Salts
29
related phosphine oxides via initial formation of the phosphine radical cation which then suffers nucleophilic attack by water to give an intermediate hydroxyphosphoranyl Triphenylphosphine has been shown to promote the cyclisation of 2-nitrophenylethenylketones to 2 - a ~ y l i n d o l e s . ~ ~ ~ Trichlorosilyldialkylphosphineshave been obtained by treatment of the related trimethylsilylphosphines with hexachl~rodisilane.~~ Tri-t-butylphosphine combined with caesium fluoride has been shown to facilitate carbon<arbon cross-linking of chloroarenes in the Stille reaction.345Aminolysis of a chromium carbene complex using the aminoalkylphosphine (202), followed by conventional N-methylation, has given the chiral chelate aminoalkylphosphine-carbene complex (203), the first of its type.346 The chemistry of phosphinocarbene systems has also developed significantly. The area has been reviewed.347Stable versions of transient push-pull phosphinocarbenes have been prepared, extending lifetimes from nanoseconds to weeks. Thus, e.g. the system (204) has been characterised by X-ray crystallography. Simpler systems, e.g. (205), have also been prepared, and are stable for a few days at - 30 "C in solution, but evaporation of the solution (even at - 50 "C) results in the formation of the dimers (206). The free phosphinocarbenes can be trapped by cycloaddition reactions with alkenes, to give phosphinocyclopropanes (207).348Another group of stable phosphinocarbenes are the silylated systems (208), which have been shown to act as electrophiles, reflecting the relatively
H2N
Ph
7
F3cp
R2P, C
PPh2
..
Ph
CF3 (204) R = Cy2N
R2px F3C
cF3 PR2
poor intramolecular donation from phosphorus into the vacant 2 orbital on carbon. With phosphine nucleophiles, the ylides (209) r e s u p The phosphinosilylcarbenes can also be trapped with electron-withdrawing a l k e n e ~ . ~The ~ ' electronic properties of diphosphinocarbenes (2 10) have received a theoretical study, which again confirms the relatively poor ndonor properties of p h o s p h ~ r u s . ~The ~ ' chemistry of the diradical species (211) has also been explored. On photolysis, it is converted into the previously unknown bicyclic system (2 12) which undergoes thermal conversion into a 1,4-dipho~phabutadiene.~~~ Treatment of (21 1) with a base generates the diradical carbene salt (213),a unique species.353A clean means of generating the ylide Ph3P=CI2 is afforded by the trapping of diiodocarbene (from iodoform and potassium t-butoxide) with triphenylph~sphine.~~~
30
Organophosphorus Chemistry R2P,
..C
,SiMe3
(208) R = Cy2N
x"' pY
Ar -
H
-Ar
(211) Ar = 2,4,6-But3C6H2
(208) R' = Cy2N R2 = Me or Ph
(2 10)
SiMe3 Ar-P#P-
-Ar
Ar
-pv .. P-Ar
,.
