Alain Giraudeau

Synthesis and photocatalytic properties of mixed polyoxometalate-porphyrin copolymers obtained from Anderson-type polyoxomolybdates.

Hybrid polyoxometalate-porphyrin copolymeric films are obtained by the electro-oxidation of zinc octaethylporphyrin (ZnOEP) and zinc 5,15-dipyridinium octaethylporphyrin (5,15-ZnOEP(py)(2)(2+)) in the presence of the polyoxometalate [MnMo(6)O(18){(OCH(2))(3)CNHCO(4-C(5)H(4)N)}(2)](3-) (Py-POM-Py). These films allow the photocatalytic reduction of Ag(I)(2)SO(4) under visible irradiation in air in the presence of propan-2-ol at the 2D interface between water and the copolymeric films. The formation of metallic Ag(0) nanowires and triangular nanosheets is observed.

A First Series of Dimeric Porphyrins Electrochemically Linked with Diphosphonium Bridges

The synthesis of dimeric porphyrins with a diphosphonium bridge in a direct one-pot electrochemical reaction is reported. The variation in the yields of this coupling reaction depends on the conditions of the electrolysis, and was examined mainly with respect to the detected by-products. An interpretation of this selective formation of dimers is proposed. Monomers and trimers were also obtained. These new compounds were characterized by 1H NMR, 31P NMR, UV/Vis spectroscopy and microanalysis. Important excitonic interactions were observed when the two porphyrin chromophores were linked with a short diphosphonium bridge. The NMR-spectroscopic data suggest that isomers are present in solution. Electrochemical data indicate that the two phosphonium groups of the bridge are not electrochemically independent in the zinc dimers.

Electrochemical reduction of dimanganese decacarbonyl and dirhenium decacarbonyl

Abstract The electrochemical reduction of Mn 2 (CO) 10 and Re 2 (CO) 10 at mercury electrodes has been studied in organic solvents by classical polarography, coulometry, chronopotentiometry and cyclic voltammetry. The mechanism is electrochemical—chemical and the kinetic parameters of the electrochemical step are given. The reduction products are identified as clusters of manganese and rhenium carbonyls by ir spectroscopy and proton NMR spectroscopy.

Semiconductor electrodes. 30. Spectral sensitization of the semiconductors titanium oxide (n-TiO2) and tungsten oxide (n-WO3) with metal phthalocyanines

Thin films (100 to 250 A) of several phthalocyanines (MgPc, ZnPc, AlClPc, TiOPc, CoPc, FePc, H/sub 2/Pc) were investigated as sensitizers for photoelectrochemical processes at n-type TiO/sub 2/ and WO/sub 3/ single crystal electrodes in aqueous solution. The sensitized oxidation of several solution species (I/sup -/, Fe(CN)/sub 6//sup 4 -/, hydroquinone, Fe(II)-EDTA) occurred with photocurrents proportional to light intensity and spectral responses characteristic of the metal phthalocyanine (MPc) films. At negative electrode potentials cathodic photocurrents for the reduction of benzoquinone, O/sub 2/, and Fe(III)-EDTA were observed, consistent with the p-type behavior of the phthalocyanines themselves. The photoelectrochemical behavior is rationalized from the energy levels of the semiconductors, solution couples, and MPc. The surface ionization potentials were found to yield better estimates of the phthalocyanine levels than the redox potentials of the MPc couples (measured in N,N-dimethylacetamide solutions).

Influence of organic ligands and fac-mer isomerization on the redox behaviour of Ru(III) chloro complexes

Abstract Ruthenium(III) complexes of the type RuCl3L3 (L3 = (ortho-tolunitrile)3, (meta-tolunitrile)3, (pyridine)3, (ortho-tolunitrile)2CH3CN, (ortho-tolunitrile)2pyridine) were studied on platinum electrodes in organic solvents. The complexes undergo a reversible one-electron reduction near O V/SCE, corresponding to the Ru(II)/Ru(III) couple in all studied solvents. In CH3CN, the complexes are reversibly oxidized into Ru(IV). The fac isomers are more difficult to reduce than the mer isomers. The effect of ligand exchange and of fac-mer isomerization upon the Ru(II)Ru(III) redox potential is analysed, and an electrochemically-enhanced lability is evidenced in fac complexes.

