Orthometalated -(Benzophenoxazine)--aminophenol: Phenolato versus Phenoxyl States.

The molecular and electronic structures of the orthometalated ruthenium(III) and osmium(III) complexes of -(benzophenoxazine)--aminophenol (LH) that exhibits versatile redox activities are reported. The redox chemistry of LH is remarkably different from that of -(aryl)--aminophenol (LH). The study established that LH is redox noninnocent and is a precursor of a phenoxyl radical. One of the C-H bonds of LH is activated by ions, and LH reveals three different redox states as dianionic phenolato (L), monoanionic phenoxyl radical (L), and zwitterionic phenoxium cation (L) states. The reaction of LH with [Ru(PPh)Cl] in boiling toluene in air affords an orthometalated L complex of ruthenium(III), -[(L)Ru(PPh)(Cl)] (), whereas the similar reaction with [Os(PPh)Br] yields an orthometalated L complex, -[(L)Os(PPh)Br] (). and exhibit ligand-based reversible redox waves due to L/L, L/L, and M/M couples. The ion is a L complex of ruthenium(III). exhibits temperature-dependent valence tautomerism due to [Os(L) ↔ Os(L)] equilibrium. is a L complex of osmium(II), while and are L complexes of metal(III). is an oxidant and effective catalyst for oxidation of 3,5-di--butylcatechol to the corresponding quinone, and the turnover number is 119.7 h. The UV-vis-NIR absorption spectrum of displays an NIR band at 800 nm due to an intra-ligand-charge-transfer transition, which is absent in incorporating a L radical. The molecular and electronic structures of and and their oxidized and reduced analogues were confirmed by single-crystal X-ray crystallography, variable-temperature electron paramagnetic resonance spectroscopy, spectroelectrochemical measurements, and density functional theory calculations.