A Structural Study of a Novel MMO Model, [Fe2O(H2O)2(tris((1-methylimidazol-2-yl)methyl)amine)2]4+, and New Mechanistic Aspects of Alkane Functionalization Including Enhanced Catalytic Activity of the Aqua Complex

A new biomimetic structural model of the active site of the MMO enzyme, [Fe2O(H2O)2(tris((1-methylimidazol-2-yl)methyl)amine)2]4+, has been characterized by single-crystal X-ray analysis and shown to functionalize cyclohexane, toluene, adamantane, propane, and ethane, in the presence of t-butyl hydroperoxide (TBHP) and O2 gas, with rates that are faster than the comparable mu-OAc bridged complex. This supports a mechanism of ligand replacement by the oxidant, TBHP, as rate -determining step in the formation of the active FeOFe=O oxidant. The use of a radical clock substrate, trans-2-phenylmethylcyclopropane, to support a free radical mechanism for the functionalization process, shows only ring-opened products, 1-phenyl-but-3-en-1-ol and a trace of its corresponding ketone. Thus, the initially formed cyclopropylcarbinyl radical rapidly rearranges to the 1-phenyl-but-3-enyl radical before O2 trapping to form a hydroperoxide.