Charge Transfer Properties of Benzo[<i>b</i>]thiophene Ferrocenyl Complexes

The synthesis of 2-ferrocenylbenzo­[<i>b</i>]­thiophene, 3-ferrocenylbenzo­[<i>b</i>]­thiophene, 1,1′-bis­(2-indene)­ferrocene, and the two isomers of 1,1′-bis­(2-benzo­[<i>b</i>]­thiophene)­ferrocene was efficiently achieved by using the palladium-catalyzed Negishi C,C cross-coupling reaction of the appropriate bromobenzo­[<i>b</i>]­thiophene derivative with ferrocenylzinc chloride. The accessibility of differently substituted benzo­[<i>b</i>]­thiophenes and a comparison with indene analogues allowed an in-depth investigation on how the geometric modifications and the presence of sulfur affect their physical properties. The molecular structure of 3-ferrocenylbenzo­[<i>b</i>]­thiophene has been determined by X-ray diffraction. Electrochemistry and UV–vis–NIR spectroscopy, in particular the appearance upon oxidation of a charge transfer absorption in the NIR region, are rationalized through quantum chemistry calculations and in the framework of the Hush theory