Organophosphorus Chemistry / Edition 1 available in Hardcover
Organophosphorus Chemistry provides a comprehensive annual review of the literature. Coverage includes phosphines and their chalcogenides, phosphonium salts, low coordination number phosphorus compounds, penta- and hexa-coordinated compounds, tervalent phosphorus acids, nucleotides and nucleic acids, ylides and related compounds, and phosphazenes. The series will be of value to research workers in universities, government and industrial research organisations, whose work involves the use of organophosphorus compounds. It provides a concise but comprehensive survey of a vast field of study with a wide variety of applications, enabling the reader to rapidly keep abreast of the latest developments in their specialist areas.
Specialist Periodical Reports provide systematic and detailed review coverage of progress in the major areas of chemical research. Written by experts in their specialist fields the series creates a unique service for the active research chemist, supplying regular critical in-depth accounts of progress in particular areas of chemistry.
About the Author
Professor David Allen is Emeritus professor of chemistry at the Sheffield Hallam University, UK. His main research interests are in phosphonium salts and related compounds. Current interests include the preparation of phosphonioalkyl derivatives of biologically active molecules, the phosphonioalkyl group facilitating the passage of the biologically active agent through cell membranes, and studies of the formation of biologically active surface-functionalised gold nanoparticles.
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Organophosphorus Chemistry Volume 25
A Review of the Recent Literature Published Between July 1992 and June 1993
By D. W. Allen, B. J. Walker
The Royal Society of ChemistryCopyright © 1994 The Royal Society of Chemistry
All rights reserved.
Phosphines and Phosphonium Salts
BY D.W. ALLEN
1.1.1 From Halogenophosphines and Organometallic Reagents.- The use of organolithium reagents continues to dominate this route to tertiary phosphines. A range of 9-phosphinoanthracenes, e.g., (1), a red solid, isolated in only 7% yield, has been obtained from the reactions of 9-lithioanthracene with appropriate halogenophosphine reagents. The potentially atropisomeric system (2) has been prepared by the reaction of 2,2'-dilithio-1,1'-binaphthyl with organodichlorophosphines. However, n.m.r. studies reveal rapid interconversion of atropisomers in solution. Lithiation of a precursor bis(bromomethyl)binaphthyl, followed by treatment with chlorodiphenylphosphine, has proved to be the best route to the diphosphine (3). Double metallation of dibenzothiophen, using butyllithium in the presence of tetramethylethylenediamine, followed by treatment with chlorodiphenylphosphine, has given the isomeric diphosphines (4) and (5), separable by crystallisation. Further examples, (6), of phosphines bearing electroactive substituents have been prepared via direct metallation of the tetrathiafulvalene system. Direct metallation at the methyl carbon of hydrazones derived from t-butylmethylketone, followed by treatment with chlorodiphenylphosphine, affords a route to a range of new mixed donor ligand systems, e.g. (7). A similar strategy has been employed in the synthesis of the carbonyl-functionalised phosphine (8), from which a series of poly functional phosphinoimine ligand systems has been prepared. The phosphinocarbamates (9) have been obtained from the reactions of chlorodiphenylphosphine with the lithium enolates of various N,N-disubstituted acetamides. The 3-exo-isomer of the functionalised phosphine (10) is the initial product arising from direct lithiation of (1R)-(+)-camphor, followed by treatment with chlorodiphenylphosphine. However, on standing in THF solution, this undergoes conversion into the 3-endo isomer, subsequently isolated in 70% yield. Interest has continued in the synthesis of ferrocenylphosphines. The reaction of methyllithium with ferrocenyldichlorophosphine is the final stage of an improved route to ferrocenyldimethylphosphine (11), although difficulty is still being experienced with the synthesis of the dichlorophosphine intermediate. Organolithium-based routes to the ferrocenyldiphosphines (12) and (13) have been developed. Directed ortho-lithiation of ferrocenes bearing chiral sulphoxide or tertiary amine functionalities is the basis of routes to the chiral phosphines (14) and (15), the latter system having the additional feature of fluxionality derived from cyclopentadienyl substituents present at phosphorus. Both organolithium and Grignard routes have been employed in the synthesis of chiral phosphinoaryldihydro-oxazoles, e.g., (16). The reaction of 1,2-bis(dichlorophosphino)ethane with t-butylmagnesium bromide provides a good yield of the diphosphine (17), this procedure having considerable advantages over the use of t-butyllithium, which gives rise to a mixture of products. Ethynylmagnesium bromide has been used in the synthesis of the alkynylphosphine (18). Full details have now appeared of the conversion of the titanocycle (19) into the phosphetane system (20), isolated as a mixture of geometrical isomers. Attempts to form polymers via thermally-induced ring opening of the phosphetane met with only very limited success, indicating that the ring system is quite stable.
