Jean‐François Fauvarque

Kinetics of oxidative addition of zerovalent palladium to aromatic iodides

Abstract The kinetics of oxidative addition of zerovalent palladium to aromatic iodides in tetrahydrofuran in the presence of the ligand triphenylphosphine have been studied by amperometry on the oxidation wave of palladium. The reaction is first order in aromatic iodide and first order in palladium and the rate constant is inversely proportional to the free ligand concentration. The reactive palladium intermediate is assumed to be Pd{P(C 6 H 5 ) 3 } 2 . This assumpion is compatible with the observed activation parameters Δ H ‡ ue5fb +77 kJ mol −1 ; Δ S ‡ ue5fb 13 J mol −1 K −1 . With substituted aromatic iodides, the rate constants give a linear Hammett relationship with ϱ ue5fb +2. The suggested mechanism can be regarded as related to an aromatic nucleophilic substitution with some assitance from halogen—palladium interaction.

Catalyse par des complexs σ-aryl-nickel de l'electroreduction en biaryles des halogenures aromatiques

Abstract In mixed THF/HPMA, electrochemical reduction of NiX 2 L 2 (L = PPh 3 , X = Cl or Br) yields a zerovalent nickel complex which reacts very rapidly with ArX (X = I, Br, Cl) by oxidative addition to give ArNiXL 2 , which also is electroreducible. Thus it is possible to obtain a catalytic electroreduction of ArX which affords mainly biaryls when X = Cl. A mechanism is suggested according the various results especially with a view to explain the loss of catalytic activity. A clear indication of increasing activity is given when aliphatic bromides are added to the solutions.

Optical studies on poly(paraphenylene) thin film prepared by electroreduction

Abstract The results of in situ spectroelectrochemical experiments on thin transparent films of poly( para phenylene) are presented in both oxidation and reduction domains. For reduction, the observed absorptions in the infrared and visible ranges account well for the theoretical predictions. In oxidation, even for a dilute doping level, our data lead to the conclusion that bipolarons are the only gap states involved in the process. Comparisons are established with other published data and theoretical calculations.

Characterization and Doping of Poly(Paraphenylene) Prepared By Catalyzed Electropolymerization

Abstract A new poly(paraphenylene) recently obtained by electropolymerization of dihalobenzene is described in terms of infra-red and UV-visible absorptions, electron paramagnetic resonance, DC conductivity of the pristine material. The first data on ASF5 doping are given. The properties of the electropolymer are compared to those of other poly(paraphenylene) synthesized by chemical methods.

Optical properties of electropolymerized polyparaphenylene

Abstract We present an optical study of polyparaphenylene samples polymerized by electoreduction of 4-4′ dibromo-biphenyl. By elemental analysis, a smaller amount of remaining bromine atoms is found with respect to PPP samples synthesized by the “Yamamoto” procedure. The optical absorption spectrum of these films (or pressed pellets) is composed of a main peak at ≅ 380–390 nm with a shoulder at ≅ 410–420 nm. By comparison with the absorption bands observed for PPP “Kovacic” or PPP “Yamamoto”, these results seem to indicate a dispersion in the chain length of the polymer. In particular, a contribution of longer chain than in PPP “Kovacic” can be estimated. Also, fluorescence spectra show a different behavior. The infrared spectra of these electropolymerized films have been analyzed. A comparison between the ν 1 (800 cm −1 ), {ν 2 (760 cm −1 ) and ν 3 (690 cm −1 )} infrared modes has been made and the results are indicative of an average value of ≅ 14 for the number of phenyl rings in the polymer chain. Raman experiments have been performed with different excitation wavelengths. No frequency dispersion for the 1600 cm −1 Ag Raman mode is observed but, as already reported, different relative intensities for the 1220 cm −1 and 1280 cm −1 modes are detected as a function of λ L . These experimental data agree well with the hypothesis of a dispersion in the chain length of these electropolymerized PPP samples (specially derived from an u.v. excitation wavelength), and particularly of a contribution of rather long chains.

Catalyse par des complexes du nickel l'electrosynthese de 1,1-diarylethane a partir d'halogenures aromatiques et d'ethylene.

Abstract In mixed THF-HMPA, the electrochemical reduction of nickel bromide leads to catalytic nickel very efficient towards the electro-reductive coupling of ethylene with arylhalides yielding 1,1 diarylethane as the main product.

Electrocatalytic assistance by nickel complexes of a coupling reaction between alkenes and aromatic halides leading to substituted olefins

Electrochemical generation of organonickel–phosphine complexes affords a new catalytic route to substituted olefins via the coupling of aromatic halides and alkenes.

Electrochemical Reductive Polycondensation of Dibromoaromatic Derivatives into Poly (1,4 - Phenylene)

Poly (1,4 - phenylene), (PPP), can be prepared by electrochemical reductive polycondensation of 4,4′ - Dibromo biphenyl under controlled potential conditions in polar aprotic medium in presence of Nickel complexes as catalysts. PPP can be prepared in powder form or electrodeposited as thin films over conductive electrodes. The number of phenyl rings in the chain has been checked from infra-red spectra. Physical properties are consistent with the values obtained. During exhaustive electrolysis the highest molecular weight material is formed at the very beginning of the process. This rules out a mechanism of polycondensation which should give the highest molecular weight material at the very end of the process. This suggests a chain mechanism through reactive intermediates.