Phosphorus lone pairs stabilization of carbocations: the synthesis and dynamics of unsymmetrical methylene phosphonium ions

Abstract

Halide abstractions from P-chlorinated phosphorus ylides 9a–c either by AlCl₃ or SnCl₂ yield unsymmetrical methylene phosphonium ions 10a–c in which energy barriers > 83 kJ mol^–1 for the rotation around the PC have been estimated by NMR techniques. The salts with AlCl₄^– counteranions are stable, but compounds with SnCl₃^– anions decompose stereoselectively to unsymmetrical methylene phosphanes, SnCl₂, and Bu^tCl.