Synthesis, Structures and Catecholase Activity of a New Series of Dicopper(II) Complexes of Reduced Schiff Base Ligands

Abstract

AbstractA series of dinuclear CuII complexes of reduced Schiff bases from substituted salicylaldehydes and amino acids have been synthesized and characterized. They are: [Cu2(RScp11)2(H2O)2] {H2RScp11 = 1‐[(2‐hydroxy‐5‐R‐benzyl)amino]cyclopentane‐1‐carboxylic acid; R = H (1), Cl (2), CH3 (3), OH (4)}, [Cu2(RSch11)2(H2O)x] {H2RSch11 = 1‐[(2‐hydroxy‐5‐R‐benzyl)amino]cyclohexane‐1‐carboxylic acid; R = H and x = 1 (5), R = Cl and x = 2 (6), R = CH3 and x = 2 (7)}, [Cu2(RSch12)2(H2O)2] {H2RSch12 = 2‐[(2‐hydroxy‐5‐R‐benzyl)amino]cyclohexane‐1‐carboxylic acid; R = H (8), CH3 (10) and [Cu2(ClSch12)2]·2H2O (9)}, [Cu2(Diala5)2(H2O)2]·H2O [H3Diala5 = N‐(2,5‐dihydroxybenzyl)‐L‐alanine] (11), [Cu2(Diala4)2(H2O)2]·H2O [H3Diala4 = N‐(2,4‐dihydroxybenzyl)‐L‐alanine] (12), and [Cu2(Diala3)2(H2O)2]·H2O [H3Diala3 = 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 [Cu2(Scp11)2(MeOH)2] (1a), [Cu2(ClScp11)2(DMF)(H2O)]·MeCN (2a), [Cu2(MeScp11)2(MeOH)2]·2 MeOH (3a), [Cu2(ClSch11)2(MeOH)2]·2 MeOH (6a), [Cu2(ClSch12)2]·2 MeOH (9a), and [Cu2(Diala4)2(DMSO)2]·2 DMSO·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, 69451 Weinheim, Germany, 2006)