1
K e 3
H (212)
(213)
Interest has continued in assessing the stereoelectronic properties of phosphines used as ligands in homogeneous catalyst systems and metal complexes in and a review of this area has appeared.357 The catalytic applications of pyridylphosphine and related heteroarylphosphines have also been reviewed.358 Intramolecular and supramolecular phenylphenyl interactions have now been explored for metal complexes of triphenylphosphine, and, as for other triphenylphosphorus systems, sixfold phenyl 'embraces' are frequently found in the solid state.359 Some interesting reactions of phosphines in the coordination sphere of metal ions have also been reported. Trans- 1,2-bis(diphenylphosphino)ethene undergoes photolytic dimerisation only in the presence of nickel, palladium or platinum acceptors to form the related complexes of the tetra kis(dipheny lpho sphino)cy clobutane (214).360 The perfluoroaryldiphosphine (2 15) undergoes regioselective C-F
bond replacement reactions on heating with a cyclopentadienylrhodium complex.361The reactivity of copper(1) complexes of vinylphosphines has been studied. The coordinated phosphines do not undergo hydroboration, but can be polymerised under Lewis acid conditions.362 A selective decomplexation procedure has enabled the characterisation by NiMR in solution of the first free 7h3-phosphanorbornadiene (216), liberated from its tungsten pentacarbonyl complex by stepwise treatment with iodine, followed by imidazole. It has not been possible to isolate the free phosphine since, at
1: Phosphines and Phosphonium Salts
31
room temperature, it is found to eliminate phenylphosphinidene and form a 5-meta~yclophane.~~~ The mechanism of the 2-vinylphosphirane (2 17)-+ 3phospholene (2 18) rearrangement has been studied using metal-complexed systems. A biradicaloid transition state is implied in the reactions of the tungsten complexes, but the mechanism shifts towards a concerted process in the presence of copper(^).^^^ Ring-chain rearrangements of triphosphirane have been studied from a theoretical ~ t a n d p o i n t . ~ ~ ’ 2
Phosphine Oxides
2.1 Preparation. - Supercritical nitrous oxide has been shown to oxidise phosphines to the related phosphine oxides under mild conditions, allowing a simple isolation of products.366 Oxidation of precursor phosphines by hydrogen peroxide is the final step in the synthesis of the chiral functionalised phosphine oxides (219)367and A novel resolution procedure for the preparation of P-stereogenic phosphine oxides is afforded by the reactions of racemic chiral tertiary phosphines with an optically pure camphorsulfonyl azide, followed by separation of the diastereoisomeric phosphazenes, and acid hydrolysis to liberate the resolved, chiral phosphine oxides.369 Protected primary phosphine oxides (221) have been obtained by treatment of (diethoxyPh
(221) R’ = H or Me R2 = Me, Bu
alky1)-phosphinates with Grignard or organolithium reagents. Subsequent metallation and alkylation at phosphorus affords the protected secondary phosphine oxides (222), from which chiral systems, e.g. (223), have been obtained.370 Among new phosphine oxides prepared by the reactions of organolithium or Grignard reagents with phosphinyl halides are the organometallic system (224),371the unsaturated system (225),372(which, in the presence of a cobalt carbonyl complex, undergoes intramolecular cycloaddition reactions to form (226)), and the alkadienylphosphine oxides (227).373 Phosphine oxides have also been prepared by treatment of diphenylphosphinyl chloride with organocerium reagents.374 Phosphine oxides metallated at carbon adjacent to phosphorus have been used in the synthesis of functionalised systems, including 2-hydroxy-2-arylethyldiphenylphosphineoxides (228) the diphenylphosphinyl(resolved via chromatography on a chiral enamide (229),376 and a series of unsymmetrical bis(phosphiny1)methanes (230).377The silylated allylphosphine oxide system (231) has been obtained via an Arbuzov reaction of methyl diphenylphosphinite with an allylic chloride
Organophosphorus Chemistry
32
0 II
4 3 /
R' I
(223) R = alkyl or aryl
