An Unexpected Mu(4)-Oxido-Bridged Tetranuclear Cu(Ii) Inverse Coordination Complex Of A Heptadentate Bis(Pyrazolyl)Methane-Based Ligand: Synthesis, Structure, Spectroscopic Properties, And Catecholase Activity

A new tetranuclear copper(II) complex, {Bu-t-C6H2(O)[CH = N-CH2-CH(pz)(2)](2)}(2)Cu-4(mu(4)-O)(OAc)(4) (L2Cu4(mu(4)-O) (OAc)(4), pz = pyrazolyl ring) has been prepared from the condensation reaction of 4-tert-butyl-2,6-diformylphenol with two equivalents of bis(pyrazolyl)ethanamine moieties in the presence of two equivalents of copper (II) acetate. The complex has been characterized by X-ray diffraction studies in solid state, as well as by UV-Vis, IR, and ESI spectroscopies. The structure of this inverse coordination complex consists of a central oxygen ion surrounded by four copper(II) cations residing in the corners of a distorted tetrahedron; the remaining coordination sites of the Cu2+ ions are filled by imine donors and acetate counter-ions, leaving the bis(pyrazolyl) methane donor groups uncoordinated to the copper(II) centers. In contrast to the solid-state structure, this compound was found to be dinuclear in solution, LCu2(OAc)(2)(OH). The complex catalyzes the oxidation of 3,5-di-tert-butylcatechol (DTBC) and 4-tert-butylcatechol (TBC) to their corresponding quinones. The catalytic mechanism was investigated using DTBC as a substrate, and it was found that the oxidation reaction occurs via two different pathways, one involving molecular oxygen and the other hydrogen peroxide as oxidants.