On the mechanism of the Rh(ii)-catalysed cyclopropanation of alkenes

Abstract

The mechanism of Rh(II)-catalysed cyclopropanation has been investigated computationally using Rh₂(formate)₄ as a model precatalyst, with the model organic substrates CH₂N₂ and C₂H₄ and MeCl as a model for coordinating solvent. Three potential carriers of catalysis have been identified, one retaining the Rh₂(formate)₄ framework and two others resulting from ligand insertion of Rh–CH₂ into an Rh–O bond. Both 2 + 1 and 2 + 2 pathways have been identified for the cyclopropanation step depending on the catalytic carrier involved. Complexes resulting from CH₂ insertion into the Rh–O bond are more efficient at lowering the activation enthalpy for CH₂–N₂ scission in the rate determining step.