How does vitamin B12 contain an organometallic bond?

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periodic table with group numbers and the s, p, d, and f blocks — organometallic compound The periodic table of the elements, displaying the group numbers and the s, p, d, and f blocks. Elements in the shaded area are the metals of organometallic chemistry.

Vitamin B12 is considered an organometallic compound because it contains at least one direct metal-to-carbon bond, which is the defining characteristic of this class of substances.12

Specifically, in its active coenzyme forms—such as methylcobalamin and 5-deoxyadenosylcobalamin—the vitamin features a central cobalt atom that is bonded directly to a carbon atom. This cobalt-carbon (Co–C) bond qualifies the molecule as an organometallic compound. While organometallic compounds are generally unusual in biological processes, the vitamin B12 coenzyme serves as a notable natural example of this chemistry.34