Strong Interaction between Carbonyl and Dioxolene Ligands Caused by Charge Distribution of Ruthenium–Dioxolene Frameworks of Mono- and Dicarbonylruthenium Complexes

Abstract

Abstract Monocarbonylruthenium complexes with a semiquinone ligand, ([Ru(CO)(sq)(L)]n+ (sq = 3,5-di-tert-butyl-1,2-benzosemiquinone, n = 1 or 0, L = 2,2′:6′,2″-terpyridine ([1]+), 2,6-bis(N,N-dimethylaminomethyl)pyridine ([2]+), 2,6-di-2′-pyridylphenyl ([3]0), or 2-(2,2′-bipyridin-6-yl)phenolato ([4]0)), and dicarbonylruthenium complexes with two semiquinone ligands, [Ru(CO2)2(sq)2] ([5]0) and [Ru(CO)2(phsq)2] (phsq = 9,10-phenanthrasemiquinone, [6]0), were synthesized and the structures of [1]+ and [6] were determined by X-ray crystal analysis. Monocarbonyl Ru(II)–dioxolene complexes displayed the ligand localized catecholato/semiquinone and semiquinone/quinone redox couples, and two sets of those redox couples were observed in the dicarbonyl Ru(II)–bis(dioxolene) complexes. Spectroelectrochemical study revealed that the Ru(II)–catecholato and Ru(II)–semiquinone complexes were stable in solutions, while the Ru(II)–quinone complexes underwent fragmentation in solutions. One-electron reduction of the monocarbonyl Ru(II)–semiquinone complexes caused a red shift of the ν(CO) bands in a range of 41 to 56 cm−1, which was substantially larger than those of carbonyl Ru(II)–polypyridyl complexes. Two ν(CO) bands of dicarbonyl Ru(II)–bis(semiquinone) complexes also shifted to lower wavelength in a range of 53 to 99 cm−1 upon two electron reduction of the complexes. The unusually large red shift of ν(CO) bands upon reduction of carbonyl Ru(II)–dioxolene complexes compared with those of Ru(II)–polypyridyl complex is ascribed to a strong electronic interaction between carbonyl and dioxolene ligands.