Heterolytic Activaiton of C-H Bond in Methane with (HN = CHCH = NH)M(CH_3) (M = Pd~+, Pt~+, Rh~+, Ir~+, Rh, Ir): Comparative Density Functional Study of Activation Mechanisms

摘要

Activation of methane by oxidative addition and sigma-bond metathesis has been investigated for (N-N)M(CH_3)(M=Pd~+, Pt~+, Rh~+, Ir~+, Rh, Ir; N-N = (HN=CH-CH=NH) using different density functional approaches. The pathway of oxidative addition is in general favored, the exceptions being Pd~+ and Rh~+. Oxidative addition is clearly more favorable for the third-row metal complexes than those of the second row. The third-row metal complexes also tend to have a lower activation barrier for sigma-bond metathesis than those of the second row. In each case, the oxidative addition is preceded by formation of a sigma complex. The bonding energies of these complexes are significantly stronger for the cationic systems.