Allenic phosphonium borate zwitterions via a phosphonium allenylidene intermediate

Abstract

We describe the synthesis of alkynyl phosphanes of the type R₂P–CC–C(OCH₃)Ph₂ (R = Ph, Cy) and investigate their transformation to geminally substituted phosphonium borato-allene zwitterions upon their reaction with B(C₆F₅)₃. The mechanism for this transformation was studied experimentally and by density functional theory computations (DFT), suggesting the intermediacy of an unsaturated 3-coordinate phosphonium electrophile akin to a methylene phosphonium cation.