Asymmetric oxidation of vinyl- and ethynyl terthiophene ligands in triruthenium complexes

Abstract

A series of ruthenium(II) complexes [{RuCl(CO)(PMe₃)₃(–CHCH–)}_nX], 1a–1c (1a: n = 3, X = 3,3′′-dimethyl-2,2′:3′,2′′-terthiophene; 1b: n = 2, X = 2,2′-bithiophene; 1c: n = 2, X = 2,3-bis(3-methylthiophen-2-yl)benzothiophene) and [{Cp*(dppe)₂Ru(–CC–)}₃X], 1d (X = 3,3′′-dimethyl-2,2′:3′,2′′-terthiophene), were prepared and characterized by ¹H, ¹³C and ³¹P NMR. Their redox, spectroscopic and bonding properties were studied with a range of spectro-electrochemical methods in combination with density functional theory calculations. The first two anodic steps observed for 1a and 1d are largely localized on the lateral frameworks of the molecular triangle, the direct conjugation between them being precluded due to the photostable open form of the dithienyl ethene moiety. The third anodic step is then mainly localized on the centerpiece of the triangular structure, affecting both bithiophene laterals. The experimental IR and UV-vis-NIR spectroelectrochemical data and, largely, also DFT calculations account for this explanation, being further supported by direct comparison with the anodic behavior of reference diruthenium complexes 1b and 1c.