A Hybrid Catalyst for Light‐Driven Green Molecular Transformations

Abstract

This Minireview is focused on the development of hybrid catalysts composed of photosensitizers and a metal complex, especially vitamin B12 derivatives. The semiconductor–metal complex composites are effective photocatalysts for molecular transformations due to the synergistic effect between the two components. The design of a B12 complex for the hybridization with TiO2 was simple and straightforward—cobyrinic acid, having seven carboxylic groups derived from naturally occurring B12 is stably immobilized on the TiO2. By using the hybrid catalysts as mimics of B12‐dependent enzymes, light‐driven reactions such as the dechlorination of organic halide pollutants, and radical‐mediated isomerization proceeded catalytically. In addition to the enzyme‐mimicking reactions, bioinspired reactions were also developed with the hybrid catalyst. The B12–TiO2 hybrid catalyst was used for hydrogen evolution and alkene reduction by UV light irradiation, and the cobalt–hydrogen complex (Co–H complex) was considered to be a putative intermediate of the reactions. The multidisciplinary concept for the design of a hybrid catalyst is described in this Minireview.

Learning From Vitamin B12‐Mediated Reactions: Cobalt(III)−Carbon‐Assisted Catalytic C−H Difluoroacylation of (Hetero)Arenes through Controlled‐Potential Electrolysis

“…Cobalt−carbon complexes are among the most studied organometallic bonds . These complexes act as important synthetic intermediates that can be cleaved homolytically by photolysis, electrolysis, or thermolysis to generate Co(II) and carbon‐centered radicals.…”

meso‐Modified Cobalamins: Synthesis, Structure, and Properties

“…We have reported that the treatment of ah ydrophobic vitaminB 12 derivative, heptamethyl dicyanocobyrinate ((CN) 2 Cby(OMe) 7 ), with 65 %n itric acid gives a nitrated derivative of cobalamin in 78 %y ield. [35] Unfortunately,a pplyingt he same conditions for the nitration of 1 results in am ixture of products and only 19 %y ield of the desired (CN)Cbl(10-NO 2 ) (2)( Ta ble 1, entry 1).…”

“…Vitamin B 12 (1;F igure 1) is vital to living organisms because it is involved in aseries of enzymatic reactions (isomerization,dehalogenation, and methyl transfer). [1][2][3] Its catalytic abilities are intrinsically relatedt ot he hexacoordinated cobalt(III)i on chelated by four corrin nitrogen atoms( equatorial ligand), whereas two other ligands( a-, b-) occupy axial positions.…”

“…[1][2][3] Its catalytic abilities are intrinsically relatedt ot he hexacoordinated cobalt(III)i on chelated by four corrin nitrogen atoms( equatorial ligand), whereas two other ligands( a-, b-) occupy axial positions. The aligand,5 ,6-dimethylbenzimidazole, is inherently connected to the corrin ring via af lexible linker.C onversely,arange of moieties, such as ÀCH 3 ,5 -deoxyadenosyl (Ado), H 2 O, and ÀCN, can serve as b-ligands, depending on the role of vitaminB 12 .T he environmentally benign nature of cobalamin inspires researchers to adopt it into various catalytic reactions, including deha-logenation of polychlorinated compounds, dimerization of benzylh alides, alkylation of olefins, cyclopropanation, cyclopropaner ing opening, or deprotection of (allyloxy)arenes. [4][5][6][7][8][9][10][11][12][13][14] All biological functions of vitaminB 12 ,a sw ell as its catalytic properties, involve oxidation or reduction of the central cobalt ion as the main feature.…”

“…On the contrary,i nt he NO derivative, the strength of the CoÀCN bond increases. [32] The impactofthese discoveries not only expands our knowledge of the behavior of vitamin B 12 ,w hich can ultimately provide us with tools to create effective catalysts, but also contributes to the utilization of cobalamin as ad eliveryv ehicle or controlled drug-releases ystem.I nt his line, Zobi et al reported cis-rhenium(II) dicarbonyl-vitamin B 12 ,i nw hich the activei ngredient was strategically placed on the cobalt ion. [33] Various modifications to the B-ring and meso position reveal that the electronic properties of the corrin ring govern the kinetics of CO release.…”