On the mechanism of the Rh(II)-catalysed cyclopropanation of alkenes.

The mechanism of Rh(ii)-catalysed cyclopropanation has been investigated computationally using Rh(2)(formate)(4) as a model precatalyst, with the model organic substrates CH(2)N(2) and C(2)H(4) and MeCl as a model for coordinating solvent. Three potential carriers of catalysis have been identified, one retaining the Rh(2)(formate)(4) framework and two others resulting from ligand insertion of Rh-CH(2) 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 CH(2) insertion into the Rh-O bond are more efficient at lowering the activation enthalpy for CH(2)-N(2) scission in the rate determining step.