1.1.2 Preparation of Phosphines from Metallated Phosphines.- A simple route to alkali metal bis(trimethylsilyl)phosphide reagents is afforded by the reaction of tris(trimethylsilyl)phosphine with alkali metal alkoxides. A biproduct isolated in the preparation of lithium monomesitylphosphide has been shown to have an unusual (LiPLiC)2 structure involving an eight-membered ring. Nucleophilic attack by lithium diphenylphosphide on substrates bearing good leaving groups, commonly various sulphonate esters, has been employed in the synthesis of the chiral diphosphine (21), various polydentate phosphinoamines, e.g., (22), and phosphinoalkylphosphazenes, e.g., (23), which on hydrolysis yield the related phosphinoalkylamine. The axially dissymmetric and axially asymmetric ligand system (24) has been prepared via ring-opening of precursor dinaphthazepinium salts with lithium diphenylphosphide. The synthetic utility of the diphosphide (25) has been explored. As a result of the electrophilicity of the trimethylsilyl groups, this reagent is an effective source of the bis(dianion) (26). New chiral diphosphines, e.g., (27), have been prepared therefrom. Treatment of a dibromoferrocene with the diphosphide reagent (28) provides a route to the ferrocenophane (29). Monolithiation of cyclohexylphosphine, followed by treatment with aryldichlorosilanes, results in the formation of the triphosphatrisilacyclohexanes (30), which are found to have a novel coordination chemistry, acting as coronands via phosphorus coordination. Displacement of chlorine from 2-chloropyridine systems by lithium diphenylphosphide is the key step in the synthesis of the heteroarylphosphines (31) and (32). An X-ray study of lithium di(2-pyridyl)phosphide has revealed that the usual lithium-phosphorus interaction is not present, the lithium atom being involved in coordination with the pyridine nitrogens. Lithiophosphides (and occasionally other alkali metal phosphide reagents) have received wide application in the synthesis of organophosphino derivatives of boron, aluminium, gallium, and indium, and also of germanium and zirconium. Most of these compounds are found to have associated structures as a result of intermolecular coordinative interactions between phosphorus and the metalloid/metal present. However, a series of monomeric phosphinogallanes, e.g., (33), has been prepared, intermolecular coordinative association being prevented by the presence of bulky groups at both phosphorus and gallium. An X-ray study of (33) reveals a flattened pyramidal structure at phosphorus, perhaps indicating some degree of intramolecular phosphorus -> gallium π-interaction. Consistent with this, solution n.m.r. studies indicate a small, but significant barrier to rotation about the gallium-phosphorus bond.
Both lithium- and sodium-diphenylphosphide reagents have been employed in the synthesis of the new water soluble tertiary phosphines, (34) and (35). A range of tetraphosphines (36) has been prepared from the reactions of chlorodiorganophosphines with lithium-, sodium-, and potassium-bis(trimethylsilyl)phosphide reagents. Metallation of the bis(secondary) phosphine (37) with lithium, sodium, or potassium metal, followed by treatment of the resulting bis(metallophosphide) with a 2-halo(methoxy) benzene, has given the new chiral diphosphine ligand (38), the diastereoisomers of which have been separated via chromatography of their palladium complexes. Sodium diarylphosphide reagents have been employed in the synthesis of the tetraphosphine (39), and the new chiral ligands (40) and (41), the latter being derived from the commercially available L-valine as the chiral source. Diorganophosphide reagents generated by chemoselective cleavage of triarylphosphines using a sodium-potassium alloy in dioxan have been used in the synthesis of the chiral diphosphines (42). A tosylate-potassium diphenylphosphide route has been adopted for the preparation of the triphosphine (43). Alkylation of phosphide reagents derived from deprotonation of palladium complexes of the diphosphine (44) using potassium carbonate, has given a route to the macrocyclic tetraphosphine systems (45).