(222) R3 = alkyl
~H
PPh2
R3 RI R ~ C =c' C ' =CH -PR;
PR2 COCP
CI/
II
0
(227) R'-R4 = alkyl
0 Ar I1 / Ph2P-CH2-CH OH
0
0 NLi II Ph2P-CHrC 'But
0 II
II
R:PYPR: k3
(230) R' = Ph or But R~ = H or Pr" R3 = Me, Bunor Ph
(229)
precursor.378 Calixarenes bearing phosphine oxide substituents have been prepared, and their ability to act as selective complexing agents for rare earth metals Classical and phase transfer-catalysed Williamson reactions have been used to prepare (po1y)alkoxymethylphosphine oxides from (po1y)hydroxymethyl- or (po1y)chloromethyl-phosphine oxides.38' The reactions of the ylide derived from the 1,l-diphenylphospholanium cation with a,0-unsaturated thioesters provides a route to a series of cycloheptenylphosphine oxides, (232).382Aminoalkylphosphine oxides, e.g. (233), have been obtained from the addition of secondary phosphine oxides to i m i n e ~ . ~ ' ~ Routes to phenylbis(0-oxocyc1opentyl)phosphine chalcogenides (234) have been developed from the reactions of phenyldichlorophosphine with 1-mor-
(232) R = alkyl or aryl
0 Ph2:
(233)
0
0
@)2
(234)
(235) R = t-CeH17 ,3,3-tetramethylbutyI or 1,I
33
1: Phosphines and Phosphonium Salts
pholino~yclopentene.~~~ Optically pure bis(phosphine oxides) (235) have been prepared by a Kolbe electrolytic coupling reaction of carboxylic acids bearing Interest has also continued in the synthesis of a chiral phosphinoyl the fire-retardant polymeric phosphine o ~ i d e s . ~ ’ ” ~ ~ ’ 2.2 Reactions. - Asymmetric hydrogenation of the bis(phosphinoy1)butadiene (236) using a chiral ruthenium catalyst has given the chiral bis(phosphine A novel access to oxide) (237), the immediate precursor of (S,S)-chiraph~s.~’~ alicyclic phosphine oxides is provided by rhodium-promoted ring-closing metathesis of the bis-unsaturated phosphine oxides (238), giving, e.g. (239).390 Further studies of the influence of bulky substituents at phosphorus on the reactivity of cyclic phosphine oxides have appeared. The presence of the 2,4,6tri(isopropy1)phenyl group at phosphorus in 3-phospholene oxides (240)
(236)
(237)
(238) n, m = 1 or 2
(239)
(240)
enables stereoselective cyclopropanation at the double bond to be achieved, the outcome depending on conditions. The bulky group also influences the stereochemical and regiochemical course of the subsequent ring-enlargement reactions undergone by the cyclopropano-fused systems, e.g. (241).391Such bulky substituents at phosphorus also promote unexpected [2+2]cycloaddition reactions involving the P=O bond of five- and six-membered heterocyclic phosphine oxides, forming oxaphosphetes involving pentacovalent phosphorus, e.g. (242), on treatment with dimethyl acetylenedicarboxylate.3g2~3g3 Treatment of the cyclic phosphine oxides (243) with maleic anhydride or Nphenylmaleimide results in Diels-Alder addition to form the new 2-phosphabicyclo[2,2,2]octene-2-oxides(244). X-ray studies show that these systems have a less strained framework than previously described phosphabicyclooctadienes. Consistent with this, the bicyclooctenes require more forcing thermal decomposition conditions to split out the 03-h5species (245), which can be subse-
(241)
(242)
(243) R’, R2 = H or Me
(244) X = 0 or NPh
(245)
quently trapped using h y d r o q ~ i n o n e In . ~ ~related ~ work, photolysis of the bicyclooctenes in the presence of primary or secondary amines has given phosphinamidates, again suggesting involvement of the intermediate (245).395
34
Organophosphorus Chemistry
Photolysis of (244) in the presence of alcohols likewise results in the formation of esters of methyl(pheny1)phosphinic acid. However, *O-isotopic labelling studies provide evidence of, at least, the partial involvement of a pentacovalent phosphorus intermediate in this reaction, and so the previous assumption of the intermediacy of (245) may not be the whole story.396The phosphole oxide dimers (246) have been shown to undergo regioselective reduction and complexation on treatment with the dimethylsulfide-borane adduct, to form the bicyclic system (247).397Treatment of the propadienylphosphine oxide
(246) R', R2 = H or Me
(247)
