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

A small series of half-sandwich bis(phosphine) ruthenium acetylide complexes [Ru(C CC6H4C CSiMe3) (L-2)Cp'] and [Ru(C=CC6H4C=CC6H4R-4)(L-2)Cp'] (R = OMe, Me, CO2Me, NO2; L-2 = (PPh3)(2), Cp' = Cp; L-2 = 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(C CC6H4C CC6H4OMe-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 'RuC CC6H4' 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. (C) 2011 Elsevier B. V. All rights reserved.