Activation of Molecular Oxygen by Biomimetic Schiff Base Complexes of Manganese, Iron, and Cobalt

Abstract

AbstractThe metal complexes (E,E)‐[{diethyl 2,2′‐[1,2‐phenylenebis(iminomethylidyne)]bis[3‐oxobutanoato]}(2–)‐N,N′,O3,O3′]manganese (Mn1a), [3,3′]‐[1,2‐phenylenebis(iminomethylidyne)bis(2,4‐pentanedionato)(2–)‐N,N′,O2,O2′]manganese (Mn1b), and (Z,Z)‐[diethyl 3,3′‐(1,2‐phenylenediimino)bis(2‐cyano‐2‐propenoato)](2–)‐N3,N3′,O1,O1′]manganese (Mn1c) were sythesised and the oxygenation of these complexes was investigated by gas volumetry. All complexes except Mn1c are able to take up oxygen but with different magnitudes. The catalytic activity of the Mn, Co, and Fe complexes of the ligands 1a and 1c and (E,E)‐[{diethyl 2,2′‐[1,2‐ethylenebis(iminomethylidyne)]bis[3‐oxobutanoato]} (2–)N,N′,O3,O3′] iron (Fe1d) and [diethyl (all‐E)‐5,14‐dihydro‐6,17‐dimethyldibenzo[b,i][1,4,8,11]tetraazacyclotetradecine‐7,16‐dicarboxylato)(2–)‐N5,N9,N14,N18]iron (Fe2a) has been compared with respect to the oxidation of hydroquinone by molecular oxygen. The results are interpreted with the aid of electrochemical properties, Lewis acidities, and other relevant factors. However, no simple relationship between the catalytic activity and the other factors could be found.