Exploration of dinuclear systems towards catechol oxidase activity with a novel unsymmetric triazole based bis-bidentate ligand

Abstract

The design and synthesis of a novel asymmetric triazole-based ligand L¹ (N-methyl-3,5-di(pyridin-2-yl)-4H-1,2,4-triazol-4-amine), on which the systematic tuning gave rise to its bisbidentate nature. Corresponding cobalt(II) and nickel(II) complexes ([Co₂(L¹)₂(OH₂)₄]Cl₄; [1](Cl)₄ and [Ni₂(L¹)₂(OH₂)₄]Cl₄; [2](Cl)₄) were synthesized with axial labile aqua molecules for easier susceptibility towards adduct formation. The arrangement of their molecular framework with robust L¹ has been kept planar without the monodentate ligands, which provided reduced steric hindrance for substrate attachment as evident from single crystal X-ray diffraction of [2](Cl)₄. 3,5-ditertbutyl catechol was subjected to oxidation in the presence of catalytic amounts of the complexes, and from the spectrophotometric plots, production of the oxidized product (3,5-ditertbutyl quinone) is confirmed. Further kinetic analysis yielded their turnover numbers (k_cat values) to be 237 h⁻¹ & 327 h⁻¹ respectively. EPR investigations and mass spectroscopy have been performed, and a plausible mechanism has been established from the fragmented molecular peaks of complex-substrate adducts. This study gives insights into choosing suitable ligands for metal ligand cooperativity.