Theoretical and Experimental Evidence for S_N2 Transition States in Oxidative Addition of Methyl Iodide to cis-[M(CO)_2I_2]- (M = Rh, Ir)

摘要

Oxidative addition of organic molecules to unsaturated transition metal complexes is a fundamental process in oiga-nometallic chemistry and plays a key role in many important catalytic reactions. An important example is the reaction of methyl iodide with cis-[Rh(CO)_2I_2]~-, the rate-determining step in the industrial carbonylation of methanol to acetic acid. In this communication, we present new theoretical and experimental evidence for the nature of the transition state (TS) in this reaction. Ab initio transition structures have been located for nucleophilic attack by cis-[M(CO)_2I_2]~ (M = Rh, Ir) on Mel, and computed secondary a-deuterium kinetic isotope effects (KIEs) for the classical S_N2 mechanism are in excellent agreement with experiment.