Synthesis and characterization of binuclear Co(II) complexes with bis(salen-type) ligands

Two new, bridged bis(salen-type) ligand precursors, 1,1,3,3-tetrakis(salicylidene-3-iminopropyl)butylenediamine (I) and 1,1,3,3-tetra(salicylideneiminomethyl)propane (IV), were prepared by Schiff base condensation of salicylaldehyde with appropriate tetraamines. Corresponding binuclear Co(II) complexes 1 and 2 were obtained with moderate yields and the complexes were characterized in detail. Structural optimizations of the complexes were carried out at the B3LYP/6-311G∗ level of theory. Dioxygen coordination abilities of 1 and 2 were studied experimentally by UV–Vis spectroscopy and compared with traditional N,N′-ethylenebis(salicylideniminato)Co(II), Co(salen) (3). In addition, catalytic activities of 1 and 2 in comparison with various mononuclear salen-type Co complexes (3–7) were studied in the oxidation of 3,4-dimethoxybenzyl alcohol (veratryl alcohol) in alkaline aqueous solutions.