Theoretical investigation on the mechanism of oxygen atom transfer between two non-heme iron centres

Density functional theory calculations are presented on the oxygen atom transfer reaction between two non-heme iron centres: One contains Bn-tpen [N-benzyl-N,N′,N′-tris(2-pyridylmethyl) ethane-1,2-diamine], whereas the other contains N4Py [N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine]. The calculations show that the (Bn-tpen)Fe-O-Fe(N4Py) complex is a stable entity but considerably higher in energy than isolated species. However, a mechanism of oxygen atom transfer from one non-heme iron centre to the other will proceed via this oxido-bridged intermediate. This oxido-bridged complex has both iron atoms in oxidation state III so that in the process of the formation of the complex, an electron transfer from the Fe^II centre to the Fe^IV(O) centre has taken place. Nevertheless, both metal atoms have different orbital and spin-density occupation. A large solvent effect on the reaction barriers is obtained, indicating that the reaction proceeds only in very polar environments.