Electronic Structures of Divinylchalcogenophene‐Bridged Biruthenium Complexes: Exploring Trends from O to Te

Abstract

An homologous series of divinylchalcogenophene‐bridged binuclear ruthenium complexes [{(PMe3)3Cl(CO)Ru}2(µ‐CH=CH‐C4H2E‐CH=CH)] (4a–4d, E = O, S, Se, Te) have been synthesised and fully characterised by X‐ray crystallography and various spectroscopic techniques. The single‐crystal X‐ray diffraction results reveal a distinct short/long bond‐length alternation along the polyene‐like hydrocarbon backbone, with geometric constraints imposed by the chalcogenophene leading to an increasing distance between the two metal centres (dRu–Ru) in complexes 4a–4d as the heteroatom in the five‐membered ring is changed from oxygen (9.980 Å in 4a) to tellurium (11.063 Å in 4d). The complexes undergo two sequential one‐electron oxidation processes, the half‐wave potential and separation of which appear to be sensitive to a range of factors, including aromatic stabilisation and re‐organisation energies. Analysis of [4a–4d]n+ (n = 0, 1, 2) by UV/Vis/NIR and IR spectroelectrochemical methods, supported by DFT calculations (n = 0, 1), revealed that the redox character of the complexes is dominated by the polyene‐like backbone with the chalcogenide playing a subtle but influential, structural rather than electronic, role. In the radical cations [4a–4d]+, the charge is rather effectively delocalised over the 10‐atom Ru–[4‐s‐cis‐all‐trans‐(CH=CH)4]–Ru chain, giving rise to a species with spectroscopic properties not dissimilar to oxidised polyaceylene.