4-Vinylpyridine complexes, electropolymerization

Electropolyraerization is useful and has been successfully applied to 4-vinylpyridine complexes and to 4-methyl-4 -vinyl-2,2 -bipyridyl.52 Vinylferrocene (vide infra) has been polymerized on to platinum, glassy carbon and titanium dioxide electrodes by introduction to a radiofrequency argon plasma discharge. Electropolymerization and plasma polymerization are likely to be of value to produce copolymers on electrode surfaces. 

Electropolymerization of 4-Vinylpyridine Complexes. Investigations of Structural and Electronic Influences on Thin Film Formation. The recent discovery of the reductive polymerization of complexes containing vinylpyridyl ligands (lg), such as Ru -(bpy)2(vpy)22+ has led to the preparation of homogeneous thin layers of very stable electroactive polymers. This method has been extended to 4-vinyl-4 -methyl-2,2 -bipyridine (lg, 21a) and 4-vinyl-l,10-phenanthroline (21b) on both ruthenium and iron. In the following section we discuss our results on thin films derived from the polymerizable ligands BPE and the trans-4 -X-stilbazoles, (4 -X-stilb X - Cl, OMe, CN and H). 

Crayston and coworkers have shown that vinylpyridine complex 10 may be electropolymerized efficiently in DMSO to yield an orange, luminescent film [33,34]. The method is much more controllable than that used in the traditional electropolymerization method for vinylbipyridine [35] and vinylterpyridine complexes [36]. 

Polymer films can also be electropolymerized directly onto the electrode surface. For example, Abruna et al. have shown that vinylpyridine and vinyl-bipyridine complexes of various metal ions can be electropolymerized to yield polymer films on the electrode surface that contain the electroactive metal complex (see Table 13.2) [27]. The electronically conductive polymers (Table 13.2) can also be electrosynthesized from the corresponding monomer. Again, a polymer film that coats the electrode surface is obtained [25]. Electropolymerized films have also been obtained from styrenic, phenolic, and vinyl monomers. 

Such bilayers can conveniently be built up by successive electropolymerization of complexes containing ligands with vinyl substituents, e.g. 4-vinylpyridine or 4-vinyl-4 -methyl-2,2 -bipyridyl. The films may be deposited on metallic or semiconductor electrodes (e.g. Pt, glassy carbon, Sn02, Ti02). More efficient metailation of the films is obtained by polymerization of coordinated ligand than by subsequent metailation of a preformed polymer film. An alternative to discrete films would be a copolymer with distinct redox sites, or a combination of a single polymer film with a copolymer film in a bilayer device. 

One of the more important aspects of complexes of the type cw-[Os(bipy)2(L2)] + (L = vinylpyridine) is then-use as derivatives to form electroactive polymer films. Thus polypyridine films containing redox-active Os centers can be generated by electropolymerization of the coordinated vinylpyridine ligands of the parent complex from homogeneous solution. Importantly, these polypyridyl films contain redox-active Os fragments at each unit. 

The second section of this paper deals with the synthesis of new Ru and Os derivatives of 4-vinylpyridine (vpy) trans-4-stil-bazole (stilb) and trans-1,2-bis-(4-pyridyl)-ethylene (BPE) and their electroinitiated polymerization reactions. The electropolymerization (EP) reactions of the BPE and stilb complexes represent graphic examples of the broad scope of this surface derivatization technique that is available with substituted vinyl-pyridine ligands (6). These studies have provided considerable insight into structural and electronic influences on thin film formation. 

Useful reviews of work done at The University of North Carolina present the evolution from covalent attachment of pyridine and bipyridine ligands to surfaces of electrodes, through physical adsorption, of poly(vinylpyridine) and related polymers, to electropolymerization of metal complexes containing vinylpyridine and vinylbipyridine ligands (33,3 ). 

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