Phosphines tertiary, unsymmetrical

It is now well-established that unsymmetrical substituted menthylphosphinates, RR P(0)0Men, as well as the corresponding phosphine-boranes RR P(BH3)OMen and phosphinothioates RR P(S)OMen, can be separated readily into the di-astereomeric forms, and subsequently reacted with Grignard reagents to afford P-chirogenic tertiary phosphines with a high degree of stereospecificity [57]. The... 

Gusarova, N.K., Shaikhudinova, S.I., Reutskaya, A.M., Tartarinova, A.A., and Trofimov, B.A., One-step synthesis of unsymmetrical tertiary phosphine oxides from red phosphorus and organyl halides, Russ. Chem. Bull., 49, 1320, 2000. 

The 1,4-disilylation of a,/3-unsaturated ketones has been reported by Ito and co-workers.172 Unsymmetrically substituted disilanes, PhCl2SiSiMe3 and Cl3SiSiMe3, undergo reaction in the presence of catalytic amounts of palladium complexes with tertiary alkyl phosphine or bidentate phosphine ligands to yield /3-silyl ketones [Eq. (64)]. 

At about the time of Wilkinson s discovery, new schemes were developed by others for the preparation and configurational correlation of chiral phosphines (lOa-e). The combination of advances in homogeneous catalysis and chiral phosphine technology prompted research on chiral phosphine complexes. Horner et al. (11) were the first to hypothesize in print that rhodium complexes containing optically active tertiary phosphine ligands should effect the asymmetric hydrogenation of unsymmetrically substituted olefins. 

Unsymmetrical Tertiary Phosphines 1.12.2.5.1 Preparation by classic methods... 

For alkylation of phosphines containing C-H bonds their alkali salts are usually treated with alkyl halides. Thus primary and secondary phosphines can be obtained by metalation of phosphine itself with sodium in liquid ammonia and subsequent alkylation 208 phosphirane, which is unstable, is also prepared in this way, from sodium phosphide and ethylene dichloride.209 High yields of primary phosphines are afforded by alkylating lithium phosphide, which is formed almost quantitatively by metalating phosphine with butyl-lithium.210 Since the hydrogen can be replaced stepwise by metal, unsymmetrical secondary and tertiary phosphines can be built up from PH3 or a primary phosphine.211 Use of alkali phosphides is not limited to alkylation potassium diphenylphosphide reacts quantitatively with iodobenzene, yielding triphenyl-phosphine.212... 

Preparation of quaternary phosphonium salts is of great importance as it leads to the phosphorus ylides that are needed for Wittig olefination (see page 996). Further, quaternary phosphonium salts are intermediates in the methods of preparation of unsymmetrical phosphines that depend on successive alkylation of tertiary phosphines and degradation of the resulting quaternary salts. Three processes have been developed for the last-mentioned reaction ... 

White phosphorus reacts with Grignard reagents and organolithium compounds, generating phosphides which give phosphines on hydrolysis phenyl-lithium yields up to 40% of phenylphosphine in this way.361 Alkylation by alkyl halides before hydrolysis leads to unsymmetrical tertiary phosphines.215... 

Unsymmetrical tertiary phosphines can be synthesized from dichloro-358, 368,378 or chloro-phosphines358,379 and Grignard reagents. 

The organophosphides derived from phosphorus and organometallic compounds were found to react with alkyl halides in a manner typical of phosphides, to give unsymmetrical tertiary phosphines (6). Thus, phosphorus, plienyllithium, and butyl chloride gave dibutylphenyl-phosphinc and butyldiphenylphosphine in 37% and 44% yields, respectively. 

Substituted phosphonous halides condense rapidly with excess Grignard reagents to give good yields of unsymmetrical tertiary phosphines. The reaction is often exothermic and is conducted at low temperatures under nitrogen to avoid the formation of phosphine oxides. 

Comparison of experiments performed in tetrahydrofuran (14,164,184) versus ether (20,40) clearly demonstrates the former to be the superior solvent. Unsymmetrical phosphinous halides are not easily obtained but have been employed as precursors of totally unsymmetrical tertiary phosphines (40). In the case described, p-bromophenylphenylphos-phinous chloride (10) resulted from a high-temperature condensation of p-bromophenylphosphonous dichloride and diphenylmercury. Tertiary phosphines of the type RR R"P are important since elegant research... 

King et developed a route to poly(tertiary phosphines) by use of a base-catalyzed addition of a phosphorus-hydrogen bond to the carbon-carbon double bond of various vinylphosphine derivatives the first extensive series of methylated polyphosphines were prepared this way. The synthesis of unsymmetrical diphosphines of the type i 2PCH2CH2P(CH3)2 involves addition of a P-H bond to CH2=CHP(S)(CH3)2 via potassium tert-bwioxxdQ catalysis, followed by desulfurization with LiAlH4 in boiling dioxane (i.e.. Equations 10,11). 

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