Restricted rotation in methyl- and cyanomethyl-tris-(2,4,6-trimethylphenyl)phosphonium compounds. A 1H nuclear magnetic resonance spectroscopic study. The crystal structure of cyanomethyltris-(2,4,6-trimethylphenyl)phosphonium tetraiodomercurate(II)

Abstract

The crystal structure of cyanomethyltris-(2,4,6-trimethylphenyl)phosphonium tetraiodomercurate(II), [Mes₃-PH₂CN]₂˙Hgl₄^2–, is reported, and the bonding and conformational characteristics of the cation are compared with those related structures which also exist in a propeller conformation. The dynamic stereochemistry of Mes₃PH₂CN, Mes₃PH₃, and Mes₃P, as studies by ¹H n.m.r. spectroscopy, is described. The calculated ΔG^‡values for enantiomerisation of the propeller configuration, assumed to occur via the two-ring flip mechanism, are discussed in the context of related studies. For Mes₃PH₂CN, the enantiomerisation mechanism is related to the conformation in the crystalline state.