Crown-6 Potassium Dicyanophosphide

Submitted by ALFRED SCHMIDPETER and GUNTHER BGRGET Cbedted by DON J. CHANDLERt and RICHARD A. JONESt 

The dicyanophosphide(l-) ion P(CN)2 may be viewed as a homolog of the dicyanoamide(l-) ion N(CN)2 and related to the thiocyanate ion SCN in the series of (pseudo)halide ions E(CN)7 n = group number of element E). In this sense it can be used in reactions with various kinds of electrophiles to introduce the P(CN)2 group. It may also be viewed as a cyanide complex of cyanophosphinidene PCN or of the phosphorus(I) cation P+, thus, strong nucleophiles replace one or both cyanide ions.  

The dicyanophosphide(l-) ion was first prepared by reduction of P(CN)3. It is more conveniently obtained from white phosphorus in a nucleophilic disproportionation by an ammonium, phosphonium, or crown ether alkali metal cyanide.  

Crystalline [([18]crown-6)K][P(CN)2] is the preferred material for further reactions. In the P4-disproportionation reaction, crown ether potassium polyphosphides are formed as the second product. Their composition and solubility depend on the stoichiometry used. The intense red color of the solution in early stages of the reaction is caused by an intermediate high concentration of soluble polyphosphides. The final equilibrium concentration of these phosphides can contaminate and color the isolated dicyanophosphide. To avoid this contamination, the remaining soluble polyphosphides are converted to insoluble ones by an excess of white phosphorus. 

A dry 250-mL, two-necked, round-bottomed flask with an inert-gas inlet is equipped with a magnetic stirring bar and a reflux condenser topped by a paraffin oil filled pressure relief valve. The reaction is performed under dry and oxygen-free argon.t Traces of oxygen are removed from the inert 

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