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

Green Molecular Transformation in Dual Catalysis: Photoredox Activation of Vitamin B12 Using Heterogeneous Photocatalyst

This concept focuses on dual-catalysis using metal complexes and heterogeneous photocatalysts. Vitamin B12 derivatives are sophisticated metal complexes that facilitate enzymatic reactions in the biological systems. The B12 enzymes inspired reactions catalytically proceed in dual-catalyst systems of B12 derivatives and heterogeneous photocatalysts, such as titanium oxide (TiO2) and metal-organic frameworks (MOFs), under light irradiation. The cobalt ions in B12 derivatives are effectively reduced by photoexcited photocatalysts, producing low-valent Co(I) species. The photoinduced nucleophilic Co(I) species react with an alkyl halide to form an organometallic complex with a Co-C bond. The Co-C bond dissociates during photolysis to generate alkyl radicals. Based on this mechanism, dual-catalysis effectively promotes various light-driven organic syntheses and light-driven dehalogenation reactions of toxic alkyl halides. The trends of the dual-catalyst system and recent progress in this field are discussed in this concept.

Effect of Macrocycles on the Photochemical and Electrochemical Properties of Cobalt-Dehydrocorrin Complex: Formation and Investigation of Co(I) Species

Co(II)-pyrocobester (P-Co(II)), a dehydrocorrin complex, was semisynthesized from vitamin B12 (cyanocobalamin), and its photochemical and electrochemical properties were investigated and compared to those of the cobester (C-Co(II)), the cobalt-corrin complex. The UV-vis absorptions of P-Co(II) in CH2Cl2, ascribed to the π-π* transition, were red-shifted compared to those of C-Co(II) due to the π-expansion of the macrocycle in the pyrocobester. The reversible redox couple of P-Co(II) was observed at E1/2 = -0.30 V vs Ag/AgCl in CH3CN, which was assigned to the Co(II)/Co(I) redox couple by UV-vis, ESR, and molecular orbital analysis. This redox couple was positively shifted by 0.28 V compared to that of C-Co(II). This is caused by the high electronegativity of the dehydrocorrin macrocycle, which was estimated by DFT calculations for the free-base ligands. The reactivity of the Co(I)-pyrocobester (P-Co(I)) was evaluated by the reaction with methyl iodide in CV and UV-vis to form a photosensitive Co(III)-CH3 complex (P-Co(III)-CH3). The properties of the excited state of P-Co(I), *Co(I), were also investigated by femtosecond transient absorption (TA) spectroscopy. The lifetime of *Co(I) was estimated to be 29 ps from the kinetic trace at 587 nm. The lifetime of *Co(I) became shorter in the presence of Ar-X, such as iodobenzonitrile (1a), bromobenzonitrile (1b), and chlorobenzonitrile (1c), and the rate constants of electron transfer (ET) between the *Co(I) and Ar-X were determined to be 2.9 × 1011 M-1 s-1, 4.9 × 1010 M-1 s-1, and 1.0 × 1010 M-1 s-1 for 1a, 1b, and 1c, respectively.

The inorganic chemistry of the cobalt corrinoids - an update

The inorganic chemistry of the cobalt corrinoids, derivatives of vitamin B₁₂, is reviewed, with particular emphasis on equilibrium constants for, and kinetics of, their axial ligand substitution reactions. The role the corrin ligand plays in controlling and modifying the properties of the metal ion is emphasised. Other aspects of the chemistry of these compounds, including their structure, corrinoid complexes with metals other than cobalt, the redox chemistry of the cobalt corrinoids and their chemical redox reactions, and their photochemistry are discussed. Their role as catalysts in non-biological reactions and aspects of their organometallic chemistry are briefly mentioned. Particular mention is made of the role that computational methods - and especially DFT calculations - have played in developing our understanding of the inorganic chemistry of these compounds. A brief overview of the biological chemistry of the B₁₂-dependent enzymes is also given for the reader's convenience.

Electrogenerated base-promoted cyclopropanation using alkyl 2-chloroacetates

The electrochemical reduction conditions of the reaction of alkyl 2-chloroacetates in Bu4NBr/DMF using a divided cell equipped with Pt electrodes to produce the corresponding cyclopropane derivatives in moderate yields were discovered. The reaction conditions were optimized, the scope and limitations, as well as scale-up reactions were investigated. The presented method for the electrochemical production of cyclopropane derivatives is an environmentally friendly and easy to perform synthetic procedure.

Cobalamin-Mediated Electrocatalytic Reduction of Ethyl Chloroacetate in Dimethylformamide

The catalytic reduction of ethyl chloroacetate (ECA) by hydroxocobalamin (HOCbl) in dimethylformamide was studied electrochemically and spectroelectrochemically to identify initial steps in the reaction between the electrogenerated Co(I) center of cobalamin (cob(I)alamin) and ECA. Cyclic voltammograms of HOCbl in the presence of ECA show a small increase in current related to reduction of Co(II) to Co(I), and a new peak at more negative potentials related to reduction of an ethyl carboxymethyl-Cbl intermediate. The oxidation state of HOCbl during catalysis was monitored by means of spectroelectrochemical controlled-potential bulk electrolysis. Addition of ECA to electrogenerated cob(I)alamin initially generates the Co(II) form (cob(II)alamin) followed by a gradual formation of an ethyl carboxymethyl-Cbl intermediate. Controlled-potential bulk electrolysis was performed to identify products formed from catalytic reduction of ECA by electrogenerated cob(I)alamin and quantify the number of electrons transferred per molecule of ECA. Product distributions and coulometric results, together with the results of voltammograms and spectroelectrochemical controlled-potential bulk electrolysis, were interpreted to propose a reaction mechanism.