Carboxylate lability as a factor in the Rh2(carboxylate)4-catalysed cyclopropenation and cyclopropanation of alkynes and alkenes

Abstract

The mechanism of Rh₂(carboxylate)₄-catalysed cyclopropenation and cyclopropanation via two different pathways has been investigated computationally. The two pathways either (a) conserve the Rh₂O₈ framework, with initial coordination of CH₂N₂ and further reaction occurring at an axial acceptor site, or (b) allow dechelation of carboxylate to liberate an equatorial site for activation of bound CH₂N_2. Calculations on the system in question [Rh₂(formate)₄, CH₂N₂, C₂H₄ or C₂H₂] show that both pathways are equally favoured. The importance of coordinated solvent in determining the reaction pathway is demonstrated.