Models for Copper‐Dioxygen Complexes: The chemistry of copper(II) with some planar tridentate nitrogen ligands

Abstract

AbstractThe solution chemistry of Cu(II) with a series of five planar tridentate nitrogen ligands, 2,6‐bis(benzimidazol‐2‐yl)pyridine (bzimpy, 1), 2,6‐bis(l‐methylbenzimidazol‐2‐yl)pyridine (mbzimpy, 2) 2,6‐bis(benzothiazol‐2‐yl) pyridine (bzthpy, 3), 2,6‐bis(benzoxazol‐2‐yl)pyridine (bzoxpy, 4), and 2,2′, 6′, 2″‐terpyridyl (terpy, 5) is reported. Electronic and EPR spectra are consistent with the complexes [CuL]2+ having essentially tetragonal structure in solution, with the fourth coordination site in the plane of the ligand occupied by solvent. bzthpy and bzoxpy show smaller ligand‐field splittings than bzimpy, mbzimpy, and terpy, and are easily decomplexed from the copper. Substitution of the coordinated solvent molecule in the plane of the ligand is observed with Cl− and OH− (provided that the ligand has no acidic protons) for all ligands except terpy. The reaction between [Cu(mbzimpy)]2+ and imidazole has been studied by potentiometric titration in MeCN/H2O 1:1 and shows strong binding of the imidazole in the plane (log K = 4.5 at 25°), and also the formation of an imidazolate‐bridged dinuclear species.