Comparison of the FeO(2+) and FeS(2+) complexes in the cyanide and isocyanide ligand environment for methane hydroxylation

Abstract

A general comparison of fundamental distinctions between the FeO(2+) and FeS(2+) complexes in an identical cyanide or isocyanide ligand environment for methane hydroxylation has been probed computationally in this work in a series of hypothetical [Fe(IV)(X)(CN)5](3-), [Fe(IV)(X)(NC)5](3-), (X = O, S) complexes. We have detailed an analysis of the geometric and electronic structures using density functional theory calculations. In addition, their σ- and π-mechanisms in C-H bond activation process have been described with the aid of the schematic molecular orbital diagram. From our theoretical results, it is shown that (a) the iron(IV)-sulfido complex apparently is able to hydroxylate C-H bond of methane as good as the iron(IV)-oxo species, (b) the O-CN, S-CN complexes have an inherent preference for the low-spin state, while for the case of O-NC and S-NC in which S = 1 and S = 2 states are relatively close in energy, (c) each of the d block electron orbital plays an important role, which is not just spectator electron, and (d) in comparison to the cyanide and isocyanide ligand environment, we can see that the FeS(2+) species prefer the cyanide ligand environment, while the FeO(2+) species favor the isocyanide ligand environment. In addition, a remarkably good correlation of the σ-/π-mechanism for hydrogen abstraction from methane with the gap between the Fe-dz2 (α) and C-H (α) pair as well as the Fe-dxz/yz (β) and C-H (β) pair has been found.

Keywords: FeO2+; FeS2+; cyanide or isocyanide ligand environment; methane hydroxylation; σ‐ and π‐mechanisms.