Chemistry of ruthenium phenolates. Synthesis, characterization and redox properties of a group of salicylaldiminato complexes of ruthenium

Abstract

A group of five mixed ligand ruthenium(II) complexes of general formula [Ru(bpy)(sal-R)₂] (bby= 2, 2′-bipyridine, sal-R = salicylaldiminate anoin) has been synthesizd and characterized. the complexes are diamagnetic (low spin d⁶, S = 0) and show intense MLCT transitions in the visible region in solution. In acetonitrile solution they all show a reversible ruthenium(II)-ruthenium(III) oxidation in the range -0.3 to 0.04 V versus SCE, followed by another reversible ruthenium(III)-ruthenium(IV) oxidation in the range 1.1 to 1.3 V versus SCE. The potential of these two oxidations is sensitive to the nature of the substituent R in the sal-R ligand. A reversible bpy reduction is also observed near -t-1.9 V versus SCE. The five [Ru^III(bpy)(sal-R)₂]⁺ complexes have been synthesized by chemical oxidation of their respective ruthenium(II) precursors by iodine, and isolated as perchlorate salts. These oxidized complexes are paramagnetic (low spin d⁵, S = ½) and show rhombic ESR spectra at 77 K. They show intense LMCT transitions in the visible region in acetonitrile solution, together with weak ligand-field transitions at lower energies. Chemical reduction of these ruthenium(III) complexes by hydrazine gives back the parent ruthenium(II) complexes.