Ligand Tuning in Pyridine-Alkoxide Ligated CpIr III Oxidation Catalysts

Six novel derivatives of pyridine-alkoxide ligated Cp*IrIII complexes, potent precursors for homogeneous water and C–H oxidation catalysts, have been synthesized, characterized, and analyzed spectroscopically and kinetically for ligand effects. Variation of alkoxide and pyridine substituents was found to affect their solution speciation, activation behavior, and oxidation kinetics. Application of these precursors to catalytic C–H oxidation of ethyl benzenesulfonate with aqueous sodium periodate showed that the ligand substitution pattern, solution pH, and solvent all have pronounced influences on initial rates and final conversion values. Correlation with O2 evolution profiles during C–H oxidation catalysis showed these competing reactions to occur sequentially, and demonstrates how it is possible to tune the activity and selectivity of the active species through the N^O ligand structure.