Computational Study of Methane C-H Activation by First-Row Late Transition Metal LnM=E (M: Fe, Co, Ni) Complexes

摘要

Methane functionalization via LnM=E active species (L-n = beta-diketiminate, dihydrophosphinoethane; M = Fe-Ni, E = NCF3, NCH3, O) through a hydrogen atom abstraction (HAA)/radical rebound (RR) mechanism is calculated to be thermodynamically and kinetically feasible. The enthalpies of each reaction decrease in the order Fe > Co > Ni and with the proximity of CF3 supporting ligand substituents ("fluorination") to the metal center. For HAA, lower abstraction enthalpies were calculated for L-n = beta-diketiminate and E = NCF3 rather than dhpe and NCH3, respectively, whereas the opposite trend was found for RR enthalpies. The overall functionalization thermodynamics were optimal for L-n = beta-diketiminate and E = NCH3, with similar enthalpies for E = O when M = Ni. The HAA kinetics further implicate fluorinated (beta-diket)Ni=O as the most promising methane functionalization complexes, with calculated activation barriers as low as 8.1 kcal mol(-1).