1.1.3 Preparation of Phosphines by Addition of P-H to Unsaturated Compounds.- A number of interesting examples of this route has appeared over the past year. In the presence of AIBN, the unsaturated primary phosphine (46) undergoes intramolecular cyclisation to form the bicyclic system (47). A new approach to the preparation of water-soluble phosphines is afforded by the addition of primary and secondary phosphines to mono-allyl ethers of ethylene glycol derivatives and of carbohydrates, giving, e.g., (48) and (49). Various polyphosphines, e.g., (50), have been obtained by addition of primary phosphines to 1,1-bis(diphenylphosphino)ethenes. Addition of primary and secondary phosphines to 2-(vinylthio)tetrahydropyrans gives phosphinoalkylhemithioacetals, e.g., (51), hydrolysis of which results in the formation of the related 2-mercaptoalkylphosphines. Free radical addition of diphenylphosphine to 1,6-diene or -enyne systems proceeds with cyclisation of radical intermediates. Thus, e.g., the diene (52) is converted into the phosphine (53). A related enyne system has given the unsaturated phosphine (54). The heterocyclic system (55) has been prepared by addition of phenylphosphine to an unsaturated ketone. Primary and secondary phosphines coordinated to transition metals have been added to alkynes, resulting in the formation of coordinated vinylphosphines, with trans-stereospecificity. Macrocyclic phosphines, (56), have been prepared by metal template-assisted addition of bis(secondary phosphines) to divinylphosphines. There have been further reports of the addition of secondary phosphines to alkenylsilanes. In a similar vein, phosphines linked to a metal alkoxide functionality via a spacer group, e.g., (57), have been obtained by addition of diphenylphosphine to the products of the reaction of acrylic acid with metal alkoxides. Examples of the addition of primary and secondary phosphines to isocyanato- and isothiocyanato-phosphoryl systems have been reported, and this reaction has been applied to the synthesis of heterocyclic systems. Thus, e.g., (58), is formed in the reaction of phenylphosphine with phenylphosphonyl di-isothiocyanate.
1.1.4 Preparation of Phosphines by Reduction.- A useful review of the various methods for the reduction of quinquevalent phosphorus to the trivalent state has appeared. Trichlorosilane, usually in conjunction with triethylamine, remains the reagent of choice for reduction of tertiary phosphine oxides. Among new chiral phosphines prepared in this way are 6-endo-hydroxynorphos (59), and the dissymmetric systems (60) and (61). The use of dichloroalane, "AlHCl2", in an ether solvent, enables the chemoselective reduction of vinylphosphinates to form the unstabilised secondary vinylphosphines (62).
1.1.5 Miscellaneous Methods of Preparing Phosphines.- A new route to tri-(2-pyridyl)-phosphine is provided by the reaction of pyridine with phosphine in the presence of copper(II) compounds. The functionalised tri-(2-furyl)phosphine (63) is formed in high yield in the reaction of furfural N,N-dimethylhydrazone (3 equivalents) with phosphorus tribromide in pyridine. The imidazopyridinophosphine (64) has been prepared in a similar manner by the reaction of the parent heterocyclic system with iododiphenylphosphine in benzene containing pyridine. Surprisingly, treatment of (64) with triethyloxonium tetrafluoroborate results in N-alkylation, whereas with iodomethane, alkylation at phosphorus occurs. Metallation of the thienylsilane (65) with butyllithium occurs specifically at the 2-position of each ring, and treatment of the trilithio derivative with triphenylphosphite has yielded the bicyclic system (66). The latter undergoes oxidation at phosphorus in the usual way, but fails to react with sulphur or selenium. The high s-character of the phosphorus lone pair is revealed by a 31P chemical shift of -92 ppm. A one-step preparation of the bis(phospholano)butane (67) is provided by the reaction of 1,4-dilithiobutane with trimethylphosphite. The perfluoroalkyl diphosphine (68) has been isolated in 15% yield from the reaction of 1,2-bis(dichlorophosphino)ethane with bromotrifluoromethane in the presence of tris(diethylamino)phosphine. This compound is extremely volatile, codistilling with dichloromethane. A series of phosphino(bipyridyl)ferrocenes, e.g., (69), has been prepared by the reaction of the related C-lithio(phosphino)ferrocenes with bipyridyls. The reactions of the phenol-functionalised phosphine (70) with the chiral chlorophosphite (71) in the presence of triethylamine have given a series of new, chiral phosphine ligands, e.g., (72), a tetraphosphorus ligand having C3-symmetry. In a similar vein, the base-promoted reactions of the thiophenol-functionalised phosphine (73) with various 1,3,5-tri(bromomethyl)benzenes under high dilution conditions have yielded a series of in-phosphaphanes, e.g., (74), of interest in connection with the study of possible charge-transfer interactions between phosphorus and the nitroarene basal unit.
