Synthesis, Properties, and Electron Transfer Studies of Ferrocenyl Thiophenes

Abstract

Abstract For a series of ferrocenyl thiophenes of type Fe(η5‐C5H4‐(4‐R‐cC4H2S‐3‐yl))(η5‐C5H4‐(C6H3‐3,5‐(CF3)2) [R = H (3a), OMe (4a)], Fe(η5‐C5H4‐(4‐R‐cC4H2S‐3‐yl)(η5‐C5H4‐CHO) [R = H (3b), OMe (4b)], and Fe(η5‐C5H4‐(4‐R‐cC4H2S‐3‐yl)(η5‐C5H4‐C≡N) [R = H (3c), OMe (4c)], the influence of electron‐withdrawing substituents at the ferrocenyl moiety and electron‐donating groups at the thiophene unit on the electronic behavior of 3a–c and 4a–c is reported. The coupling of the ferrocenyl and the thiophene moieties has been realized using the Negishi C,C cross‐coupling reaction protocol. Compounds 3a and 4c were structurally characterized by single‐crystal X‐ray diffraction studies. In electrochemical measurements the ferrocenyl redox potential depends on the particular substitution at the ferrocenyl and the thiophene unit. Moreover, UV/Vis/NIR studies showed ligand‐to‐metal charge transfer (LMCT) interactions, which occur after oxidation and are shifted bathochromically as the donor‐acceptor energy gap decreases. Using different substituents, possessing electron‐withdrawing or donating capabilities, allows adjusting the energy difference between the ferrocenium‐acceptor unit and the donating thiophene system.