Spectroscopic properties and electronic structures of 17-electron half-sandwich ruthenium acetylide complexes, [Ru(Ctriple bond; length of mdashCAr)(L2)Cp′]+ (Ar = phenyl, p-tolyl, 1-naphthyl, 9-anthryl; L2 = (PPh3)2, Cp′ = Cp; L2 = dppe; Cp′ = Cp∗)

A series of half-sandwich bis(phosphine) ruthenium acetylide complexes [Ru(Ctriple bond; length of mdashCAr)(L2)Cp′] (Ar = phenyl, p-tolyl, 1-naphthyl, 9-anthryl; L2 = (PPh3)2, Cp′ = Cp; L2 = dppe; Cp′ = Cp∗) have been examined using electrochemical and spectroelectrochemical methods. One-electron oxidation of these complexes gave the corresponding radical cations [Ru(Ctriple bond; length of mdashCAr)(L2)Cp′]+. Those cations based on Ru(dppe)Cp∗, or which feature a para-tolyl acetylide substituent, are more chemically robust than examples featuring the Ru(PPh3)2Cp moiety, permitting good quality UV–Vis-NIR and IR spectroscopic data to be obtained using spectroelectrochemical methods. On the basis of TD DFT calculations, the low energy (NIR) absorption bands in the experimental electronic spectra for most of these radical cations are assigned to transitions between the β-HOSO and β-LUSO, both of which have appreciable metal d and ethynyl π character. However, the large contribution from the anthryl moiety to the frontier orbitals of [Ru(Ctriple bond; length of mdashCC14H9)(L2)Cp′]+ suggests compounds containing this moiety should be described as metal-stabilised anthryl radical cations.