DFT study of the reactivity of methane and dioxygen with d 10-L 2M complexes

Abstract

A density functional theory analysis of the reactions of methane and O 2 with d 10-L 2M complexes (M = Pd, Pt; L = N-heterocyclic carbene (NHC), PMe 3) is presented. Computations suggest that reaction of L 2M 0 with O 2/CH 4 to form cis- (L) 2M(OOH)(CH 3) is only slightly uphill (ΔG ∼ 10–11 kcal/mol). Based on calculated thermodynamics, reaction of (L) 2Pt 0 with CH 4 and O 2 is predicted to be more favorable by first addition of CH 4 and then reaction of O 2 with the resulting methyl–hydrido complex. However, oxidative addition for either the C–H bond of methane or of O 2 to d 10-L 2M complexes is kinetically prohibitive. If barriers to oxidative addition to d 10-L 2M systems could be reduced, conversion of L 2M(H)(CH 3) to L 2M(OOH)(CH 3) via hydrogen atom abstract/radical rebound is calculated to be thermodynamically and kinetically feasible, particularly for NHC and Pd. As (NHC) 2Pd also has a lower free energy to methane C–H oxidative addition than does (NHC) 2Pt, the former combination would appear to be a promising starting point in the search for catalysts for partial hydrocarbon oxidation.