H2O2-reactivity of copper(II) complexes supported by tris[(pyridin-2-yl)methyl]amine ligands with 6-phenyl substituents

Article abstract of DOI:10.1021/ic801568g

The structure and H₂O₂-reactivity of a series of copper(II) complexes supported by tris[(pyridin-2-yl)methyl]amine (TPA) derivatives having a phenyl group at the 6-position of pyridine donor group(s) [(6-phenylpyridin-2-yl)-methyl]bis[(pyridin-2-yl)methyl]amine (Ph ₁TPA), bis[(6-phenylpyridin-2-yl)methyl][(pyridin-2-yl)methyl]amine (Ph₂TPA), and tris[(6-phenylpyridin-2-yl)methyl]amine (Ph ₃TPA) have systematically been examined to get insights into the aromatic substituent (6-Ph) effects on the coordination chemistry of TPA ligand system. The X-ray crystallographic analyses have revealed that [Cu ^II(TPA)(CH₃CN)](ClO₄)₂ (CuTPA) and [Cu^II(Ph₃TPA)(CH₃CN)](ClO₄) ₂ (3) exhibit a trigonal bipyramidal structure, whereas [Cu ^II(Ph₁TPA)(CH₃CN)](ClO₄) ₂ (1) shows a slightly distorted square pyramidal structure and [Cu^II(Ph₂TPA)(CH₃CN)](ClO₄) ₂ (2) has an intermediate structure between trigonal bipyramidal and square pyramidal. On the other hand, the UV-vis and ESR data have suggested that all the copper(II) complexes have a similar trigonal bipyramidal structure in solution. The redox potentials of CuTPA, 1, 2, and 3 have been determined as E_1/2 = -0.34, -0.28, -0.16, and -0.04 mV vs Ag/AgNO₃, respectively, demonstrating that introduction of each 6-Ph group causes positive shift of E_1/2 about 0.1 V. Notable difference in H₂O ₂-reactivity has been found among the copper(II) complexes. Namely, CuTPA and 1 afforded mononuclear copper(II)-hydroperoxo complexes CuTPA-OOH and 1-OOH, respectively, whereas complex 2 provided bis(μ-oxo)dicopper(III) complex 2-oxo. On the other hand, copper(II) complex 3 was reduced to the corresponding copper(I) complex 3^red. On the basis of the H ₂O₂-reactivity together with the X-ray structures and the redox potentials of the copper(II) complexes, the substituent effects of 6-Ph are discussed in detail.