A new tyrosinase model with 1,3-bis[(2-dimethylaminoethyl)iminomethyl]benzene: Binuclear copper(I) and phenoxo/hydroxo-bridged dicopper(II) complexes

The ligand 1,3-bis[(2-dimethylaminoethyl)iminomethyl]benzene (baib) reacts with [Cu(MeCN)4][ClO4] to form a binuclear copper(I) complex [Cu2I(baib)2][ClO4]2·H2O(1). Crystal structure analysis reveals that the distorted tetrahedral coordination of each copper(I) center is satisfied by one bidentate arm of each ligand. The complex undergoes ready aromatic ring hydroxylation at position 2 of the phenyl ring when reacted with molecular oxygen in MeCN/MeOH/CH2Cl2, producing a four-coordinate μ-phenoxo- and μ-hydroxo-bridged dicopper(II) complex, [Cu2(baib-O)(OH)(OClO3)2] · 1.5H2O (2) (baib-OH: 1,3-bis[(2-dimethylaminoethyl)iminomethyl]phenol). This reaction mimics the reactivity of the copper monooxygenase tyrosinase. A trend is observed for the extent of aromatic ring hydroxylation (25 °C): MeCN > MeOH > CH2Cl2. Cyclic voltammetric experiment of 1 in MeCN reveals an appreciably high redox potential (anodic peak potential, Epa = 0.69 V versus SCE) for the Cu2II/Cu2I redox process. Complex 2 has been characterized by single-crystal X-ray crystallography. Variable temperature (60–300 K) magnetic susceptibility measurements on 2 establish that the copper(II) centers in 2 are antiferromagnetically coupled (2J = −280 cm−1).

Reaction between structurally characterized [Cu2I(baib)2][ClO4]2·H2O and O2 in MeCN/MeOH/CH2Cl2, affords [Cu2II(baib-O)(OH)(OClO3)2]·1.5H2O; magnetism (60–300 K) reveals that the dicopper(II) centers are antiferromagnetically coupled (2J = −280 cm−1).Figure optionsDownload as PowerPoint slide