Influence of inductive effects and steric encumbrance on the catecholase activities of copper(ii) complexes of reduced Schiff base ligands

Abstract

A series of copper(II) complexes derived from reduced Schiff base ligands has been synthesized and characterized by single-crystal X-ray diffraction and spectroscopic analyses. With the exception of [Cu(Ala5NO₂)(H₂O)] (1a), which crystallized as a mononuclear repeating unit, [Cu₂L₂(H₂O)_x(DMSO)_y]·solvent (L = Ala5H (2), Ala5OMe (3a), Ala5Cl (4a), Ala5Br (5a), Gly5Br (6a), Val5Br (7a) and Leu5Br (8a), x = 1 or 2, y = 0 or 1, solvent = MeOH or DMSO and H₂O) crystallized as phenoxo-bridged dinuclear building units containing Cu₂O₂ cores. In 3a, 4a, 5a, 7a and 8a, the axial positions are occupied by solvent ligands and carboxylate oxygen atoms from adjacent dimers, resulting in the formation of 1D helical coordination polymers. In 6a, a 2D network is constructed by utilizing weak Cu⋯O interactions (∼2.7 Å) with carboxylate groups. All complexes have been investigated for their catecholase activities with 3,5-DTBC, and they show significant catalytic activities except for 1a. The catalytic activities are also observed to increase with increasing +I effects, as well as increase with increasing steric bulkiness on the α-carbon of the carboxylate group.