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

A mononuclear Cu(II) complex [Cu-II(L)](1) [H2L-N,M-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 P2(1)2(1)2(1) with a = 9.9794 angstrom, b 11.944 angstrom, c =28.719 angstrom. Single crystal X-ray diffraction study reveals that in mono nuclear copper(II) complex [Cu-II(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 (E-1/2 = 0.56 V and E-1/2 = 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-tertbutylcatechol in methanol solvent to its corresponding quinone derivative in aerial oxygen. The kinetic parameters have been determined using Michaelis-Menten approach. The K-cat value for 1 in methanol is 722 h(-1). (C) 2019 Elsevier B.V. All rights reserved.