Bioinspired Electrolysis for Green Molecular Transformations of Organic Halides Catalyzed by B12 Complex

Abstract

Naturally-occurring B₁₂ -dependent enzymes catalyze various molecular transformations that are of particular interest from the viewpoint of biological chemistry as well as synthetic organic chemistry. Inspired by the unique property of the B₁₂ -dependent enzymes, various catalytic reactions have been developed using its model complex. Among the B₁₂ model complexes, heptamethyl cobyrinate, synthesized from natural vitamin B₁₂ , is highly soluble in various organic solvents and a redox active cobalt complex with an excellent catalysis in electroorganic synthesis. The electrochemical dechlorination of pollutant organic chlorides, such as DDT, was effectively catalyzed by the B₁₂ complex. Modification of the electrode surface by the sol-gel method to immobilize the B₁₂ complex was also developed. The B₁₂ modified electrodes were effective for the dehalogenation of organic halides with high turnover numbers based on the immobilized B₁₂ complex. Electrolysis of an organic halide catalyzed by the B₁₂ complex provided dechlorinated products under anaerobic conditions, while the electrolysis under aerobic conditions afforded oxygen incorporated products, such as an ester and amide along with dechlorination. Benzotrichloride was transformed into ethylbenzoate or N,N-diethylbenzamide in the presence of ethanol or diethylamine, respectively. This amide formation was further expanded to a unique paired electrolysis. Electrochemical reductions of an alkene and alkyne were also catalyzed by the B₁₂ complex. A cobalt-hydrogen complex should be formed as a bioinspired intermediate. Using the B₁₂ complex, light-assisted electrosynthesis was also developed to save the applied energy.

Keywords: Alkylated complex; Dehalogenation; Enzyme models; Radical reactions; Vitamin B12.