Electronically coupled tetrathiafulvalene electrophores across a non-innocent acetylide-ruthenium bridge
Résumé
The synthesis and structural characterization of trans-[Ru(C≡CMe3TTF)2(dppe)2] (HC≡CMe3TTF = 4-ethynyl-4′,5,5′-trimethyltetrathiafulvalene) are described together with the X-ray crystal structures of the organic pro-ligands. Cyclic voltammetry experiments show sequential oxidation of the neutral compound with five one-electron processes up to the corresponding pentacation, trans-[Ru(III)(C≡CMe3TTF)2(dppe)2]5+, evidencing electronic interactions among the three coupled electrophores, the two TTFs and the Ru(II) center. A strong effect of the supporting electrolyte in dichloromethane was observed on the ΔE values especially between the second and third oxidation steps and between the third and fourth one, when [NBu4][PF6] was substituted for Na[B(C6H4(CF3)2)4]. This indicates the appreciable role ion-pairing interactions play in stabilizing these higher charge states, although solvation factors have been shown to be less significant in this case. The separation of the first two redox events was essentially independent of medium effects, indicating a more significant, inherent intramolecular electronic effect. The combined spectroscopic and computational investigations have evidenced that (i) the organic and the metal-based electroactive sites are strongly electronically coupled and (ii) the bisacetylide-ruthenium linker efficiently mediates electronic coupling between the two tetrathiafulvalenes.