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Visible-light-driven organic synthesis is a green and sustainable method for producing fine chemicals and is highly desirable at both laboratory and industrial scales. In this study, we developed a broad-range (including the red region) visible-light-driven carbonylation of CCl 4 , CBr 4 , and CBr 3 F with nucleophiles, such as amines and alcohols, using a B 12 -Mg 2+ /TiO 2 hybrid catalyst. Carbonyl molecules such as ureas, carbamates, carbonate esters, and carbamoyl fluorides were synthesized with high selectivity and efficiency under mild conditions. Diffuse reflectance UV-vis spectroscopy, femtosecond time-resolved diffuse reflectance spectroscopy, and density functional theory calculations revealed the reaction mechanism is a combination of S N 2 and single-electron transfer. This is a rare example of a low-energy, red-light-driven photocatalysis, which has been a highly desired organic reaction in recent years. We believe that this study provides a general platform to access diverse carbonyl molecules and could promote photocatalytic carbonylation reactions on a pilot scale., (© 2024 The Author(s). Chemistry - A European Journal published by Wiley-VCH GmbH.)

This concept focuses on dual-catalysis using metal complexes and heterogeneous photocatalysts. Vitamin B 12 derivatives are sophisticated metal complexes that facilitate enzymatic reactions in the biological systems. The B 12 enzymes inspired reactions catalytically proceed in dual-catalyst systems of B 12 derivatives and heterogeneous photocatalysts, such as titanium oxide (TiO 2 ) and metal-organic frameworks (MOFs), under light irradiation. The cobalt ions in B 12 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., (© 2024 The Authors. ChemPlusChem published by Wiley-VCH GmbH.)

Co(II)-pyrocobester ( P -Co(II) ), a dehydrocorrin complex, was semisynthesized from vitamin B 12 (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 CH 2 Cl 2 , 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 E 1/2 = -0.30 V vs Ag/AgCl in CH 3 CN, 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)-CH 3 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 × 10 11 M -1 s -1 , 4.9 × 10 10 M -1 s -1 , and 1.0 × 10 10 M -1 s -1 for 1a , 1b , and 1c , respectively.

Continuous flow reactors with immobilized catalysts are in great demand in various industries, to achieve easy separation, regeneration, and recycling of catalysts from products. Oxidation of alcohols with 4-amino-TEMPO-immobilized monolith catalyst was investigated in batch and continuous flow systems. The polymer monoliths were prepared by polymerization-induced phase separation using styrene derivatives, and 4-amino-TEMPO was immobilized on the polymer monolith with a flow reaction. The prepared 4-amino-TEMPO-immobilized monoliths showed high permeability, due to their high porosity. In batch oxidation, the reaction rate of 4-amino-TEMPO-immobilized monolith varied with stirring. In flow oxidation, the eluent permeated without clogging, and efficient flow oxidation was possible with residence times of 2-8 min. In the recycling test of the flow oxidation reaction, the catalyst could be used at least six times without catalyst deactivation.

A B 12 complex-BODIPY dyad was synthesized by peripheral modification of cobalamin derivatives. The photophysical properties of the dyad were investigated by UV-vis, PL, and transient absorption spectroscopy. A visible light-driven dechlorination reaction of a trichlorinated organic compound, DDT, was reported. The dyad showed efficient catalysis for dechlorination under N 2 with turnover numbers of over 220 for the reaction. One-pot syntheses of an ester and amide from DDT and benzotrichloride were also achieved using the dyad under air.