Carbanionic displacement reactions at phosphorus. Part III. Cyanomethylphosphonate vs. cyanomethylenediphosphonate. Synthesis and solid-state structures

Abstract

The results of the carbanionic reaction between acetonitrile and chlorophosphates depend strongly on the nature of the metallating agent (LiTMP, LDA, LiHMDS). According to the nature of the base, the reaction can be directed towards the formation of either cyanomethylphosphonates 3 or cyanomethylenediphosphonates 5. Electrophilic halogenation of lithiated cyanomethylphosphonate 2a leads to the mono-chloro 17, -bromo 18 and -iodo 19 derivatives. Only the monochloro product 17 is stable enough to be isolated in pure form. The structures of cyanobenzylphosphonate 10b, cyanomethylenediphosphonate 5b and its corresponding lithiated carbanion 4b are determined by X-ray crystallography. The polymeric structure, coupled with a wide charge delocalization, without C–Li contacts, is in agreement with the lack of reactivity towards electrophiles.