The synthesis and characterisation of R3PXCN [R = 2,4,6-(CH3O)3-C6H2, 2,6-(CH3O)2C6H3, NCCH2CH2, C6H11 or PhCH2; X = Br or I] in the solid state and in solution

The compounds R3PXCN [R = 2,4,6-(CH3O)(3)C6H2, 2,6-(CH3O)(2)C6H3, NCCH2CH2, C6H11 or PhCH2; X = Br or I] have been synthesized and characterised by elemental analysis, X-ray powder diffraction and infrared and P-31-{H} NMR spectroscopy. In the solid state and in solution the compounds exist as mixtures of the ionic compounds [R3PCN]X and [R3PX]CN with no evidence for the species R3PX2 or R3P(CN)(2). Infrared studies indicate the presence of both covalently bound and ionic cyanide. The P-31-{H} NMR studies show that in CDCl3 the compounds exist predominantly as [R3PCN]X, although a minor component due to [R3PX]CN is also observed in ca. 10:1 ratios. These novel compounds are discussed with reference to the analogous R3PX2 compounds. An X-ray crystallographic study of [{2,4,6-(CH3O)(3)C6H2}(3)PCN]I reveals an ionic structure with no long cation-anion interactions. In contrast, the crystal structure of [2,4,6-(CH3O)(3)C6H2](3)PI2 represents a further example of the molecular four-co-ordinate charge-transfer structure R3P-I-I; d(I-I) for this compound, 3.3394(5) Angstrom, is rather short considering the very high basicity of the parent tertiary phosphine [cf. d(I-I) for PhMe2PI2 = 3.408(5) Angstrom].