The reactivity of well defined diiron(III) peroxo complexes toward substrates: Addition to electrophiles and hydrocarbon oxidation

The reactivity of previously reported peroxo adducts [Fe(mu-O-2)(mu-L)(O2CPhCy)(2)(1-Bu-Im)(2)] (1), and [Fe(mu-O-2)(mu-L) (O2CPhCy)(2)(py)(2)] (2), where L is a dinucleating ligand based on the m-xylylenediamine bis(Kemp's triacid imide), toward a variety of substrates is described. These studies were performed to probe the electronic properties of 1 and 2 and evaluate their potential as selective hydrocarbon oxidants. Compound 1 is nucleophilic at -77 degrees C, reacting with phenols and carboxylic acids to liberate hydrogen peroxide, whereas the less electron-rich pyridine analogue 2 is unreactive toward both reagents. By contrast, neither reacts at -77 degrees C with electrophilic reagents such as olefins or triphenylphosphine, or with weak hydrogen atom donors such as dimethylbenzylamine. When solutions of 1 are warmed to room temperature in solvents such as THF, toluene, and cyclopentane, mixtures of alcohol and ketone products derived from the solvent are formed. A detailed investigation of cyclopentane oxidation strongly points to a radical autoxidation pathway. These results are discussed in the context of the selective hydroxylation chemistry that occurs at the carboxylate-bridged diiron centers in soluble methane monooxygenase. (C) 1999 Elsevier Science Ltd. All rights reserved.