Coordination Complex of Cu(II) with Ligand Containing Carboxylic Acid Group: Synthesis, Characterization and Catecholase Activity

Abstract

Present work reports the synthesis, characterization and catecholase like activity of a diaqua Cu(II) complex of type [(L2–)Cu(H2O)2] (1) with a tridentate ligand (E)-2-(3- hydroxy-3-phenyltriaz-1-en-1- yl)benzoic acid (LH2). Complex 1 is characterized by FT-IR, mass, EPR and UV-Vis spectroscopy. The isotropic hyperfine four line EPR spectrum of complex 1 in solution confirms the Cu(II) state in complex 1. The complex exhibits catalytic activity towards the oxidation of 3,5-di-tert. butyl catechol (3,5-DTBC) to 3,5-di-tert. butyl benzoquinone (3,5-DTBQ) with turnover number (Kcat) = 132.8 h-1 via formation of radical intermediate. The oxidation of 3,5-DTBC in presence of complex 1 is confirmed by the UV-Vis spectroscoy, mass spectra and EPR spectra. Complex 1 is EPR active in solution but the solution containing complex 1 and 3,5-di-tert. butyl catechol is EPR silent authenticating the formation of an organic radical in the catalytic oxidation process. In cyclic voltametry of complex 1, an irreversible cathodic peak appear at -0.19 V may be due to the Cu2+/Cu+ couple and an irreversible anodic wave appear at +1.35 V may be due to the oxidation of N3 – to N3 •–. Cyclic voltammetry of complex 1 with 3,5-DTBC gives a new anodic peak at +0.11 V, which is assigned as cat/sq•– redox couple [cat= 3,5-DTBC, sq•– = benzosemiquinonate anion radical].