Synthesis and Characterization of Bio-Inspired Diiron Complexes and Their Catalytic Activity for Direct Hydroxylation of Aromatic Compounds

Three [FeFe]-hydrogenase model complexes [(-dmedt){Fe(CO)(3)}(2)] [1; dmedt = SCH(CH3)CH(CH3)S], [(-dmedt){Fe(CO)(3)}{Fe (CO)(2)PPh3}] (1-PPh3), and [(-dmest){Fe(CO)(3)}(2)] [1-O; dmest = SCH(CH3)CH(CH3)S(O)], 1-O were synthesized and characterized. These model complexes, which are generally used as the functional biomimics of the hydrogen-producing dinuclear active site in [FeFe]-hydrogenase, were used as efficient catalysts for the selective hydroxylation of aromatic compounds to phenols under mild conditions. Because both the dithiolato-sulfur site and the Fe-Fe bond in the model complexes were possible active oxidation sites, DFT calculations were used to investigate the oxygenated products, that is, the S-oxygenated products or the Fe-oxygenated forms of the model complexes, which may be involved in the catalytic cycle. The experimental and computational results indicate that the thermodynamically favored Fe-oxygenated intermediates dominate the hydroxylation of the aromatic compounds. A possible mechanism for the hydroxylation is also proposed.