Transformation of a Cp*–Iridium(III) Precatalyst for Water Oxidation when Exposed to Oxidative Stress

摘要: The reaction of [Cp*Ir(bzpy)NO3 ] (1; bzpy=2-benzoylpyridine, Cp*=pentamethylcyclopentadienyl anion), a competent water-oxidation catalyst, with several oxidants (H2 O2 , NaIO4 cerium ammonium nitrate (CAN)) was studied to intercept and characterize possible intermediates the oxidative transformation. NMR spectroscopy ESI-MS techniques provided evidence for formation many species that all had intact Ir-bzpy moiety gradually more oxidized Cp* ligand. Initially, an oxygen atom is trapped in between two carbon atoms iridium, which gives oxygen-Ir coordinated epoxide, whereas remaining three are involved η(3) interaction iridium (2 a). Formal addition H2 O 2 a or 1 leads 2 b, double MeCOH functionalization present one engaged iridium. structure 2 b unambiguously determined solid state solution by X-ray single-crystal diffractometry advanced spectroscopic techniques, respectively. Further oxidation led opening transformation diol into diketone carbonyl at metal (2 c). A non-oxygenated carbons "ex-Cp*" also both 2 c. Isolated mixtures 2 a-c were tested catalysis using CAN as sacrificial oxidant. They showed substantially same activity than (turnover frequency values ranged from 9 14 min(-1) ).