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 complexes 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 level. 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 associative/ dissociate pathway via the five-coordinated intermediate [Pt(CH₃)(HCCH)(EH₃)(PH₃)₂]. The rate-determining step is the elimination of CH₃EH₃ via 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 barrier for the elimination reaction than the germyl complex. The calculated transition states show that the reason for the lower barrier is the strength of the nascending C-Si bond, which is higher than the C-Ge bond. The results are in agreement with the postulated mechanism of Ozawa et al. (Organometallics, 1998, 17, 1018).