Ligand redox non-innocent behaviour in ruthenium complexes of ethynyl tolans

A small series of half-sandwich bis(phosphine) ruthenium acetylide complexes [Ru(CCC6H4CCSiMe3)(L2)Cp′] and [Ru(CCC6H4CCC6H4R-4)(L2)Cp′] (R = OMe, Me, CO2Me, NO2; L2 = (PPh3)2, Cp′ = Cp; L2 = dppe; Cp′ = Cp∗) have been synthesised. One-electron oxidations of these complexes gave the corresponding radical cations, which were significantly more chemically stable in the case of the Ru(dppe)Cp∗ derivatives. The representative complex [Ru(CCC6H4CCC6H4OMe-4)(dppe)Cp∗] was further examined by spectroelectrochemical (IR and UV–Vis–NIR) methods. The results of the spectroelectrochemical studies, supported by DFT calculations, indicate that the hole is largely supported by the ‘RuCCC6H4’ moiety in a manner similar to that described previously for simple aryl ethynyl complexes, rather than being more extensively delocalized along the entire conjugated ligand.