Metal complexes electropolymerization

The potentiod5mamically electropolymerized metal complexes exhibit both the typical behavior of the polythiophene structure and the metal complex. The same S5mthetic strategy described by Figure 13.25 was used to prepare the fullerene derivatives shown in Figure 13.27, which are potentially useful for photovoltaic energy conversion. ... 

Bipyridyl,4-methyl-4 -vinyl-electrochemical polymerization, 6,25 electropolymerization, 6,16 Bipyridyls bis(ZV-oxide) metal complexes, 2, 496 metai complexes, 2, 89, 90,93 steric effects, 2, 90 2,2 -Biquinolyl... 

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. 

A number of desirable properties were exhibited in this work, which include ease of monomer synthesis, mild positive electropolymerization potential, polymer stability to continuous potential cycling, and stability to storage under ambient conditions. Unfortunately, the nature of the polymer backbone could not be definitely assigned. Nevertheless, the utility of pendant phenol and aniline groups for anchoring metal complexes to an electrode surface is a method worth further investigation. 

Inclusion of the electroactive species as counter-ion during the electropolymerization of the monomer. Another way to prepare noble metal modified electron-conducting polymers is to incorporate into the film a noble metal complex (e.g., [PtCle] ) as a counter-ion during the electropolymerization process. Then reduction or electroreduction of the metallic salt gives the corresponding metal particles. This procedure usually gives not very active Pt particles, maybe because the... 

With respect to the widely investigated metalloporphyrins for catalytic epoxidation, progress was made in the area of polymer-supported ruthenium porphyrins for asymmetric epoxidation. Manganese-porphyrin complexes attached via peptide linkers to organic polymers showed enhanced selectivity and catalyst stability due to donor atoms in the linker that could coordinate to the metal center. This shows that improvement can be achieved not only by optimization of the polymer or metal complex but also by appropriate choice of the linker. Furthermore, electropolymerization by anodic oxidation of suitable manganese-porphyrin complexes proved to be a promising technique for the preparation of efficient immobilized epoxidation catalysts. 

Electropolymerization represents a useful method to control precisely the deposition of thin films of conducting polymers. These thin films have a wide variety of applications in optical devices [29]. Walder and coworkers showed that photocurrents could be generated using a trilayer thin film. The three different electropolymerized polymers were cleverly prepared from a common precursor, 4-methyl-4 -(2-pyrrolyl-1 -ethyl)-2,2 -bipyridine 7 two were alkylated, diquat derivatives and one was the Ru metal complex of this ligand, which acted as a sensitizer. The appropriate ordering of the triad in terms of their redox potentials led to the maximizing of the photocurrent (Scheme 7.2) [30],... 

Different examples of hydrogenation of organic molecules with conducting polymer modified electrodes have been described rather recently in the literature. Two different kinds of modification have been considered for this application insertion of metallic particles, and functionalization of pyrrole with transition metal complexes leading, after electropolymerization, to active electrodes. 

With transition metal complexes (typically rhodium compounds), it is possible to functionalize pyrrole and to obtain active electrodes for the hydrogenation of ketones. An example showing the behaviour of a film of poly(pyiTole-Rh(lll)bipyridyl) is the reduction of cyclohexanone into cyclohexanol with a chemical yield of 79% [110], This molecular electrode is also suitable for the reduction of water in hydrogen, Electrocatalytic hydrogenation of other ketones, unsaturated ketones or aldehydes, has been studied recently [174-176], These hydrogenation reactions are performed in an aqueous medium and the modified electrodes are obtained after electropolymerization of pyrrole substituted 2,2 -bipy-ridine or 1,10-phenanthroline complexes of Pd(Il) or of Rh(Ill). More precisely, with the Pd(ll) complex... 

The majority of the anionic transition-metal complexes discussed above are electrostatically bound to the charged PPy moiety. An interesting alternative can be found in the work of Bidan et al. [25]. These workers synthesized Cu(dpp)2, which contained two entwined dpp ligands covalently attached to pyrrole units. Electropolymerization of the complex yielded an... 

The number of anionic transition-metal complexes that may be electrochemically incorporated into PPy is limited and depends primarily on the electrochemical stability of the species. In order to maintain its chemical integrity upon incorporation into the polymer, the complex should not undergo irreversible oxidation (at the anode) or reduction (at the cathode) during the electropolymerization of pyrrole. The transition-metal complexes shown in Figures 12.2 and 12.3 satisfy these criteria. The following consists of a review of the work performed within our laboratories at Monash University on PPy containing transition-metal complexes. 

Bipyridyl, 4-methyl-4 -vinyl-electrochemical polymerization, 25 electropolymerization, 16 2,2 -Bisphenol metal complexes color photography, 109 Blastocladiella emersonii cation transport, 559 sporulation... 

QCM coated with thin films of metal complexes of protoporphyrin IX dimethyl ester (M-PPIX) deposited by electropolymerization was used to detect the vapors of triethylamine, acetic acid, ethanol, and toluene [52]. Poly-Ni(PPIX) shows larger sensitivity to toluene due to n-n interaction. 

Electropolymerization of suitable substituted metal complexes (Section 6.3), dendrimers (Section 6.4) and hydrogen-bonded networks (Section 6.5) are also dealt with in this chapter. 

All electrochemically stable metal complexes that are substituted by pyrrole, thiophene, aromatic amino, aromatic phenol and some other groups such as vinyl, are suitable for anodic electropolymerizations from solution (organic solvent or water) in the presence of a conducting salt (counter ions in the oxidized films). 

The polymers obtained are in general cross-linked and therefore insoluble. Therefore an exact structure determination is not possible. The metal complex is not destroyed during the electropolymerization, as can be seen... 

Figure 6-5 lists most of the pyrrole-, thiophene-, amino- and hydroxy-substituted porphyrins employed for electropolymerization and the references. Monomers 49a - k [136-147] are based on synthetic porphyrins and 50a, b on deuteroporphyrin [148-150]. Surprisingly, the electrooxidation of metal complexes of protoporphyrin-DC dimethyl ester, possibly via the vinyl groups, leads to the deposition of electroactive porphyrin films on the electrode surface [151-153],... 

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