Evidence for Methane σ-Complexes in Reductive Elimination Reactions from Tp‘Rh(L)(CH₃)H

Abstract

Two sets of experiments are described that provide indirect evidence for the involvement of alkane σ-complexes in oxidative addition/reductive elimination reactions of Tp‘Rh(L)(R)H complexes (Tp‘ = tris-3,5-dimethylpyrazolylborate, L = CNCH2CMe3). First, the methyl deuteride complex Tp‘Rh(L)(CH3)D is observed to rearrange to Tp‘Rh(L)(CH2D)H prior to loss of CH3D. Similarly, Tp‘Rh(L)(CD3)H rearranges to Tp‘Rh(L)(CD2H)D prior to loss of CD3H. Second, the rate of elimination of methane from Tp‘Rh(L)(CH3)H in benzene/perfluorobenzene solvent mixtures is found to be dependent upon the concentration of benzene, indicating an associative component to the reductive elimination of methane. Both of these processes, and their rates, are accommodated by the reversible formation of alkane σ-complexes prior to dissociation of alkane.