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.

Two binuclear Co(II) complexes having a bridged bis(salen-type) ligand were synthesized and characterized in detail and their structural optimizations were carried out at the B3LYP/6-311G∗ level of theory. Dioxygen coordination abilities of the complexes were studied by UV–Vis spectroscopy. Catalytic properties of the complexes towards oxidation of 3,4-dimethoxybenzyl alcohol were studied in alkaline aqueous solutions.Figure optionsDownload as PowerPoint slideHighlights
► Synthesis and characterization of two binuclear bis(salen-type) Co(II) complexes.
► Structural modeling shows a tetrahedral geometry around metal centers in one complex.
► The other complex has a nearly square-pyramidal coordination sphere around the metal centers.
► Dioxygen coordination abilities of the complexes were studied by UV–Vis spectroscopy.