Reductive functionalization of 3d metal–methyl complexes: The greater importance of ligand than metal

Reductive functionalization of metal–methyl bonds in [M(diimine)2(CH3)(Cl)] complexes (M=VII through CuII) by nucleophilic attack of hydroxide to yield methanol. [Display omitted] •Earlier 3d metals are more convenient for modulating RF barriers.•Highly exergonic pathways with very low energy SN2 barriers were observed.•Reductive functionalization of 3d MII–methyls is not sensitive to d-count. Selective oxidation of methane, which is the primary component of natural gas, to methanol, as a more easily transportable liquid, using organometallic catalysis, has become more important recently due to the abundance of domestic natural gas. In this regard, reductive functionalization (RF) of methyl ligands in [M(diimine)2(CH3)(Cl)] complexes, where M is a 3d metal with oxidation state of 2+ has been studied computationally using density functional techniques. The metal ions chosen for study were VII (d3) through CuII (d9) in the 3d row of the periodic table to assess changes in RF energetics as a function of d orbital occupation. A SN2 mechanism for the nucleophilic attack of hydroxide on the metal–methyl bond, resulting in the formation of methanol, was studied. Similar highly exergonic pathways with very low energy SN2 barriers were observed for the proposed RF mechanism for all the studied complexes. Changes in spin state occurred through the RF pathway for most of the metals studied. To modulate RF pathways closer to thermoneutral for catalytic purposes, a future challenge, paradoxically, requires finding a way to strengthen the metal–carbon bond. Furthermore, the DFT calculations suggest that for 3d metals, ligand properties will be of greater importance than metal identity in identifying suitable catalysts for alkane hydroxylation in which reductive functionalization is used to form the C–O bond.