Genügend starke anionische Nucleophile X− bauen weißen Phosphor unter mehr oder weniger weitgehender Disproportionierung ab. Mit Kronenether‐Alkali‐, Ammonium‐ oder Phosphoniumcyaniden, X− = CN−, entsteht dabei selektiv das entsprechende Dicyanphosphid, P(CN)2−, und ein Polyphosphid, bevorzugt P15−.
[18] Krone‐6‐KP(CN)2 entsteht auch bei der Umsetzung von P(CN)3 mit KF und Kronenether. Im Kristall dieses Salzes sind die am Phosphor (um 95°) gewinkelten Dicyanphosphid‐Anionen mit beiden Stickstoffenden an je ein Kation koordiniert. Der PC‐Abstand ist (mit durch‐schnittlich 168 pm) so kurz wie in Phosphaalkenen. δ13C und JPC von P(CN)2− ordnen sich gut in einen für Cyanphosphorverbindungen allgemein geltenden Zusammenhang mit der Ladungsdichte am Phosphor ein.
A nice example for the stepwise transition from the polymeric solid to a solution in which solvated and separated ions predominate is provided by the Li3P7 system. In solvent‐free Li3P7, all the P atoms participate in the coordination of the Li atoms, and the Li atoms always belong to several P7 groups, whereas in [Li(tmeda)]3P7 the Li atoms are only coordinated by the twofold bonded P⊖ atoms of one P7‐group and by the solvent. The title complex can be regarded as a model for the species in solution. In this case the Li atoms would be of significance for the valence fluctuation in P.
Phenyl cyanophosphide PhPCN-is formed in the reactions of P(CN); with phenyllithium and of PhP(CN), with C N -, and it may best be prepared by nucleophilic degradation of (PhP), with ammonium or phosphonium cyanides. With sulfur it yields phenyl cyanodithiophosphinates 4, by alkylation alkyl(pheny1)cyanophosphanes 6 and by hydrolysis of the latter alkyl(pheny1)phosphine oxides 7. -The molecular structure of [Ph,PNPPh,]PhPCN (3c) as determined by X-ray analysis shows an almost planar anion with a 102" C P C angle. A long P C and short CN bond in the PCN group make PhPCN-appear as "cyanide complex of phenylphosphinidene".
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