Orthometalated N-(Benzophenoxazine)-o-aminophenol: Phenolato versus Phenoxyl States.
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ABSTRACT: The molecular and electronic structures of the orthometalated ruthenium(III) and osmium(III) complexes of N-(benzophenoxazine)-o-aminophenol (OXLH2) that exhibits versatile redox activities are reported. The redox chemistry of OXLH2 is remarkably different from that of N-(aryl)-o-aminophenol (APLH2). The study established that OXLH2 is redox noninnocent and is a precursor of a phenoxyl radical. One of the C-H bonds of OXLH2 is activated by ions, and OXLH2 reveals three different redox states as dianionic phenolato (OXL2-), monoanionic phenoxyl radical (OXL•-), and zwitterionic phenoxium cation (OXL±) states. The reaction of OXLH2 with [RuII(PPh3)3Cl2] in boiling toluene in air affords an orthometalated OXL2- complex of ruthenium(III), trans-[(OXL2-)RuIII(PPh3)2(Cl)] (1), whereas the similar reaction with [OsII(PPh3)3Br2] yields an orthometalated OXL•- complex, cis-[(OXL•-)OsIII(PPh3)Br2] (2). 1 and 2 exhibit ligand-based reversible redox waves due to OXL•-/OXL2-, OXL±/OXL•-, and MIII/MII couples. The 1 + ion is a OXL•- complex of ruthenium(III). 2 - exhibits temperature-dependent valence tautomerism due to [OsII(OXL•-) ? OsIII(OXL2-)] equilibrium. 2 2- is a OXL2- complex of osmium(II), while 1 2+ and 2 + are OXL± complexes of metal(III). 2 is an oxidant and effective catalyst for oxidation of 3,5-di-tert-butylcatechol to the corresponding quinone, and the turnover number is 119.7 h-1. The UV-vis-NIR absorption spectrum of 1 displays an NIR band at 800 nm due to an intra-ligand-charge-transfer transition, which is absent in 2 incorporating a OXL•- radical. The molecular and electronic structures of 1 and 2 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.
SUBMITTER: Mondal S
PROVIDER: S-EPMC6645054 | biostudies-literature | 2018 Oct
REPOSITORIES: biostudies-literature
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