Methods of distinguishing between cyano-stabilised imino- and methylene-phosphoranes. Crystal structures of adducts from triphenylphosphine and tetracyanoethylene (a heptacyanocyclopentenyliminophosphorane) and from triphenylphosphine and dicyanoacetylene (a hexacyanohexa-1,6-dienediphosphorane)

Abstract

Cyano-stabilised methylene- and imino-phosphoranes may be distinguished by the much faster rate of alkaline hydrolysis of the former and also by the position of the long-wavelength bands in their u.v. spectra, if the anion is delocalised over two or more multiple bonds. The adduct from triphenylphosphine and tetracyanoacetylene has been shown to be 2,3,3,4,4,5,5-heptacyanocyclopentenyliminotriphenylphosphorane. The molecular structure of this adduct (4) and also of (6), 1,2,3,4,5,6-hexacyanohexa-2,4-diene-1,6-diylidenebis(triphenylphosphorane), have been determined by X-ray crystallography.