Preparation and redox properties of novel polymerizable pyrrole- and allyl-functionalized cobaltocenium monomers and siloxane-based cobaltocenium polymers

A series of novel cobaltocenium complexes functionalized with electrochemically and chemically polymerizable pyrrole or allyl substituents, [{eta(5)-C5H5}Co(eta(5)-C5H4C(O)NH(CH2)(3)- NC4H4}] PF6(1), [{eta(5)-C5H4C(O)NH(CH2)(3)NC4H4}(2)Co] PF6 (2), [{eta(5)-C5H5} Co(eta(5)-C5H4C(O)NHC6H4NC4H4}]PF6 (3), [(eta(5)-C5H5}Co{eta(5)-C5H4C(O)NHCH2CH=CH2}]PF6 (4), and [(eta(5)-C5H5}Co(eta(5)-C5H4C(O)OCH2CH=CH2}]PF6 (5), have been prepared via condensation reactions. In a similar way, the siloxane-based polymer 6 and the block copolymer 8, in which the amide-linked cobaltocenium moieties are incorporated in the polymer backbone either as a part of the main polymer chain or as pendant side groups, as well as the dimetallic model complex [{eta(5)-C5H5}Co{eta(5)-C5H4C(O)NH(CH2)(3)Si(CH3)(2)}](2)O][PF6] (7), were prepared and characterized. The molecular structure of the pyrrole-containing cobaltocenium 1 has been determined by a single-crystal X-ray diffraction study. Cyclic voltammetric studies show that the stability of the electrogenerated anionic species depends on the solvent and the nature of the cyclopentadienyl substituents. Gold, platinum, and glassy-carbon electrodes have been successfully modified by electrochemical polymerization of the pyrrole-functionalized monomers 1-3, in acetonitrile solutions, resulting in detectable electroactive cobaltocenium polymer films persistently attached to the electrode surfaces. Glassy-carbon electrodes coated with films of the hydrophobic, siloxane-based, cobaltocenium-containing block copolymer 8 show redox activity in aqueous solutions when an ionic surface-active agent is added to the film.