Heteroleptic tripodal complexes of copper(II): towards a synthetic model for the active site in galactose oxidase

Abstract

A series of copper(II) complexes derived from tripodal ligands (HL) bearing pyridyl and phenolic arms have been synthesized and characterized. The molecular structures of complexes [CuL4(O2CMe)]·H2O and [CuL4(SCN)]·MeCO2Et {HL4= 2-bis[2-(2-pyridyl)ethyl]aminomethyl-4-nitrophenol} were determined by X-ray diffraction; the complexes exist as neutral, mononuclear species in the solid state. The co-ordination geometry around the copper atom in each is a distorted square-based pyramid (τ= 0.08 and 0.11) where one pyridyl nitrogen occupies the axial position (Cu–Npy 2.27 and 2.20 A). Three ligand donor atoms comprising the square plane are unchanged but the fourth ligand is an exogenous donor atom from MeCO2– or SCN– respectively. Reference is made to the relationship of the structures to that found at the copper(II) centre at the active site of galactose oxidase.