Carbodiphosphoranes synthesis

Carbodiphosphoranes (bistriorgano)phosphoranylideneniethanes, hexaorganocarbodiphosphoranes) may be generated from suitable phosphonium salt precursors by dehydrohalogenation or dehalogena-tion. Since the first synthesis of hexaphenylcarbodiphosphorane, a series of symmetrical, unsymmetri-cal, mixed alkyl/phenyl, cyclic and difunctional carbodiphosphoranes have been prepared. Compounds synthesized until 1984 have been listed. 

Stepwise deprotonation of methylenebis(triorgano)phosphonium salts with bases yields carbodiphosphoranes via intermediate semi-ylide salts, which may also be accessible by alkylation or phosphinol-ation of corresponding alkylidenephosphoranes (equation 118). " It depends on the starting phosphonium salt and the base whether the intermediate ylide salts can be isolated or not. Suitable bases are sodium amide, alkali metal hydrides, alkylidenetrialkylphosphoranes, potassium and lithium orga-nyls. For the synthesis of hexaphenylcarbodiphosphorane improved methods have been reported by which this compound may be generate without isolation of the ylide salt and on a large scale. 

The number of theoretical investigations of transition metal complexes with carbodiphosphoranes and related divalent carbon(O) ligands is rather small. Quantum chemical calculations of the nickel complexes (CO) Ni-C(PPh3)2 with n = 2, 3 have been published together with experimental work which describes the synthesis and X-ray structure analyses of the compounds [107]. The first systematic... 

Persistent carbenes were introduced into synthetic chemistry by Bertrand, who isolated the first carbene Rj P-C-SiR 3 in 1988 [13], and by Arduengo [14], who synthesized the N-heterocyclic carbenes (NHCs) in 1991. Stable carbones were actually isolated much earlier than carbenes. In 1961, Ramirez et al. [15] reported on the synthesis of the compound hexaphenyl-carbodiphosphorane ClPPhjlj- The authors assumed that the molecule has a linear structure PhjP=C=PPh3, which they described with resonance structures in terms of double bonds between phosphorous and carbon and as a double ylide Ph3P=C=PPhj Phj P(-l-)-C(2—[-(-l-jPPhj. 

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