Synthesis, structure, and catecholase activity of bispyrazolylacetate copper(ii) complexes

Abstract

A series of six-coordination copper(II) complexes containing bis(3,5-di-t-butylpyrazol-1-yl)acetate (bdtbpza) and N-heterocycles or chelating aliphatic ligands have been synthesized. The steric bulkiness of bis(pyrazol-1-yl)acetate anchors two bdtbpza to situate a trans position and to adopt an O-bound monodentate coordination mode with other nitrogen bases occupying the basal plane. Five mononuclear mixed ligand complexes, [Cu(bdtbpza)₂(py)₄] 1, [Cu(bdtbpza)₂(t-Bupy)₄] 2, [Cu(bdtbpza)₂(pym)₂(MeOH)₂] 3, [Cu(bdtbpza)₂(eda)₂] 4, [Cu(bdtbpza)₂(tmeda)(H₂O)₂] 5, where py = pyridine, t-Bupy = tert-butylpyridine, pym = pyrimidine, eda = ethylenediamine, and tmeda = tetramethylethylenediamine, were isolated and thoroughly characterized. Intriguingly, the heteroleptic complex 5, which has two aquo-ligands oriented in the cis positions, demonstrates higher catecholase-like activity in performing aerial oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC) to 3,5-di-tert-butylquinone (3,5-DTBQ) than other bis(pyrazolyl)acetate-embedded copper complexes reported herein, which suggests the essential role of labile cis-aquo ligands to promote the catalytic reaction.