C–H Activation by Multiply Bonded Complexes with Potentially Noninnocent Ligands: A Computational Study

Abstract

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.

A Two‐Coordinate Cobalt(II) Imido Complex with NHC Ligation: Synthesis, Structure, and Reactivity

“…This reactivity pattern is different to the hydrogen atom abstraction reaction of high‐valent transition‐metal oxo and imido species,22 and is similar to the 1,2‐addition reactions of early‐transition‐metal imido complexes 23. Noting this and also the high variation of the bond strengths of the C(alkynyl)H, C(benzyl)H, and SiH bonds (circa 130, 88, and 91 kcal mol −1 , respectively),24 one could reason that the EH activation reactions by 4 might occur by a concerted [2σ+2π] addition mechanism,25 although a radical‐type hydrogen atom abstraction mechanism22 cannot be absolutely ruled out.…”

Five‐coordinate dinuclar cobalt (II), copper (II), zinc (II) and cadmium (II) complexes with 4‐bromo‐N‐(2‐pyridinylmethylene)benzenamine: Synthesis, characterisation and methyl methacrylate polymerization

“…τ 5 are presented in Table 3 as improved simple metrics for quantitatively evaluating the geometry of the five coordinate complexes. [43,44] The τ 5 Square-pyramidal square-pyramidal 0.00 [43,44] (…”

“…[1][2][3] These complexes showed various coordination modes up to the tetradentate. [4][5][6] Their structural stability and catalytic efficiency made them useful mainly in the area of structural studies, [7] photoluminescence, [8][9][10] spectroscopy, [11] transfer hydrogenation reactions, [12] biological applications, [13] oxidation catalyst, [14] catalysts for alkene polymerization, [15] epoxidation, [16] olefin [17,18] and MMA polymerizations. [19] Poly (methylmethacrylate) (PMMA), an acrylic polymer, is commonly used as a thermoplastic with enhanced optical properties and wide range of industrial applications.…”

New Trends in Oxidative Functionalization of Carbon–Hydrogen Bonds: A Review

“…New types of ligands have been proposed in recent decades which form efficient catalysts with transition metal ions. These ligands are: N-heterocyclic carbene (NHC) [202,203], pincer-like [204][205][206][207][208], redox-active ligands [209][210][211][212], and scorpionates [213][214][215][216][217][218].…”