Synthesis, electrochemistry and IR spectroelectrochemistry of bisferrocenyl bridged benzene derivates

Two novel biferrocenylcarboxylate benzene derivatives, namely, 1,4-bis(2-Ferrocenecarboxylate) benzene (Fc2B) and 1,4-bis(2-Ferrocenecarboxylate)-2′-methylbenzene (Fc2M), have been synthesized. The as-prepared complexes have been confirmed by IR, 1H NMR and MS. The electron transfer mechanisms of the two compounds and the other three bisferrocenyl bridged benzene complexes, 1,4-disferrocenyl benzene (Fc2P), 1,4-bis(2-ferrocenylvinyl) benzene (Fc2E), and 1,4-bis(2-ferrocenylacetyleneyl) benzene (Fc2Q), have been studied by cyclic voltammetry (CV), in situ difference FT-IR (SNFTIR), and rapid-scan time-resolved FT-IR spectroelectrochemistry (RS-TRS FT-IR). The CV results suggest that the redox formal potentials of the five bridged complexes are depended on their bridged groups and abilities of withdrawing electron. IR absorption peaks arisen from intermediate appearance and disappearance in the oxidation and reduction process of Fc2B, Fc2E, Fc2P and Fc2Q were clearly observed by the in situ rapid-scan or SNFTIR spectroelectrochemistry. The results indicated the redox process of the four bisferrocenyl bridged benzene complexes involved two consecutive one-electron steps. Although the intermediate peak of Fc2M was not observed by in situ FT-IR spectroelectrochemistry, we still thought the redox process of Fc2M could involve two consecutive one-electron steps.