Interest in the preparation of water-soluble phosphines continues. Improved routes to tris(hydroxymethyl)phosphine have been described, and a series of water-soluble transition metal complexes prepared therefrom. Sulphonation of tris(ω-phenylalkyl)phosphines has given a series of water-soluble ligands (75). Aqueous alkaline hydrolysis of the known diphosphinomaleic anhydride (76) provides a route to the water-soluble diphosphine (77). However, care is needed in the work-up in order to avoid oxidation at phosphorus and addition to the double-bond. The stereochemical course of the first step of a previously established route to chiral phosphines, involving nucleophilic attack on chiral oxazaphospholidine borane complexes with retention of configuration at phosphorus, has been established by X-ray studies. Oxidation of hydroxyalkylphosphine-borane complexes, followed by removal of the borane protecting group from phosphorus using triethylamine, has given a series of phosphines bearing aldehyde, ketone or carboxylic acid functionality, e.g., (78). Interest has also continued in the synthesis of systems in which there is the possibility of extended conjugation between a trivalent phosphorus donor center and an organoboron acceptor. A series of phosphino-organoboranes, (79)-(81), has been prepared. However, there is little evidence of π-conjugation in these systems. An unexpected regioselective synthesis of the 1,-diphosphinoethanes (82) is provided by hydrozirconation of vinylphosphines, followed by the addition of chlorodiphenylphosphine. Secondary alkylarylphosphines bearing both donor and acceptor substituents in the aromatic ring, have been prepared by palladium(O) complex-catalysed cross-coupling reactions of haloarenes with alkyl(trimethylsilyl)phosphines. A mixture of adamantylphosphines, (83) and (84), is formed in the reactions of 1-(2-haloethyl)adamantanes with the phosphine-aluminium chloride complex. Elaboration of other functional groups present in tertiary phosphines has been employed in the synthesis of a range of phosphino-imines (85), the chiral phosphinohydrazone (86), and the macrocyclic system (87). Various dioxaboranes bearing exocyclic phosphino substituents, e.g., (88), have been prepared.
Interest also continues in the chemistry of polyphosphines and a major review of the area has appeared. Baudler's group has described two new polyphosphines, P13Pri5 and P20Pri6, isolated from the reactions of isopropyldichlorophosphine with magnesium in the presence of white phosphorus. The reaction of white phosphorus with hexa(t-butyl)disilane has given "tris(supersilyl)heptaphosphane(3)", (89), and with tetraaryldisilenes, thebicyclic system (90) is formed.
1.2 Reactions of Phosphines
1.2.1 Nucleophilic Attack at Carbon. - The rates of the reactions of tertiary phosphines with chloroalkanes have been shown to be greatest in protic solvents of moderate acidity (pKa = 10-13). Mixtures of diastereoisomeric phophonium salts, e.g., (91), have been isolated from the reactions of the antibiotic bicyclomycin (and its derivatives) with tributylphosphine. Ring-opening of THF coordinated to zirconium halides occurs in the presence of phosphines, leading to the isolation of related complexes of the phosphonium betaines (92). Ring-opening of oxaziridines occurs on treatment with triphenylphosphine, with the formation of imines and triphenylphosphine oxide. Intermediates arising from nucleophilic attack at carbon by trialkylphosphines are implicated in a number of reactions catalysed by such compounds. Thus, e.g., trialkylphosphines catalyse the addition of alcohols to αβ-unsaturated alkynic acid esters, via nucleophilic attack by alkoxide ion on the intermediate vinylphosphonium salt (93), with displacement of the phosphine. In a similar vein, a catalytic amount of trialkylphosphine has been shown to catalyse the [3,3]-rearrangement of allylic acrylates, and the conversion of ynones to conjugated dienones is promoted by a catalytic quantity of triphenylphosphine. Tributylphosphine, a weak base but powerful nucleophile, has been shown to act as a remarkable acylation catalyst in the reactions of alcohols with acid anhydrides, its catalytic effect being comparable with that of 4-dimethylaminopyridine. When pure acetic anhydride is treated with tributylphosphine, the diphosphonium salt (94) is formed, and phosphonium intermediates have been detected spectroscopically in the above catalysed processes.
Excerpted from Organophosphorus Chemistry Volume 25 by D. W. Allen, B. J. Walker. Copyright © 1994 The Royal Society of Chemistry. Excerpted by permission of The Royal Society of Chemistry.
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Table of Contents
ContentsCHAPTER 1 Phosphines and Phosphonium Salts By D.W. Allen,
CHAPTER 2 Pentaco-ordinated and Hexaco-ordinated Compounds By C.D. Hall,
CHAPTER 3 Tervalent Phosphorus Acid Derivatives By O. Dahl,
CHAPTER 4 Quinquevalent Phosphorus Acids By R.S. Edmundson,
CHAPTER 5 Ylides and Related Compounds By B.J. Walker,
CHAPTER 6 Phosphazenes By C. W. Allen,
Author Index, 320,