Iron-catalyzed oxidation of unreactive C-H bonds: Utilizing bio-inspired axial ligand modification to increase catalyst stability

Three different bio-inspired Fe(II) complexes are applied as powerful catalysts for the oxidation of unreactive C-H bonds under ambient conditions. Cyclohexane as the main model substrate is oxidized to cyclohexanol, cyclohexyl hydroperoxide, and cyclohexanone. Alcohol + cyclohexyl hydroperoxide to ketone ratios ((A + H)/K) of up to 26 are obtained with comparatively high turnovers of up to 43. Bio-inspired modification of the Fe(II) complexes in the axial positions is used to increase catalyst stability toward hydrogen peroxide, leading to an increase in turnovers of up to 34%. Several parameters for the catalytic oxidation are investigated, e.g., the amount and type of oxidant, reaction temperature, and the relative catalyst concentration. Among others, 9,10-dihydroantracene and 2,3-dimethylbutane are used as substrates for the catalytic C-H bond oxidation.