Dicopper(II) Complexes of H-BPMP-Type Ligands: pH-Induced Changes of Redox, Spectroscopic (19F NMR Studies of Fluorinated Complexes), Structural Properties, and Catecholase Activities

TLDR: The studies show the pH-dependence for the catalytic abilities of the complexes, related with changes in the coordination sphere of the metal centers, and investigations of the catechol oxidase activities are of interest in modeling thecatecholase enzyme active site and in understanding aspects of structure/reactivity.

Abstract: Substitution of the methyl group from the H-BPMP (HLCH3) ligand (2,6-bis[(bis(2-pyridylmethyl)amino)methyl]-4-methylphenol) by electron withdrawing (F or CF3) or electron donating (OCH3) groups afforded a series of dinucleating ligand (HLOCH3, HLF, HLCF3), allowing one to understand the changes in the properties of the corresponding dicopper complexes. Dinuclear CuII complexes have been synthesized and characterized by spectroscopic (UV−vis, EPR, 1H NMR) as well as electrochemical techniques and, in some cases, by single-crystal X-ray diffraction:  [Cu2(LOCH3)(μΟΗ)][(ClO4)2]·C4H8O, [Cu2(LF)(μΟΗ)][(ClO4)2], [Cu2(LF)(H2O)2][(ClO4)3]·C3D6O, and [Cu2(LCF3)(H2O)2][(ClO4)3]·4H2O. Significant differences are observed for the Cu−Cu distance in the two μ-hydroxo complexes (2.980 A (R = OCH3) and 2.967 A (R = F)) compared to the two bis aqua complexes (4.084 A (R = F) and 4.222 A (R = CF3)). The μ-hydroxo and bis aqua complexes are reversibly interconverted upon acid/base titration. In basic medium, new species are...