Phosphorus–fluorine chemistry. Part XXXV. Unsymmetrical 1,3-diaza-2,4-diphosphetidines of zwitterionic structure

Abstract

The reactions of 2,2,2,4,4,4-hexafluoro-1,3-dimethyl-1,3-diaza-2,4-diphosph(V)etidine with NN′-dilithio-NN′-dimethylethylenediamine, and of the 1,3-t-butyl analogue with t-butyl-lithium gave rise to zwitterionic species, involving tetra- and hexa-co-ordinate phosphorus atoms, instead of the products of normal nucleophilic substitution in which phosphorus retains co-ordination number five. The zwitterionic structure of these products has been established by 1H, 19F, and 31P n.m.r. spectroscopy. Mass spectroscopy has shown that decomposition into monomeric phosphine imides, which is characteristic of 1,3-diaza-2,4-diphosph(V)etidines, does not occur in the case of the zwitterionic compounds.