Catecholase activity of a self-assembling dimeric Cu(II) complex with distant Cu(II) centers

Abstract

Catecholase activity and its mechanistic investigation of a self-assemblying dimeric Cu(II) complex, Cu2L2, where L is N,N′-(ethane-1,2-diyldi-o-phenylene)-bis(pyridine-2-carboxamidide), is presented. The complex was constructed by a spontaneous self-assembly of the organic ligand and Cu(II) ion. X-ray crystallography of Cu2L2(CH3OH)2·2CH3OH, found that the coordination geometry of the Cu(II) site was a distorted square pyramid and two Cu(II) ions were apart by 6.992Å. Though the metal centers are distant, Cu2L2 showed high catecholase activity when 3,5-di-tert-butylcatechol (3,5-H2dtbc) was treated with Cu2L2 in the presence of air at basic condition with kcat of 720h−1 in Michaelis–Menten model. Information collected from the UV–vis kinetic, electron paramagnetic resonance (EPR), and high-resolution electrospray ionization mass spectrometry (ESI MS) measurements on the reaction mixtures could lead the suggestion of the mechanistic pathway of the catecholase activity of Cu2L2 in which each Cu(II) site oxidized 3,5-H2dtbc to 3,5-di-tert-butyl-1,2-benzosemiquinonate anion radical (3,5-dtbq−). Subsequently, 3,5-di-tert-butyl-o-quinone (3,5-dtbq) was formed via both disproportionation and air oxidation of 3,5-dtbq−. Cu2L2 could be reduced to either one- or two-electron reduced state. The reduced complexes were reoxidized by dioxygen molecule accompanying with the generation of hydrogen peroxide.