Synthesis, structure, DFT study and catechol oxidase activity of Cu(II) complex with sterically constrained phenol based ligand

Abstract

A mononuclear Cu(II) complex [CuII(L)](1) [H2L=N,N′-bis(2-hydroxy-3,5-di tertiarybutylbenzyl)-homopiperazine] has been synthesized by using sterically constrained tetradentate phenol-based ligand. Characterization of this compound has been carried out by various spectroscopic tools. Compound 1 crystallizes in orthorhombic space group P212121 with a = 9.9794 Å, b = 11.944 Å, c = 28.719 Å. Single crystal X-ray diffraction study reveals that in mono nuclear copper(II) complex [CuII(L) ] 1, the metal center adopts a square planar environment. The geometry of the Cu(II) complex has been optimized using density functional theory (DFT) calculations. Electronic excitation energies of the above mentioned complex are calculated by TDDFT/UB3LYP method combined with the SMD solvation in methanol medium. Electrochemical nature of the bis phenol based copper complex confirms that both the oxidation process (E1/2 = 0.56 V and E1/2 = 0.89 V) arise due to ligand based oxidation of the phenol moiety to phenoxyl radical. Compound 1 acts as an effective catalyst towards the oxidation of 3,5-di-tert-butylcatechol in methanol solvent to its corresponding quinone derivative in aerial oxygen. The kinetic parameters have been determined using Michaelis–Menten approach. The Kcat value for 1 in methanol is 722 h−1.