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

Abstract

A 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.

Keywords:

• Benzo[b]thiophene
• iron cyclopentadienyl complex
• ethynylene linker
• X-ray crystallography
• spectroelectrochemistry
• density functional theory

Acknowledgements

The authors acknowledge financial support from the Opening Subjects of Hunan Province Key Laboratory of Functional Organometallic Materials (Grant No. GN15K05) and the Scientific Research Foundation of the Hengyang Normal University (Grant No. 14B23). The theoretical calculations and spectroelectrochemistry were conducted in the Department of Chemistry at the Central China Normal University. F.H. thanks the University of Reading for the continued support of the Reading Spectroelectrochemistry laboratory (Project D14-015).