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)(H 2O)] (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. © 2014 The Royal Society of Chemistry.