Spectroscopic properties and electronic structures of 17-electron half-sandwich ruthenium acetylide complexes, [Ru(CCAr)(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(CCAr)(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(CCAr)(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(CCC14H9)(L2)Cp′]+ suggests compounds containing this moiety should be described as metal-stabilised anthryl radical cations.

Graphical abstractOne electron oxidation of [Ru(CCAr)(dppe)Cp∗] affords radical cations, observable by spectroelectrochemical methods. The NIR bands observed are generally attributed to transitions between orbitals which offer significant metal and ethynyl character. In the case of 9-ethynylanthracene derivatives the large anthracene character of the frontier orbitals prompts description as an anthryl radical.Figure optionsDownload full-size imageDownload as PowerPoint slide