C-H activation by multiply bonded complexes with potentially noninnocent ligands: a computational study.

Second- and third-row (typically precious metals) transition metal complexes are known to possess certain electronic features that define their structure and reactivity and are usually not observed in their first-row (base metal) congeners. Can these electronic features be conferred onto first-row transition metals with the aid of noninnocent and/or very high-field ligands? In this research, the impact upon methane C-H bond activation was modeled using the dipyridylazaallyl (smif) supporting ligand for late, first-row transition metal (M) imide, oxo, and carbene complexes (M = Fe, Co, Ni, or Cu; E = O, NMe, or CMe2). Density functional theory calculations suggest that the combination of smif with iron and the oxo activating ligand is the most energetically favorable complex for methane C-H activation. A change in the preferred transition state for methane C-H activation from [2+2] addition to hydrogen atom abstraction was observed upon going from Fe to Cu and for Fe as compared to precious metals. Contrary to expectations, it was the imide ligand rather than the dipyridylazaallyl ligand that was found to possess redox "noninnocent" characteristics.