Redox behaviour of triangular platinum–cobalt clusters. Electrochemically induced generation of the tetranuclear cluster [Pt2Co2(µ-Co)3(CO)5(PPh3)2]

The redox behaviour of two trimetallic platinum–cobalt clusters [PtCo2(µ-CO)(CO)6(dppe)](1)[dppe = 1,2-bis(diphenylphosphino)ethane] and [PtCo2(µ-CO)(CO)7(PPh3)](2) was studied on both solid and mercury electrodes in aprotic medium by polarography, cyclic voltammetry, and potentiostatic coulometry. The reduction of the two clusters occurs via a one-electron irreversible step which further results in the release of one [Co(CO)4]– anion per mol of cluster. The cluster [Pt2Co2(µ-CO)3(CO)5(PPh3)2](3) was isolated in good yield from the reduction of (2). Each of the clusters (1) and (2) undergoes two one-electron oxidation steps. The first oxidation step is reversible at high potential scans, whereas the second step leads to electrode passivation. The redox potentials corresponding to the studied reactions are compared with those previously obtained for the linear trimetallic complex [(OC)4Co(PtL2)Co(CO)4](4)(L =cyclo-CNC6H11).

Electroreduction of linear trimetallic complexes: M–Hg–M, (M–Au–M)–, M–PtL2–M [M = Co(CO)4, Fe(CO)3NO, Mn(CO)5, Cr(CO)3(η-C5H5), Mo(CO)3(η-C5H5), or W(CO)3(η-C5H5); L = ButNC or C6H11NC]; unexpected generation of radicals

Cathodic reduction of PtII isocyanide compounds M–PtIIL2–M on platinum and gold electrodes in an aprotic medium leads to unexpected paramagnetic PtI species, whereas under the same conditions M–Hg–M and (M–Au–M)– exhibit predictable metal–metal bond cleavage.

Oxidation of Porphyrins in the Presence of Nucleophiles: From the Synthesis of Multisubstituted Porphyrins to the Electropolymerization of the Macrocycles

Electropolymerization of porphyrins has been initially developed by Macor and Spiro, who have polymerized vinyl-substituted porphyrins, the coupling occurring after the formation of vinyl radicals by electrooxidation (Macor & Spiro, 1983). Afterwards, other methods of electropolymerization have been published, for example from hydroxy-, amino-, pyrrole- or thiophene-substituted porphyrins (Bedioui et al., 1995; Bettelheim et al., 1987; Li et al., 2005). In this context, we have developed an original methodology for the electropolymerization of porphyrins, based on nucleophilic attacks of di-pyridyl compounds directly onto electrooxidized porphyrins. This chapter presents an overview of this new method of electropolymerization.

Cyanoporphyrins. Co-ordinating and electrochemical properties

Successive substitutions in the pyrrole rings of tetraphenylporphyrin by up to four cyano-groups lead to large additive anodic shifts of the redox potentials. These shifts are large than those observed with other electron-withdrawing substituents. The stoicheiometry and stability of the complexes formed from metallotetracycanoporphyrins (Cu, Ni, Ag) and nitrogenous bases (pyridine, piperidine) are determined. A novel five-co-ordinate silver(II) porphyrin is reported.

Phenanthroline-assisted metallation of a porphyrin: copper and silver mixed valence homodinuclear complexes

The complexation of copper(II/I) and silver(II/I) in a phenanthroline capped porphyrin ligand has been studied and shows the formation of mixed valence homodinuclear complexes together with a kinetically enhanced complexation within the porphyrin core.