Ar = Ph, Mes or 2,4,6-But3C6H2
(248) with the phosphinylhydrazine (249) results in the formation of the phydrazonophosphine oxide (250), which has subsequently been transformed into the 3-phosphinylated- 1-aminopyrrole system (25 1).398Thermal decomposition in refluxing toluene of the azidovinylphosphine oxide (252) results in the formation of the 2H-azirinylphosphine oxide (253). This system can also be
= * iPh21,p 0 PPhT II II 0
-
+
Ph2P-NHNHp
I
PPh2
I1
0
N"
a
II PPh2
0
obtained by treatment of propadienylphosphine oxides (248) with hydroxylamine, followed by tosylation and base-promoted cyclisation. Borohydride reduction of the azirine system yields the related aziridines, subsequently isolated in chiral form.399 Treatment of the phosphine oxide (254) with Grignard or organolithium reagents results largely in displacement of the methoxymethyl group to form the phosphine oxides (255). In most cases, traces of other phosphine oxides arising from displacement of a phenyl anion were also dete~ted.~"Side-chain elaboration of alkyl- or vinyl-diphenylphos-
35
1 : Phosphines and Phosphonium Salts 0
0
II
II
Ph2PCH20Me (254)
Ph2PR (255) R = alkyl or aryl
phine oxides continues to be exploited by Warren's group, with particular reference to controlling stereochemistry at remote sites by the diphenylphosphinoyl This group has also demonstrated diastereoselective nucleophilic addition of cuprate and chiral amide reagents to vinylphosphine oxide^.^" Side-chain elaboration of bromoalkyl- and vinyl-diphenylphosphine oxides with monoaza-15-crown-5 has given a new type of hybrid donor lariat crown ether system, e.g. (256).406A series of N-substituted carbamoyl- or thiocarbamoyl-methylphosphine oxides (257) has been obtained via the reactions of aminomethyldimethylphosphine oxide with alkyl-isocyanates and -isothiocyanates, re~pectively.~'~ Photolysis of a range of substituted benzyldiphenylphosphine oxides has shown that the diphenylphosphinoyl and benzylic radicals are the primary photopr~ducts.~'~ Interest in hydrogen-bonded adducts of phosphine oxides has also continued. Complexes of triphenylphosphine oxide with 4-amin0-4'-nitrobiphenyl~'~ and triphenylmethan~l~~' have been characterised. Phosphonyl-hydroxyl hydrogen-bonding has also found application in promoting the miscibility of polymer blends.41 Hydrogen-bond formation is also central to a new procedure for resolution of the secondary phosphine oxide (258), using a chiral binaphthalenediol or (S)-mandelic acid. The resolved phosphine oxides were then converted into the corresponding enantiopure hydroxymethyl(phenyl)(t-buty1)phosphine oxide via treatment with f ~ r m a l d e h y d e .The ~ ' ~ trifunctional triarylphosphine oxide (259) has been used as a component triacid to form 2D-networks with various metal ionbipyridyl complexes.413 Relatively few papers have appeared describing the reactivity of phosphine sulfides and selenides. The P-aryl phosphetan sulfide (260) undergoes photolysis at 254 nm to form a variety of products, which are assumed to arise from low coordination p,-bonded intermediates (261).414Three separate groups
II Ph2P-CH2 CH2-N
(256)
0 II BU'-P-H
0 X II II Me2PCH2NH- C -NHR
I
Ph
(257)X = 0 or S
(258) Ar-P=S
.OMe hv \
OMe
36
Organophosphorus Chemistry
have reported studies of charge-transfer adducts of phosphine sulfides and selenides with halogens and inter halogen^.^^ 5417
2.3 Structural and Physical Aspects. - X-ray crystal structures of tris-pchlorophenylphosphine oxide and tris-p-methoxyphenylphosphineoxide have been reported, which enable further understanding of the nature of the phosphorus-oxygen bond. Both structural data and IR stretching frequencies for these triarylphosphine oxides support the interpretation of the phosphorus-oxygen bond as having substantial multiple bond character, with a bond order between 1.7 and 1.8. The para-substituents have an insignificant effect on the nature of the phosphorus-oxygen bond.418Studies of the various conformational isomers of the phosphine oxides (262) and (263) have been reported for both the crystalline state and in solution in solvents of different polarity.419 A theoretical study of anomeric effects in dithianephosphine oxides, e.g. (264), has also appeared.420X-ray absorption near-edge structure 0
