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–N_py 2.27 and 2.20 Å). 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.