Michel Troupel

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 ‡  +77 kJ mol −1 ; Δ S ‡  13 J mol −1 K −1 . With substituted aromatic iodides, the rate constants give a linear Hammett relationship with ϱ  +2. The suggested mechanism can be regarded as related to an aromatic nucleophilic substitution with some assitance from halogen—palladium interaction.

Electrosynthesis of carboxylic acids from organic halides and carbon dioxide

Abstract The electrocarboxylation of a large variety of organic halides is achieved in simple and mild conditions in diaphragm-less cells.

Room-temperature ionic liquids as new solvents for organic electrosynthesis. The first examples of direct or nickel-catalysed electroreductive coupling involving organic halides

Direct or Ni-catalysed electroreductive homocouplings of organic halides and couplings of organic halides with activated olefins are efficiently conducted by constant current electrolyses in an undivided cell in room-temperature ionic liquids as the solvent-electrolyte media.

ORGANIC ELECTROREDUCTIVE COUPLING REACTIONS USING TRANSITION METAL COMPLEXES AS CATALYSTS

It is about 20 years since the combination of transition-metal catalysis and electroreduction was shown to be applicable to the coupling of organic molecules. This was followed by a number of fundamental investigations and basic syntheses using various nickel, cobalt, or palladium compounds which can easily be reduced in situ electrochemically to low-valent reactive intermediates. The last decade has been less characterized by reports on new catalytic systems than by the development of new synthetic applications. The aim of this review is to show that the electrochemical processes described here offer valuable advantages in organic synthesis.

The coupling of organic groups by the electrochemical reduction of organic halides: Catalysis by 2,2′-bipyridinenickel complexes

Abstract The electrochemical reduction of a dilute solution of NiX 2 bipy (bipy = 2,2′-bipyridine) in N -methylpyrrolidone gives the corresponding Ni 0 complex, which undergoes oxidative addition with an excess of an organic halide RX to form RNiX. Decomposition of RNiX gives the dimer R 2 in good yield and nickel(II). The nickel(0) species is regenerated to give an electrocatalytic process. The possible mechanism of these reactions is discussed briefly.

Electrochemical Determination of pKa of N-Bases in Ionic Liquid Media

Two electrochemical techniques have been used to measure the pK(a) of N-bases in several ionic liquids (ILs). The first method corresponds to a potentiometric titration of a strong acid with the N-base using a platinized Pt indicator electrode immersed in the IL solution and maintained under dihydrogen atmosphere via gas bubbling. The second approach involves performing cyclic voltammetry at a platinized Pt electrode in a solution containing both strong acid and the conjugate weak acid of the N-base. Values of pK(a) obtained by one or the other approach are in good agreement with each other. The experimental data clearly demonstrated that acid/base chemistry in ILs is similar to that observed in molecular nonaqueous solvents; i.e., the relative strengths of the bases were in the right order and spaced (ΔpK(a)). It was also observed that the strength of N-bases is highly dependent on the anion of the ionic liquid; this observation indicates that pH-dependent reactions could be controlled by the appropriate choice of anion for bulk ILs or as an added co-ion to bulk IL.

Three-Component Synthesis of α-Branched Amines under Barbier-like Conditions

An array of alpha-branched amines has been prepared by using an expedient three-component Mannich-type reaction among organic halides, aldehyde derivatives, and amines. The experimental procedure, which is characterized by its simplicity, employs zinc dust for the in situ generation of organozinc reagents. We show that this Barbier-like protocol constitutes a useful entry to diarylmethylamines, 1,2-diarylethylamines, alpha- or beta-amino esters, benzylamines, and beta-arylethylamines.

Scale-up of electrocarboxylation reactions with a consumable anode

Efficient carboxylation of various organic halides can be achieved by electroreduction in aprotic solvents under an atmosphere of carbon dioxide when the selected anodic reaction is the electrodissolution of a magnesium electrode. Successful scale-up from 30 ml atmospheric pressure laboratory cells to a 400 l pressurized pilot unit clearly demonstrates the technical feasibility of this new process for large-scale production of valuable carboxylic acids.

Electroreductive coupling of trifluoromethylarenes with electrophiles: synthetic applications

The electroreductive coupling of trifluoromethylarenes with carbon dioxide, acetone, or N,N-dimethylformamide is achieved with good yields by electrolysis in an undivided cell fitted with a sacrificial anode.

Electrosynthesis of aryl-carboxylic acids from chlorobenzene derivatives and carbon dioxide

Abstract The electrocarboxylation of a large variety of chlorobenzenic compounds is achieved in N,N-dimethylformamide by constant current electrolysis between a stainless steel cathode and a sacrificial magnesium anode in a diaphragmless cell. Substituted benzoic acids are obtained in high yield in simle conditions thus avoiding the usual preparation of organometallic intermediates.