Intra- and Intermolecular C–H Activation by Bis(phenolate)pyridineiridium(III) Complexes

A bis­(phenolate)­pyridine pincer ligand (henceforth abbreviated as ONO) has been employed to support a variety of iridium complexes in oxidation states I, III, and IV. Complexes (ONO)­IrL2Me (L = PPh3, PEt3) react with I2 to cleave the Ir–C bond and liberate MeI, apparently via a mechanism beginning with electron transfer to generate an intermediate Ir­(IV) complex, which can be isolated and characterized for the case L = PEt3. The PPh3 complex is transformed in benzene at 65 °C to the corresponding phenyl complex, with loss of methane, and subsequently to a species resulting from metalation of a PPh3 ligand. Labeling and kinetics studies indicate that PPh3 is the initial site of C–H activation, even though the first observed product is that resulting from intermolecular benzene activation. C–H activation of acetonitrile has also been observed.