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

Abstract

An homologous series of divinylchalcogenophene‐bridged binuclear ruthenium complexes [{(PMe 3 ) 3 Cl(CO)Ru} 2 (µ‐CH=CH‐C 4 H 2 E‐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 ( d Ru–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.