dSL
II
::
0
CH2PPh2
0 I1 Ph-P-(CH,-C-OMe)
b(Phz
II
Ph2PCH2
(262)
CH2PPh2
(263)
(264)
(XANES) measurements of triorganophosphine chalcogenides have been reported and related to the effects of sub~tituents.~~' Triethylphosphine sulfide appears to offer some potential as a non-linear optical organic material, and a technique for growing it as bulk single crystals has been developed.422
2.4 Phosphine Chalcogenides as Ligands. - The complexation of lanthanide and actinide ions by phosphine oxide ligands remains an active area, and a theoretical assessment of the coordination of phosphine oxides (and phosphate esters) by trivalent lanthanide ions has appeared.423 Trivalent lanthanide complexes of the functionalised enol phosphine oxide (265), (and a related phosphonate), have been described.424Complexes of thorium(1v) with bis(diphenylphosphino) ethane dioxide and bis(diphenylphosphinoy1)amide have also been ~ h a r a c t e r i s e d .Calixarene ~~~ systems which bear phosphine oxide
2
1: Phosphines and Phosphonium Salts
37
functionalities at either the narrow or the wide rim, e.g. (266),426have been shown to be excellent extractants for trivalent lanthanide and actinide ions426,427 and also to bind alkali metal ions selectively.428Triphenylphosphine oxide coordinates to metal ions at the centre of metallophthalocyaninate complexes when the latter are dissolved in the molten phosphine oxide at 300 0C.429Long chain alkylphosphine oxides have found use as complexing agents for phase-transfer catalyst systems involving molybdenum-peroxo complexes.430Trioctylphosphine oxide has been used for the solvent extraction of chromium(Ir1) corn pound^.^^' The ability of the heterocyclic system (267) to complex metal ions has also been A series of new chiral titanium alkoxide-o-hydroxyarylphosphineoxide complexes has found use as catalysts in the asymmetric trimethylsilylcyanation of aromatic aldehydes.433Manganese@) complexes of the nitronyl-nitroxide-functionalisedphosphine oxide (268) have been characterised, these systems exhibiting both ferro- and antiferro-magnetic interactions in the solid state.434 Ph
Ph
Tributylphosphine sulfide has been used as a co-catalyst with dicobalt octacarbonyl for the Pawson-Khand reaction.435Thermolysis of a mixture of cadmium chloride and trioctylphosphine sulfide at 250°C has been used as a route to the formation of nanocrystalline cadmium A complex of triphenylphosphine sulfide with a silver-tungsten-iodine acceptor has been characterised by X-ray Ferrocenylphosphine chalcogenides have attracted considerable interest as ligands. Complexes of the monophosphinophosphine sulfide (269) with rhodium have been ~ h a r a c t e r i s e dThe . ~ ~ disulfide ~ (270) forms complexes with both gold(1) and gold(m) acceptors,439and a silver(1) complex of the diselenide (27 1) has been preparedeU0 S
Se (&P I h2
e
P
p
h
@PPh2
2 I
ie
Fe II
Fe
@PPh2 II
S
(270)
&PPh2
II
Se
Organophosphorus Chemistry
38
3
Phosphonium Salts
3.1 Preparation. - Quaternization of triphenylphosphine with a wide range of haloalkanes in various solvents has been achieved in only four minutes under sealed tube conditions with microwave heating, compared to reaction times of several hours under conventional heating.441Conventional quaternization procedures have been used in the synthesis of further examples of benzylic triphenylphosphonium-end-stopperrotaxane systems,442the tetrakisphosphoniobenzyl-substituted porphyrins (272)443and the salt (273).444The reactions of tertiary phosphines with alkylthio(chloro)acetylenes, RSC = CCl, have given the salts (274) as initial The phosphonioalkylphosphonates (275) have been prepared as analogues of the related trialkylammonio systems, well-known cationic phospholipid substances used for DNA transfection, and found to be more efficient transfection reagents and also to be less toxic than the ammonium salts.447The reaction of tetraphenyldiphosphine with pyridinium hydrochloride has given the diprotonated species (276)
