Phosphorus anion stabilisation

There have been ab initio studies of the bonding for a series of imino and amino phosphorus molecules,15 and for the phosphonium ylides (8).14 The anion character of the ylidic carbon is intermediate between that of olefinic and substituted carbanions. Polarisation of the H3P group has a stabilising effect. The influence of the substituent X on the inversion of the carbanion and also the tendency of the molecule to dissociate to carbene and phosphine is also discussed.14 CNDO/S MO calculations on the... 

Related to these diphosphine dichalcogenides are the triphosphine trisulfides [R2P(S)]3CH (12) which can be prepared from lithiated methylene diphosphine disulfides upon treatment with thiophosphinic chlorides (Equation 9). Deprotonation of 12 with tBuLi gives a resonance-stabilised anion 13 containing a planar central carbanion whose charge is delocalised onto the three neighbouring phosphorus and sulfur atoms.32... 

Since the phosphate anion is resonance stabilised, nucleophilic substitution of the bromine atom of the coumarin derivative can occur by either of the two free oxygen atoms. Thus two diastereomers will be produced, which may be distinguished between merely by considering the configuration at the phosphorus atom. In a publication it was shown that using the tetrabutyl-ammonium salt of cyclic AMP (cAMP) in acetonitrile the diastereoisomeric ratio was 85 15 in favour of the compound with an S-configured phosphorus atom [10]. 

The lithiation of sulfoxides and sulfones gives stabilised species which are arguably not organolithiums but anions with O-Li bonds.74 76 Lithiation a to phosphorus likewise gives anions which are outside the scope of this book. 

Reports of nucleophilic attack at atoms other than those above have also appeared. A kinetic study has compared the effectiveness of tertiary phosphines and phosphite esters in the catalysis of the cleavage of the silicon-silicon bond of methylchlorodisilanes, providing evidence for the involvement of a stabilised silylene intermediate. The anion of the y-phosphino-p-diketimine (197) has been shown to react with arsenic trichloride to give the phosphino-arsino-p-diketimine (198), in which there is a coordinative link from phosphorus to arsenic. ... 

Wadsworth, W.S., Jr., Synthetic applications of phosphoryl-stabilised anions, Org. React., 25,73, 1977. Walker, B.J., Transformations via Phosphorus-Stabilised Anions. Part 2. PO-Activated Olefination, Academic Press, New York, 1979, p. 155. 

Overall levels of innovation in the area this year are disappointingly low. All the various forms of phosphorus-based olefination continue to be used widely in synthesis and perhaps the relative paucity of new phosphorus chemistry is a reflection on the extent to which these methods have been developed. One area which does continue to develop, and where there is still considerable potential, is the use of phosphorus stabilised anions in enantioselective and asymmetric synthesis. Warren s continuing use of phosphine oxides and Denmark s excellent contributions to this area are especially worthy of mention. 

Rotational barriers of the P-C bond in phosphoryl- and thiophosphoryl-stabilised carbanions have been studied by ab initio calculations on the 2-oxo-(and thioxo)-2-methyl-l,3,2-diazaphosphirane-(7) and -diazaphospholidine anions (8), at MP4(SDQ)/6 - 31+G //HF/6 - 31+G +ZPE levels. MNDO calculations have shown that 2-pyrrolinones cannot be phosphorylated with phosphorus nucleophiles. ... 

In methyl cyanide solution, phosphorus pentabromide is an electrolytic conductor like the pen-tachloride, with ion species PBr4+ and PBr ", the anion being on the limit of stability and stabilised by solvation. The tetrahedral PBr4+ ion, on the other hand, is relatively stable as indicated by the production of PBr4+ PFg" on fluoridation of PBrj in non-ionic solvents. Also known is PBr4 AsF ". 

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