Redox chemistry of an ethenyl complex with isolobal CbCo and CpFe fragments

Dyad (η4-C4Ph4)Co(η5-C5H4CHCHFc) (2) containing isolobal iron and cobalt metallocene fragments has been prepared and its structure and spectroelectrochemical properties examined. Both the E and Z isomers have been characterised and their X-ray structures determined. B3LYP/6-31G∗ calculations for 2 show that the HOMO has more electron density on the Fc than on the CbCo(η5-C5H4) fragment whereas the reverse is the case for the LUMO. Both isomers undergo chemically reversible oxidations at the Fc (0.49 and 0.53 V) and CbCo redox centres (0.96 V) but the [2Z]2+ cation isomerises to [2E]2+ concomitant with the second oxidation process. A NIR band at 1290 nm for the [2E]+ cation is assigned to a CbCo(η5-C5H4) → Fc+ charge-transfer.