Synthesis, structures and catecholase activity of a new series of dicopper(II) complexes of reduced Schiff base ligands

Abstract

A series of dinuclear Cu II complexes of reduced Schiff bases from substituted salicylaldehydes and amino acids have been synthesized and characterized. They are: [Cu 2(RScp11) 2-(H 2O) 2] {H 2RScp11 = 1-[(2-hydroxy-5-R-benzyl) amino]cyclopentane-1-carboxylic acid; R = H (1), Cl (2), CH 3 (3), OH (4)}, [Cu 2(RSch11) 2(H 2O) x] {H 2RSch11 = 1-[(2-hydroxy-5-R-benzyl)amino]cyclohexane-1-carboxylic acid; R = H and x = 1 (5), R = Cl and x = 2 (6), R = CH 3 and x = 2 (7)}, [Cu 2(RSch12) 2-(H 2O) 2] {H 2RSch12 = 2-[(2-hydroxy-5-R-benzyl)amino]cyclohexane-1-carboxylic acid; R = H (8), CH 3 (10) and [Cu 2(ClSch12) 2]·2H 2O (9)}, [Cu 2(Diala5) 2(H 2O) 2]·H 2O [H 3-Diala5 = N-(2,5-dihydroxybenzyl)-L-alanine] (11), [Cu 2-(Diala4) 2(H 2O) 2]·H 2O [H 3Diala4 = N-(2,4-dihydroxybenzyl)-L-alanine] (12), and [Cu 2(Diala3) 2(H 2O) 2] ·H 2O [H 3Diala3 = N-(2,3-dihydroxybenzyl)-L-alanine] (13). They were isolated and characterized by chemical and spectroscopic methods. Single crystal X-ray crystallographic studies have revealed that [Cu 2(Scp11) 2(MeOH) 2] (1a), [Cu 2(ClScp11) 2(DMF)-(H 2O)]·MeCN (2a), [Cu 2(MeScp11) 2(MeOH) 2]·2MeOH (3a), [Cu 2(ClSch11) 2(MeOH) 2]·2 MeOH (6a), [Cu 2(ClSch12) 2]·2MeOH (9a), and [Cu 2(Diala4) 2(DMSO) 2]·2DMSO·2 acetone (12a) have 1D hydrogen-bonded polymeric structures while 4 has a 3D hydrogen-bonded network structure. Complex 8 displays a 2D coordination polymeric network structure. The complexes 1-13 have been investigated as functional models for the catechol oxidase by employing 3,5-di-tert- butylcatechol as a model substrate. Electron-withdrawing substituents reduced the activity while electron-donating substituents enhanced the activity. Variable-temperature magnetic studies conducted on compound 8 suggest the presence of strong inter-dimer antiferromagnetic coupling. © Wiley-VCH Verlag GmbH & Co. KGaA, 2006.