A kinetic study on the pairwise competition reaction of α-diazo esters with rhodium(II) catalysts:: Implication for the mechanism of Rh(II)-carbene transfer

The relative rate constants for the Rh(II)-mediated diazo decomposition of a series of para- or meta-substituted diazophenylacetates were measured through intermolecular competition. The kinetic data were further subjected to Hammett correlation analysis and were found to have better linear correlation with sigma (+). Reaction constants for four Rh(II) catalysts have been obtained, Rh-2(OAc)(4) (rho = -1.29 with sigma (+), r = -0.99), Rh-2(Ooct)(4) (rho = -1.31 with sigma (+), r = -0.99), Rh-2(acam)(4) (rho = -1.18 with sigma (+), r = -0.99), Rh-2(O2CCF3)(4) (rho = -1.46 with sigma (+), r = -0.99). The mechanistic implications of these data are discussed.