+ Ph3PCF2Br Br(273)
+ R3P-CECSR
CI -
(274) R = Ph, CH=CHPh or CH2CH2Ph
(272) R = Ph or Bu
0
(275) R’ = alkyl
+ + Ph2 P-P Ph2 H H
2CI -
(276)
R2 = C14-18alkyl
as a pyridine-resistant colourless solid.448Various approaches to the synthesis of phosphonium-functionalised polymers have been described.4493450 Full details have appeared of the synthesis of arylphosphonium salts bearing acidic functional groups on the aryl substituent, e.g. (277), these promoting watersolubility and aiding the separation of related phosphine oxides from Wittig procedures.451The Horner nickel(I1)-catalysed formation of arylphosphonium salts from aryl halides and tertiary phosphines has been employed in the synthesis of a series of calix[4]resorcinolarenes bearing arylphosphonio substituents (278) on the lower rim,452 the phosphonioaryltosylimino betaine (279),453and the ‘push-pull’ systems (280) and (281), from which the phosphine oxides (282) have been obtained by alkaline hydrolysis.454The betaine
I: Phosphines and Phosphonium Salts
39 R
(278) R = Me or C6HI3
(277)
(279)
Br&6Ph3
Br-
Me2N
Ar (280) Ar = P-bh?zNC& ferrocenyl or 2-thienvl
(282) Ar = P-MezNC6H4 pMe2NC6H4CH=CH-, ferrocenyl or 2-thienyl
(279) and the salts (280) exhibit a modest degree of negative solvatochromism, whereas the related phosphine oxides show a small positive solvatochromic effect. Arylphosphonium salts, e.g. (283),455have also been formed in the reactions of phosphine-coordinated arylpalladium(I1) Phosphonium salts have been obtained from the reactions of phosphines with iodonium salts.457459Thus, e.g. treatment of diphenyliodonium triflate with 1fluorovinyldiphenylphosphine has given the salt (284),458and the salts (285) have been obtained from the reactions of alkenyl(pheny1)iodonium tetrafluoroborates with triphenylphosphine in the presence of ethyldiisopropylamine. The latter reaction is believed to involve the trapping of a vinylcarbene by the p h o ~ p h i n e Carbene . ~ ~ ~ intermediates also seem to be implicated in the formation of difluoromethylphosphonium salts in the reactions of phosphines with tris(trifluoromethy1)bismuth and aluminium chloride in a~etonitrile.~~' Electrochemical oxidation of tertiary phosphines in the presence of alkenes leads to the formation of phosphonium salts via the intermediacy of phosphine radical cations.461 Perhaps the structural surprise of the year is the tetrazirconacenylphosphonium salt (286), shown to have a pZanar tetracoordinate phosphorus atom, prepared from the Schwarz reagent [Cp2Zr(H)Cl] and a triphosphenium salt.463Not surprisingly, this has raised a number of issues, t462
t
+pph3 F
N=CHPh
OTfBFq-
40
Organophosphorus Chemistry
provoking comment.464A range of new iodophosphonium salts has been prepared from the reactions of diisopropyliodophosphine with alkyl halides.465 The structural dependence of iodophosphonium cations on the nature of the associated anion has been the subject of a review.466Interest in the synthesis of phosphonium salts involving unusual anions has also continued. A tetraphenylphosphonium salt containing a complex rhenium anion has been shown to undergo metallation by the anion at the m- and p-positions of the phenyl rings of the cation.467The first phosphonium salt bearing a calix[4]arene unit as the anion has been prepared.468A phosphonium salt containing a sulfide-functional dicarbaborane anion has been structurally ~ h a r a c t e r i s e dTetraphe.~~~ nylphosphonium thiocyanate has also been the subject of an X-ray The reaction of tetraphenylphosphonium azide with azidotrimethylsilane in the presence of water or ethanol results in the formation of the non-explosive salt Ph4P'[N3HN3]-, containing the hydrogen diazide anion, which has also been structurally ~haracterised.