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

AbstractA mononuclear iron complex with 2-ethynylbenzo[b]thiophene C-coordinated to the (η5-Cp*)(η2-dppe)Fe (Cp* = pentamethylcyclopentadienyl, dppe = 1,2-diphenylphosphinoethane) framework (1) was prepared and characterized by 1H NMR, elemental analysis, and single crystal X-ray diffraction. The redox behavior of 1 was investigated by voltammetric methods and anodic spectroelectrochemistry in the UV–vis-NIR-IR region and compared with reference complexes including 2-ferrocenylbenzo[b]thiophene (2) and the 2-ethynylpyridine derivative of 1. The spin density distribution along the linear molecular backbone in 1+ was analyzed by DFT (BLYP35) and TDDFT calculations of a truncated model complex. The combined experimental and theoretical results revealed an important role of the ethynylene linker in determining the redox properties of this family of complexes and participation of the 2-ethynylbenzo[b]thiophene framework in the largely iron-based anodic electron transfer.