Hydroquinone oxidation catalyzed by pyridine-Cu(II) complexes attached to polyorganosiloxanes

Cu(II) complexes of polyorganosiloxanes with pyridyl group in the side chains ( 1–6 ) were investigated as catalysts for hydroquinone oxidation. The catalytic oxidations followed Michaelis-Menten-like kinetics. The kinetic parameters were evaluated, and the greatest value of k₂/K_m is 119 dm³ · mol^?1 · s^?1 due to the large value of k₂ (0,262 s^?1) in methanol/water (vol. ratio 2/1) at 25°C. It has been shown that the main factors which influence the substrate-binding process are hydrophobicity, hydrogen bonding between functional groups in the side chains, conjugation and basicity of pyridine, and adsorption of substrate by amido groups. Large k₂ values were obtained in the present system due to flexibility and hydrophobicity of the siloxane backbone. Additionally, in the activation process, hydrogen bonding between amido groups, which is easily formed due to the flexibility of the polymer chains, should contribute to decrease both activation enthalpy and activation entropy.