~~' Various benzyltriphenylphosphonium salts involving oxidising anions, e.g. peroxym~nosulfate,~~~ p e r o x ~ d i s u l f a t eand ~~~ d i ~ h r o m a t ehave , ~ ~been ~ ~ prepared ~~~ and used as selective oxidising agents in synthesis. Methyltriphenylphosphonium dichromate has also been prepared. An X-ray study shows that the dichromate anion modifies the usual crystal packing of the cations, resulting in a layer-type lattice with only weak phenylphenyl 'embrace' interactions.476In contrast, structural studies on a series of methyltriphenylphosphonium salts involving polyhalocuprate(I1) anions reveal that the attractive supramolecular multiple phenyl embraces influence the geometry of the anions.477Treatment of methyltriphenylphosphonium iodide with tellurium tetrachloride results in the formation of a bis(phosphonium) halotellurate, treatment of which with base yields related ylide complexes of tellurium tetrachloride, enabling a synthesis of di~inyltellurides.~~~ 3.2 Reactions. - The phosphonium salts (287) have been shown to undergo facile nucleophilic displacement of triphenylphosphine on treatment with a range of C , N and S-nucleophiles, giving a range of functional P-substituted silyl enol ethers.479The 4-phosphonio-oxazolones (288) undergo dephospho-
(287)n = 0 or 1
(288)
niation on treatment with hydrogen iodide in dichloromethane at room temperature, providing a route to N-acyl-a-aminoa~ids.~~~ Interest has continued in studies of the liquid crystalline and other properties of phosphonium salts bearing two or three long alkyl chain s u b s t i t ~ e n t sIndeed, . ~ ~ ~ the ~ ~ non~~ linear optical properties exhibited by the smectic phase formed by dimethyldi (long chain alky1)phosphonium salts have been attributed to non-centrosym-
1 :Phosphines and Phosphonium Salts
41
metry arising from a weak association of halide counterions with the phosphonium centre, an interaction not possible for the related tetra-alkylammonium salts.482Significant differences in self-organising ability between tetra-alkylammonium and -phosphonium salts, bearing one or two long alkyl chains, have been noted, and linked to comparative antimicrobial properties.483 Further developments in the chemistry of the t ribut ylphosphine-carbon disulfide adduct have been reported. Its reaction with alkynes furnishes ylide intermediates which, on treatment with aldehydes, provide a route to 2arylidene- or 2-alkylidene-1,3-dithiole~.~’~ The coordination chemistry of tertiary phosphinesarbon disulfide adducts and related dipolar compounds has been reviewed.485A semi-molten mixture of hexadecyltributylphosphonium bromide and potassium fluoride has been used to promote nucleophilic fluoride exchange with various organic halides.486Polymer-supported phosphonium salts have been used in conjunction with potassium fluoride to promote fluorination of 2,4-dinitrochlorobenzenes under solid-solid-liquid phase-transfer conditions.487 Kinetic and thermodynamic parameters have been obtained for the alkoxide decomposition of 3-bromopropyltriphenylphosphonium bromide in dioxane-ethanol mixtures.488Alkyl migrations have been observed in the alkaline hydrolysis of tributylstyrylphosphonium bromide, yielding dibutyl(1-butyl-2-phenylethy1)phosphineoxide (289) in addition to other products.489The ability of allylphosphonium salts to promote photochemically- and thermally-induced radical-promo ted cationic polymerisation reactions has been studied.490The carbonyl group of the phosphonioacetaldehyde system (290) has been shown to be strongly hydrated under aqueous conditions, leading to a low intrinsic reactivity of the aldehyde f ~ n c t i o n a l i t y Nevertheless, .~~~ such salts have been shown to undergo imine formation on treatment with primary aromatic amines, the imines subsequently tautomerising to form the salts (291).492The occurrence of ‘six-fold’ 0 II
Bu~P-CH-CH~P~ I
Bu (289)
Ph3kH2CHO
+
Ph3P-CH=CH-NHAr
X-
X(290)
(291)
multiple phenyl ‘embraces’ in the solid state of a wide range of triphenylphosphonio-systems, including triphenylphosphine-group 13 adducts, has been studied.493Interest has continued in the study of coordinative peri-interactions systems. Structural studies of a in 1-dimethylamino-8-phosphonionaphthalene range of new amino-phosphonionaphthalene systems, e.g. (292), reveal short N-P distances, implying the existence of a strong coordinative interaction between nitrogen and the phosphonium centre.494In contrast, Schiemenz and co-workers have argued that the short N-P distances in such peri-naphthalene systems arise naturally as a result of the structural constraints imposed by the 1,8-disubstituted naphthalene unit, and that just because the observed N-P distances are shorter than the sum of the Van der Waals radii, it does not necessarily follow that there is a hypervalent coordinative interaction, either in
