Charge Transfer Properties of Benzo[b]thiophene Ferrocenyl Complexes

Abstract

The synthesis of 2-ferrocenylbenzo[b]-thiophene, 3-ferrocenylbenzo[b]thiophene, 1,1-bis(2-indene)-ferrocene, and the two isomers of 1,1'-bis(2-benzo[b]-thiophene)ferrocene was efficiently achieved by using the palladium-catalyzed Negishi C,C cross-coupling reaction of the appropriate bromobenzo[b]thiophene derivative with ferrocenylzinc chloride. The accessibility of differently substituted benzo[b]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[b]-(t)hiophene 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

Mononuclear piano-stool iron 2-ethynylbenzo[b]thiophene complex: crystal structure and reversible oxidation studied by spectro-electrochemical and DFT methods

“…Both 1 and 2 exhibit strong, presumably π-π* absorption in the UV spectral region, with maxima at 387 nm and 303 nm, respectively. In addition, 2 features a weak MLCT absorption at 457 nm [9]. The oxidation to monocations 1 + and 2 + results in the appearance of a broad band at 788 nm for 1 + and 942 nm for 2 + (table 4).…”

“…A subsequent straightforward three-step procedure gave 1 in high yield. Complex 2 was synthesized by the classical palladium-catalyzed Negishi C-C cross-coupling reaction, following a slightly modified procedure to that reported in the literature [9]. Complex 1 was characterized by 1 H NMR spectroscopy (Supporting Information, figure S1), elemental analysis and single crystal X-ray diffraction.…”

“…The E 1/2 value determined for 1 is lower by 0.56 V compared to 2 (table 3). The HOMO of 2 has been shown to reside 74% on Fe [9] with the withdrawing effect of the benzo[b]thiophene-2-yl substituent increasing the potential of the ferrocene oxidation. In contrast, the HOMO of 1 is strongly delocalized over the π-conjugated Fe-ethynyl-benzothiophene backbone (see the Crystallography and DFT sections for support).…”

“…Oligonuclear organometallic complexes featuring carbon-rich molecular bridges as linkers or components of redox-active centers have served as attractive objects in the field of molecular electronic devices by virtue of their versatile redox and magnetic properties [1][2][3][4][5][6][7][8][9]. In particular, redox-active iron derivatives linked to aromatic and heteroaromatic rings have served as suitable models in studies of electronic communication between metallic termini and screening of molecular wires [10][11][12][13][14].…”

“…We describe herein the synthesis and molecular structure of 1 with benzo[b]thiophene-2-yl linked to the Cp*(dppe)Fe−C≡C− group (chart 1). Along with 1, we also synthesized the reference 2-ferrocenylbenzo[b]thiophene complex (2) to assess the impact of the ethynylene linker on the redox and bonding properties; meantime, 2 has been reported in the literature [9]. The anodic behavior of 1 was investigated in situ by cyclic voltammetry and spectroelectrochemical methods in the UV-vis-NIR and IR spectral regions.…”