Computational Study of Methane C-H Activation by Earth-Abundant Metal Amide/Aminyl Complexes

摘要

Density functional theory, augmented by multiconfiguration SCF (MCSCF) simulations, was used to understand the factors that control methane C-H activation by Earth-abundant, 3d metal (Cr-Ni) [(kappa(3)-CNC)M(NH2)] complexes, via hydrogen atom abstraction (HAA) and [2 + 2] pathways. Calculations suggest a significant amide/aminyl, i.e., [(kappa(3)-CNC)M-2-(3+)-(NH2)(-)] double left right arrow [(kappa(3)-CNC)M-2-(2+)(NH2)(center dot)], admixture in the electronic ground 'States, of these complexes and thus significant unpaired electron density (radical character) on:the NH2 ligand. The spin coupling between the aminyl radical and spin density on the central metal ion is interesting, particularly for the:cobalt aminyl complex, in which both ferromagnetic and antiferromagnetic triplet states are found to be close in energy via both DFT and MCSCF methods. Modeled complexes are computed to have reasonable barriers to methane activation,. with, Delta G(double dagger) values being in approximately the upper 20s to mid 30s kcal/cool, generally decreasing toward the right in the 3d series, which loosely tracks with spin density (radical character) on the aminyl nitrogen, a switch from [2 + 2] to HAA activation pathways, and more favorable thermodynamics for C-H scission.