Syntheses and characterization of Co(III) binuclear complexes with bis(catecholate) ligands containing an acetylene linker

Three binuclear Co(III) complexes with 5,5′-(buta-1,3-diyne-1,4-diyl)bis(3-tert-butylcatechol) (L1), 5,5′-(2,5-dimethoxy-1,4-phenylene)bis(ethyne-2,1-diyl)bis(3-tert-butyl-catechol) (L2) and 5,5′-(4,4′-(buta-1,3-diyne-1,4-diyl)bis(2,5-dimethoxy-4,1-phenylene))bis(ethyne-2,1-diyl)bis(3-tert-butyl-catechol) (L3) have been prepared. The triple bond-containing L1, L2 and L3 ligands were synthesized by a cross-coupling reaction. These complexes were characterized by elemental analyses, electrochemical measurements, 1H NMR and UV–Vis spectra. In [Co2(bpy)4(L1)]2+, electrochemical oxidation of the complexes occurs at the bridges as two closely spaced one-electron couples. UV–Vis spectra reveal that chemical oxidation of [Co2(bpy)4(L1)]2+ using Ag+ occurs as a two-electron process forming [Co2(bpy)4(L1Cat,SQ)]3+ or [Co2(bpy)4(L1SQ,SQ)]4+. On the other hand, [Co2(bpy)4(L2)]2+ and [Co2(bpy)4(L3)]2+ exhibit different oxidation behavior under the same experimental conditions. In this report we discuss the role of the distance between the two metal atoms on the oxidative behavior of binuclear Co(III) complexes.

Graphical abstractThree binuclear Co(III) complexes ([Co2(bpy)4(L1)]2+ (1), [Co2(bpy)4(L2)]2+ (2) and [Co2(bpy)4(L3)]2+ (3)) with bis(catecholate) ligand containing an acetylene linker have been prepared. In (1), new absorption peak appears nearly 613 nm after chemical oxidation. On the other hand, (2) and (3) have no change in UV–Vis spectrum before and after an oxidation.Figure optionsDownload full-size imageDownload as PowerPoint slideResearch highlights► New bis(catechol)s containing an acetylene linker were synthesized using Sonogashira coupling reaction. ► Three Co(III) binuclear complexes with bis(catecholate) ligands were isolated and characterized. ► Chemical and electrochemical oxidation reaction.