Synthesis and electrochemical study of novel oxazolo-ferrocene derivatives displaying redox-switchable character

A synthetic procedure has been developed to prepare new oxazolo-ferrocene ligands. The method, which allows the formation of homobimetallics oxazole–ferrocenes 4–7 containing two oxazole rings in the conjugation chain, is based on the aza-Wittig reaction of α-azidoacetyl ferrocene 1 with diacyl chlorides and triphenylphosphine. This route has the characteristic of tuning the size and shape of the spacer which could have aliphatic, aromatic, and heteroaromatic nature. Likewise, the reaction of 1,1′-bis(α-azidoacetyl) ferrocene 3 with aroyl chlorides in the presence of triphenylphosphine affords ferrocene ligands 11 linked to two oxazole rings. The stable solids were thoroughly characterized by spectroscopic means and electrochemical methods. Ligands 4–7 showed chemically reversible oxidations with two one-electron processes, indicating that the iron centres do not electronically communicate with each other. Electrochemical investigations reveal the respective ferrocene–ferrocenium redox couples of the ligands 11 and 14 are perturbed to a more positive potentials upon protonation and co-ordination of Zn(II) guest cation.