Evidence for methane sigma-complexes in reductive elimination reactions from Tp ' Rh(L)(CH3)H

Two sets of experiments are described that provide indirect evidence for th e involvement of alkane sigma-complexes in oxidative addition/reductive eli mination reactions of Tp'Rh(L)(R)H complexes (Tp' = tris-3,5-dimethylpyrazp lylborate, 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; Simil arly, Tp'Rh(L)(CD3)H rearranges to Tp'Rh(L)(CD2H)D prior to loss of CD3H. S econd, the rate of elimination of methane from Tp'Rh(L)(CH3)H in benzene/pe rfluorobenzene solvent mixtures is found to be dependent upon the concentra tion of benzene, indicating an associative component to the reductive elimi nation of methane. Both of these processes, and their rates, are accommodat ed by the reversible formation of alkane sigma-complexes prior to dissociat ion of alkane.