42
Organophosphorus Chemistry
the phosphonium salts or in related 1-amino-8-naphthylphosphines. There is little support from 'H- and 31P-NMRdata for the existence of such interact i o n ~The . ~ previously ~~ reported X-ray study of the phosphine (293) (Corriu et al., Angew. Chem., Int. Ed. Engl., 1993, 32, 1430), has been revisited, and is now thought to be that of the phosphine hydrobromide salt (294). The authentic phosphine (293) has now been prepared, the key step being treatment of the crude product with alkali. Structural data for the authentic phosphine (293) are different to those of the Corriu material.496 +
(294)
4
p,-Bonded Phosphorus Compounds
A review of lone pair effects involving multiple bonds between heavier main group elements contains much of relevance to p,-bonded phosphorus systems.497The diphosphene (295) has been shown to undergo cycloaddition reactions with isocyanides, to give the iminodiphosphiranes (296).498 A thirtyfive-fold excess of methyl triflate is needed to convert the diphosphene (297) to the salt (298), which is unstable in non-polar solvents. Experimental data show that the P=P bond becomes stronger on alkylation as is the case for N=N compounds.499 (MeSi)&,
(MeSi)3C, P=P
/ C(SiMe&
7 NxR
(296) R = CH2CN or CH2CF3
(295) Mes*, P=P \
, C(SiMe3)3
p=$
Mes*
(297) Mes* = 2,4,6-But3C6H2
Mes*
/
Mes* \
OTf-
Me
(298)
Cyclic triphosphenium ions, e.g. (299), have been obtained from the reactions of bis(dipheny1phosphino)alkenes with phosphorus trichloride in the presence of tin(I1) chloride in dichloromethane.sOO The simple phospha-alkene (300) has been formed and stabilised as a molybdenum complex.s01A range of new phospha-alkenes bearing bulky groups has been prepared, including (301),'02 the functionalised C-fluorophospha-alkenes (302),'03 and the phosphoranyl-functionalised system (303).504The polycyclic oxa-bridged system (304) has also been prepared, and shown to undergo addition reactions at the P=C bond with alcohols in the presence of a base.s0sThe reactions of sterically
I : Phosphines and Phosphonium Salts
43 Ar
Ar
(301)Ar = Mes, pMeOC6HI4 or p-tolyl
R3E-P
=C
F NEt2
(302)R3E = Me3Si, Me3Ge, (CF3)sGe or Me3Sn
(303)
protected phospha-alkenes with boron hydride reagents have been studied.506 A study of the reactivity of the carbonyl-functional phospha-alkenes (305) has also been reportede507The triphospha-Dewar-benzene (306) has been shown to undergo cycloaddition reactions with alkynes to form the triphosphabishomoprismane system (307).'08 Cycloaddition of t-butylphospha-ethyne to the phosphatriafulvene (308) results in the formation of a single isomer of the diphosphaisobenzene (309), having an allene system within the ring. This 0 II
R- C-P= C( NMe&
*But\
Ph
&+ P
0
(304)
(305)
P
(306)
%
compound undergoes cycloaddition reactions with trimethylbenzonitrile oxide at the P=C bond to form the fused system (310) in which the internal allene unit is still intact.509Radical anions of various isomers of phenylene bis(phospha-alkenes) e.g. (311), and other systems, e.g. (312) and (313), have been generated by electrochemical and chemical reductions and studied by EPR techniques.510The reactivity of the bis(phospha-alkene) (3 14) towards alkyllithium reagents and lithium aluminum hydride has been explored.511Oxida-
44
Organophosphorus Chemistry
(310)
Ar-P H
.
;
(31 1) Ar = 2,4,6-But3C6H2
-
A
r
Ar-P
P-Ar
tive addition of water or methanol to the diphosphacyclobutadiene ligand in a series of cyclopentadienylmolydenum complexes has been observed.512Electrochemical reduction of the diphospha-allene (315) yields a radical anion which, on protonation, gives rise to the 1,3-diphospha-allyl radical (316), characH I
Ar-P=C=P-Ar
ArP