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

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 2 O) 2 ] {H 2 RScp11 = 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 2 O) x ] {H 2 RSch11 = 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 2 O) 2 ] {H 2 RSch12 = 2‐[(2‐hydroxy‐5‐R‐benzyl)amino]cyclohexane‐1‐carboxylic acid; R = H ( 8 ), CH 3 ( 10 ) and [Cu 2 (ClSch12) 2 ] · 2H 2 O ( 9 )}, [Cu 2 (Diala5) 2 (H 2 O) 2 ] · H 2 O [H 3 Diala5 = N ‐(2,5‐dihydroxybenzyl)‐ L ‐alanine] ( 11 ), [Cu 2 (Diala4) 2 (H 2 O) 2 ] · H 2 O [H 3 Diala4 = N ‐(2,4‐dihydroxybenzyl)‐ L ‐alanine] ( 12 ), and [Cu 2 (Diala3) 2 (H 2 O) 2 ] · H 2 O [H 3 Diala3 = 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 2 O)] · MeCN ( 2a ), [Cu 2 (MeScp11) 2 (MeOH) 2 ] · 2 MeOH ( 3a ), [Cu 2 (ClSch11) 2 (MeOH) 2 ] · 2 MeOH ( 6a ), [Cu 2 (ClSch12) 2 ] · 2 MeOH ( 9a ), and [Cu 2 (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)