Interaction of 2-(2′,6′-dialkylphenylazo)-4-methylphenols with iridium. C–H activation and migration of alkyl group

Reaction of 2-(2′,6′-diethylphenylazo)-4-methylphenol (L2) with [Ir(PPh3)3Cl] afforded two organoiridium complexes 3 and 4 via C–H bond activation of an ethyl group in the arylazo fragment of the L2 ligand. In both the complexes the azo ligand binds to iridium as a dianionic tridentate C,N,O-donor. Two triphenylphosphines and a hydride (in the case of complex 3) or chloride (in the case of complex 4) are also coordinated to the metal center. A similar reaction of [Ir(PPh3)3Cl] with 2-(2′,6′-diisopropylphenylazo)-4-methylphenol (L3) yielded another organoiridium complex 5, where migration of one iso-propyl group from its original location (say, the 2′ position) to the corresponding third position (say, the 4′ position) took place through C–C bond activation. In this complex the modified azo ligand binds to iridium as a dianionic tridentate C,N,O-donor. Two triphenylphosphines and a hydride are also coordinated to the metal center. The structures of complexes 3 and 4 have been optimized through DFT calculations. The structure of complex 5 has been determined by X-ray crystallography. All the complexes show characteristic 1H NMR signals and intense transitions in the visible region. Cyclic voltammetry on all the complexes shows an oxidation within 0.66–1.10 V vs SCE, followed by a second oxidation within 1.15–1.33 V vs SCE and a reduction within −0.96 to −1.07 V vs SCE.