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

A synthetic procedure has been developed to prepare new oxazolo-ferrocene l igands. The method, which allows the formation of homobimetallics oxazole-f errocenes 4-7 containing two oxazole rings in the conjugation chain, is bas ed on the aza-Wittig reaction of alpha -azidoacetyl ferrocene 1 with diacyl chlorides and triphenylphosphine. This route has the characteristic of tun ing the size and shape of the spacer which could have aliphatic, aromatic, and heteroaromatic nature. Likewise, the reaction of 1, 1 1-bis(alpha -azid oacetyl) ferrocene 3 with aroyl chlorides in the presence of triphenylphosp hine affords ferrocene ligands 11 linked to two oxazole rings. The stable s olids were thoroughly characterized by spectroscopic means and electrochemi cal methods. Ligands 4-7 showed chemically reversible oxidations with two o ne-electron processes, indicating that the iron centres do not electronical ly communicate with each other. Electrochemical investigations reveal the r espective 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. (C) 2001 Elsevier Science Ltd. All rights reserved.