Catechol oxidation: activity studies using electron-rich nitrogen-based ligands

We have studied the oxidation of catechol to o -quinone with atmospheric dioxygen at ambient conditions by in situ generated copper (II) complexes of five electron-rich nitrogen ligands: (3,5-dimethyl-pyrazol-1-yl)-methanol L1 ; 3-benzylamino-propionitrile L2 ; 3-[benzyl-(3,5-dimethyl-pyrazol-1-ylmethyl)-amino]-propionitrile L3 ; {3-[(2-cyano-ethyl)-(1,5-dimethyl-1H-pyrazol-3-ylmethyl)-amino]-propyl}-(1,5-dimethyl-1H-pyrazol-3-ylmethyl)-amino]-propionitrile L4 and 3-[{2-[(2-cyano-ethyl)-(1,5-dimethyl-1H-pyrazol-3-ylmethyl)-amino]-ethyl}-(1,5-dimethyl-1H-pyrazol-3-ylmethyl)-amino]-propionitrile L5 . We found that all complexes catalyze the oxidation reaction with different rates depending on three parameters: the nature of the ligand, the nature of ion salts, and the concentration of the complex. The combination of L3 (CuSO 4 ) gave the highest rate of this activity about 8.71 μmol 1 /L 1 /min 1 .