Electroassisted catalysis of the reductive coupling of 2-bromooctane and methyl vinyl ketone by a binuclear cobalt–salen–iron complex in DMF solution: electrosynthesis and cyclic voltammetry analysis

Abstract

We report in this study the combined use of a CoSalen complex [H 2 Salen \ bis(salicylidene)ethane-1,2-diamine] and an undivided electrochemical cell process in the electroassisted reductive coupling of 2-bromooctane and methyl vinyl ketone with satisfactory results. Correlation between the electroanalytical analysis of the reactivity of CoSalen in the presence of 2-bromooctane and methyl vinyl ketone and the electrosynthesis performed in an undivided electrochemical cell with a sacriÐcial iron anode allows us to suggest that a heterobinuclear CoÈSalenÈFe complex is the e †ective catalyst of the considered reaction. Stability of this intermediate during preparative electrolysis is also discussed.

Cobalt-Salen Catalyzed Electroreductive Alkylation of Activated Olefins

“…Such a crucial role of anodically generated cations has also been reported in other processes related to electroassisted reductions of organohalides catalyzed by nickel complexes [31]. eir occurrence in this reaction was analyzed by cyclic voltammetry and showed the possible formation of a catalytically active Co-Salen-Fe binuclear complex [27]. Indeed, Table 5 recapitulates the comparative analysis of the significant results obtained for reactions carried out with CoSalen, in various conditions, by using either a double compartment or an undivided electrochemical cell.…”

“…is observation suggests that radical R • resulted from alkyl halide reduction may be involved in the reaction mechanism [27].…”

“…is allowed us to show that the combined use of cobalt-Salen (as catalyst) with the undivided electrochemical cell process offers substantial advantages in the reductive coupling of 2-bromooctane and methyl vinyl ketone (MVK) [27]. We report here a systematic study of some examples of reductive coupling of alkyl halides and activated olefins using cobalt complexes to assess the influence of the experimental parameters (ligand, solvent, temperature, and electrolysis conditions) in order to optimize the yield and to get a better insight into the electroassisted catalytic mechanism.…”

Unexpected stabilization of a simple cobalt(I) salt in acetonitrile at a glassy carbon electrode

“…In the absence of ligand, the cobalt(I) species undergoes a very fast disproportionation reaction leading to the loss of the catalyst via the production of inactive solid cobalt [12]. Although this drawback is not encountered with vitamin B12 or ligands such as bipyridine and salen [13][14][15][16][17][18][19][20][21][22][23][24][25][26], the cobalt(I) species, obtained under these conditions, are too stable to efficiently react with aromatic halides, ArX. The use of pyridine as co-solvent was finally found to be a good compromise except for coupling reactions involving electrophiles.…”

Activation of 1-halonaphthalenes by electrogenerated [CoI-salen]−

“…However, homolytic cleavage of the Co-C bond of [R-Co III -salen] may arise in a second step, resulting in an overall electron transfer process. The related synthetic applications of these complexes mainly concern reductions of R-X to R-H [4,7], reductive dimerizations (R-R) [7], coupling of alkyl halides with olefins [8], cyclisations [9,10] or electrochemical carboxylations of allyl and benzyl halides [11]. With respect to the abundant literature devoted to the activation of alkyl halides, the reactions of [Co I -salen] À with aromatic halides have been poorly investigated.…”