Vitamin B₁₂ catalysis is inspired by the ultimate chemist Nature, as methylcobalamin and adenosylcobalamin are involved in numerous biocatalytic reactions including isomerization, methylation and dehalogenation.^[1,2] This type of catalysis has been successfully translated into the laboratory and used in a small collection of reactions.^{[2, 3]} The advantage of using vitamin B₁₂ as a catalyst lays in the complete stability of the central cobalt ion, whereas most catalytic reactions require the addition of toxic metals plus complex ligands into a cocktail of reagents, vitamin B₁₂in itself is a package deal. It has also been well documented that the reaction mechanism usually follows a radical pathway, bringing a new dimension to this already interesting field.

Along this line, we have proposed vitamin B₁₂ photochemical activation in bond forming and cleavage reactions.^[4] Our results show that TiO₂ can be utilized in a catalytic system with vitamin B₁₂, allowing for the efficient photocatalytic reduction of Co(III) to Co(I). Under light irradiation vitamin B₁₂ derivative unusually catalyzes a new olefinic sp² C-H alkylation reaction, with diazo reagents as a carbene source, instead of the expected cyclopropanation. Furthermore, we also use challenging acyl radicals in C-C bond forming reactions. Light-induced vitamin B₁₂-catalyzed methods are also suitable for C-O bond cleavage. Our studies showed that reduced cyanocobalamin catalyzes C-O bond cleavage in allyloxyarenes.

These key findings emphasize the unique feature of vitamin B₁₂as a catalyst to achieve something unachievable with other methodologies or to find a greener approach.

1. Banerjee, R. Chemistry and Biochemistry of B₁₂, John Wiley & Sons, Inc, 1999
2. K. ó Proinsias, M. Giedyk, D. Gryko, Chem. Soc. Rev. 2013, 42, 6605-6619.
3. Giedyk, M.; Fedosov, S.; Gryko, D. Chem. Commun. 2014, 50, 4674-4676.
4. a) Shimakoshi, H.; Nishi, M.; Tanaka, A.; Chikama, K.; Hiseada, Y. Chem. Commun. 2011, 47, 6548-6550. b) K. Tahara, Y. Hisaeda, Green Chem. 2011, 13, 558-561. H. Shimakoshi, L. Li, M. Nishi, Y. Hisaeda, Chem. Commun. 2011, 47, 10921-10923.