Vitamin B12 in Photocatalysis - An Underexplored Frontier in Cooperative Catalysis

Abstract

Vitamin B₁₂ (VB₁₂) is a flexible and sustainable catalyst both in nature and the reaction flask, facilitating varied organic transformations of high value to both enzymatic processes and synthetic chemists. Key to this value is the breadth of reactivity it possesses, capable of both ionic, 2 electron chemistry, and radical, 1 electron chemistry. In particular, the ability to generate carbon-centered radical intermediates via photolysis of organocobalt intermediates formed from alkyl electrophiles opens the door to powerful new radical transformations challenging to achieve using classical photoredox or ligand-to-metal charge transfer (LMCT) catalysis. While this unique photocatalytic reactivity of VB₁₂ has been increasingly leveraged in monocatalytic schemes, recent reports have demonstrated VB₁₂ is able to function as the photocatalytic component in cooperative schemes, driving diverse reactivity including remote elimination of alkyl halides, regioselective epoxide arylation, and regioselective epoxide reduction. This concept briefly overviews the enabling photochemical properties of VB₁₂ and recent applications in cooperative catalysis, providing a framework for the continued development of new cooperative catalyst systems using this powerful photoactive complex.

Keywords: Cooperative catalysis; Earth Abundant Elements; Homogeneous catalysis; Photocatalysis; Radicals.

Figure 1.

Photocatalytic activation approaches for cooperative catalysis with opportunities and challenges

Figure 2.

Vitamin B₁₂ structure and general reactivity.

Figure 3.

(A) Vitamin B₁₂-Catalyzed Olefination by dehydroghalogenation with proposed mechanism. (B) Mechanism of AdoCbl-mediated photodetection in bacterial CarH enzyme. (C) Co(II)(salen) co-catalyst enables novel remote elimination through HAT cascade.

Figure 4.

Vitamin B₁₂ photocatalysis works in conjunction with traditional nickel cross coupling to enable epoxide ring opening arylation.^[20]

Figure 5.

Vitamin B₁₂ and Thiol HAT cooperative catalysis enables mild epoxide ring opening hydrogenation under light visible irradiation.