Extensive research effort has been directed toward the development of transition metal catalysts for the selective oxidation of hydrocarbons. Inspired by nonheme iron oxygenases that activate molecular oxygen to carry out a variety of hydrocarbon oxidation reactions with high selectivity, we and others have reported hydrocarbon oxidations catalyzed by nonheme iron complexes using HOOH as oxidant. Mechanistic studies reveal the formation of an S = 1/2 Fe(III)-OOH intermediate that undergoes water-assisted, rate-determining O-O bond cleavage to afford an FeV(O)(OH) oxidant that carries out the oxidative transformations. Addition of acetic acid (AcOH) leads to the formation of a different intermediate that has been proposed to be an FeV(O)(OAc) species based on its novel g = 2.7 EPR signal. We have recently characterized this species as an S = 1/2 Fe(III)-OOAc complex by a combination of EPR, Mossbauer and resonance Raman spectroscopies. Kinetics studies show that the decay rate of this species is not affected by substrate concentration, while DFT calculations show that the Fe(III)-OOAc intermediate undergoes reversible O-O cleavage to afford an S = 1/2 FeIV(O)(OAc�) species that ultimately undergoes spin change to become an FeV(O)(OAc) species that oxidizes substrates without a barrier. Our mechanistic studies on the evolution of the Fe(III)-OOAc species and its involvement in the catalytic hydrocarbon oxidation reactions will be presented.

Role of a nonheme Fe(III)-OOAc intermediate in bio-inspired iron-catalyzed hydrocarbon oxidations

248th National Meeting (2014)

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