Four side-off compartmental ligands L1-L4 [L 1 = N,N′-ethylenebis(3-formyl-5-methyl-salicylaldimine), L 2 = N,N′-1-methylethylenebis(3-formyl-5-methylsalicylaldimine), L3 = N,N′-1,1-dimethylethylenebis(3-formyl-5- methylsalicylaldimine) and L4= N,N′-cyclohexenebis(3-formyl-5- methylsalicylaldimine)] having two binding sites, N2O2 and O4, have been chosen to synthesize mononuclear and dinuclear manganese(III) complexes with the aim to study their catecholase activity using 3,5-di-tert-butylcatechol (3,5-DTBC) as substrate in the presence of molecular oxygen. In all cases only mononuclear manganese complexes (1-4) were obtained, with manganese coordination taking place at the N2O2 binding site only, irrespective of the amount of manganese salt used. All these complexes have been characterized by routine physico-chemical techniques. Complex MnL2Cl·4H2O (2) has further been structurally characterized by X-ray single crystal structure analysis. Four dinuclear manganese complexes, 5-8, were obtained after condensing the two pending formyl groups on each ligand (L1-L4) with aniline followed by reaction with MnCl2 to put the second Mn atom onto another N2O2 site. The catalytic activity of all complexes 1-8 has been investigated following the oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC) to 3,5-di-tert-butylbenzoquinone (3,5-DTBQ) with molecular oxygen in two different solvents, methanol and acetonitrile. The study reveals that the catalytic activity is influenced by the solvent and to a significant extent by the backbone of the diamine and the behavior seems to be related mainly to steric rather than electronic factors. Experimental data suggest that a correlation, the lower the E1/2 value the higher the catalytic activity, can be drawn between E1/2 and Vmax of the complexes in a particular solvent. The EPR measurements suggest that the catalytic property of the complexes is related to the metal center(s) participation rather than to a radical mechanism. © 2009 The Royal Society of Chemistry.