A theoretical study of the reductive elimination of CH3EH3 from cis-[Pt(CH3)(EH3)(PH3)(2)] (E = Si, Ge) in the presence of acetylene

The reaction mechanism of the elimination of CH3EH3 from the platinum compl exes cis-[Pt(CH3) (EH3)(PH3)(2)] (E = Si, Ge) in the presence of acetylene has been studied using gradient-corrected DFT calculations at the B3LYP lev el. The reaction proceeds in two steps. The first step is the formation of the acetylene complex [Pt(CH3) (HCCH) (EH3)(PH3)] which occurs in a associa tive/dissociate pathway via the five-coordinated intermediate [Pt(CH3) (HCC H) (EH3)(PH3)(2)] The rate-determining step is the elimination of CH3EH3 vi a a four-coordinated transition state. The alternative mechanism via direct dissociation from the five-coordinated intermediates has higher activation barriers. The calculated activation energies of the model reactions are in good agreement with experimental results. The silyl complex has a lower ba rrier for the elimination reaction than the germyl complex. The calculated transition states show that the reason for the lower barrier is the strengt h of the nascending C-Si bond, which is higher than the C-Ge bond. The resu lts are in agreement with the postulated mechanism of Ozawa et al.