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

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)
[(κ3-CNC)­M­(NH2)] complexes via hydrogen
atom abstraction (HAA) and [2 + 2] pathways. Calculations suggest
a significant amide/aminyl, i.e., [(κ3-CNC)2–M3+(NH2)−] ⇔ [(κ3-CNC)2–M2+(NH2)•], 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 ΔG⧧ values being in approximately the upper
20s to mid 30s kcal/mol, 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.