Promotion of phosphaalkyne cyclooligomerisation by a Sb(v) to Sb(iii)redox process

Abstract

A high yield of the tetraphosphaladderene, anti-tetraphosphatricyclo[4.2.0.0^2,5]octa-3,7-diene, is obtained from reaction of the zirconocene 1,3-diphosphabicyclo[1.1.0]butane with Ph₂SbCl₃ in THF or CH₂Cl₂. Exploration of the reaction pathway using density functional theory suggests that an envelope-type adduct of Ph₂SbCl and 1,3-diphosphabicyclo[1.1.0]butane plays a pivotal role in the reaction. The zwitterionic character of this intermediate species allows it to act simultaneously as both an ene and an eneophile, and a symmetry-allowed bimolecular reaction leads to the tetraphosphaladderene species via a spirocyclic intermediate.