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.

Cobalt Catalyst Determines Regioselectivity in Ring Opening of Epoxides with Aryl Halides

Ring-opening of epoxides furnishing either linear or branched products belongs to the group of classic transformations in organic synthesis. However, the regioselective cross-electrophile coupling of aryl epoxides with aryl halides still represents a key challenge. Herein, we report that the vitamin B₁₂/Ni dual-catalytic system allows for the selective synthesis of linear products under blue-light irradiation, thus complementing methodologies that give access to branched alcohols. Experimental and theoretical studies corroborate the proposed mechanism involving alkylcobalamin as an intermediate in this reaction.

Enhanced photocatalytic activity of a B12-based catalyst co-photosensitized by TiO2 and Ru(ii) towards dechlorination

A novel hybrid photocatalyst denoted as B₁₂-TiO₂-Ru(ii) was prepared by co-immobilizing a B₁₂ derivative and trisbipyridine ruthenium (Ru(bpy)₃ ²⁺) on the surface of a mesoporous anatase TiO₂ microspheres and was characterized by DRS, XRD, SEM and BET et al. By using the hybrid photocatalyst, DDT was completely didechlorinated and a small part of tridechlorinated product was also detected in the presence of TEOA only after 30 min of visible light irradiation. Under simulated sunlight, the hybrid exhibited a significantly enhanced photocatalytic activity for dechlorination compared with B₁₂-TiO₂ under the same condition or itself under visible light irradiation due to the additivity in the contribution of UV and visible part of the sunlight to the electron transfer. In addition, this hybrid catalyst can be easily reused without loss of catalytic efficiency. This is the first report on a B₁₂-based photocatalyst co-sensitized by two photosensitizers with wide spectral response.

Significant enhancement of visible light photocatalytic activity of the hybrid B12-PIL/rGO in the presence of Ru(bpy)32+ for DDT dehalogenation

A new hybrid catalyst, B₁₂-PIL/rGO, was prepared. It exhibited enhanced photocatalytic activity for DDT dechlorination in the presence of Ru(bpy)₃²⁺.

Recent trends in the development of vitamin B12 derivatives for medicinal applications

This Feature Article highlights recent developments in the field of vitamin B12 derivatives for medicinal applications. The following topics are emphasized: (1) the development of aquacorrinoids for cyanide detection and detoxification, (2) the use of vitamin B12 conjugates and (3) antivitamins B12 for therapy and diagnosis, and (4) the design of corrinoids as activators of soluble guanylyl cyclase (sGC).

A polymerized ionic liquid-supported B12 catalyst with a ruthenium trisbipyridine photosensitizer for photocatalytic dechlorination in ionic liquids

A visible light-driven catalytic reaction efficiently proceeded in ionic liquids using a PIL-supported B₁₂ catalyst with a Ru(ii) trisbipyridine photosensitizer.

Bioinspired catalytic reactions with vitamin B12 derivative and photosensitizers

As part of a study directed toward design of good catalytic systems based upon a hydrophobic vitamin B12, heptamethyl cobyrinate perchlorate, we describe the preparation of various nanomaterials using the vitamin B12 derivative and photosensitizers. Examples include vitamin B12-hyperbranched polymers (HBPs), human serum albumin (HSA) containing vitamin B12 derivatives, a vitamin B12-titanium dioxide hybrid catalyst, a vitamin B12-Ru complex combined system, and a vitamin B12-rose bengal combined system. These bioinspired materials have the potential as catalytic systems for the degradation of organic halide pollutants and for molecular transformations via radical intermediates during irradiation by UV or visible light, and offer a variety of applications that are of great interest in terms of green chemistry.

Dechlorination of DDT catalyzed by visible-light-driven system composed of vitamin B12 derivative and Rhodamine B

The visible-light-driven dechlorination of 1,1-bis(4-chlorophenyl)-2,2,2-trichloroethane (DDT) was carried out in the presence of a hydrophobic vitamin B12 , heptamethyl cobyrinate perchlorate and Rhodamine B . DDT was successfully dechlorinated to form 1,1-bis(4-chlorophenyl)-2,2-dichloroethane (DDD) as the mono-dechlorinated product upon visible light irradiation with a tungsten lamp (λ > 440 nm). Upon prolonged visible light irradiation to DDT, DDMU (1-chloro-2,2-bis(4-chlorophenyl)ethylene), DDMS (1-chloro-2,2-bis(4-chlorophenyl)ethane) and DCS (trans-4,4′-dichlorostilbene) were obtained as the di- and tri-dechlorinated products. The use of the photostable organic sensitizer enabled prolonged photocatalysis via a noble-metal-free process. The vitamin B12 derivative was replaced by an imine/oxime-type cobalt complex although the cobalt complex system showed a lower catalytic activity than the B12 derivative system. The dechlorination mechanism in the B12 -Rhodamin B system was investigated by various methods such as UV-vis absorption and fluorescence quenching.