"Discovery of a biological organometallic reaction sequence involving vitamin B12"

Discovery of the methyl-nickel intermediate on acetyl-CoA synthase was the first documented biological example of an alkylnickel species. A useful model has also been described.

A useful review by S.W Ragsdale, M.Kumar, S. Zhao, S.Menon, J.Seravalli, T.Doukov Ed(s): B.Kraeutler, D.Arigoni, B.T.Golding, Bernard T. Vitamin B12 B12-Proteins, Lect. Eur. Symp., 4th (1998), 167-177. Wiley-VCH Verlag

The Nickel corrin metalloenzyme

Nickel(II) corrin, F430

Thus anaerobic bacteria can convert CO and CO2 or lignins and their degradation products to cell carbon by the acetyl-CoA or Wood/Ljungdahl pathway. This pathway also runs in reverse to allow methanogens to make methane from acetic acid. The unique proteins in the pathway are part of a gene cluster containing five genes that encode a methyltransferase (MeTr), a corrinoid iron-sulfur protein (CFeSP), and the bifunctional protein, CO dehydrogenase/acetyl-CoA synthase (CODH/ACS). Recent work has identified the first example of a bioorganometallic reaction sequence that includes methylcobalt, methylnickel, iron-carbonyl, and acetylmetal intermediates.

This review focuses on the mechanisms of two remarkable Me transfer reactions that involve corrinoids. The first is the MeTr catalyzed methylation of the CFeSP by methyltetrahydrofolate. After the methylated CFeSP dissociates from MeTr, it interacts with CODH/ACS where the methyl-Co(III) bond is cleaved to form a novel methyl-Ni intermediate on CODH/ACS.


A Model - Colligation reactions between a nickel(II) macrocycle and alkyl radicals.
D.G.Kelley, J.H.Espenson, A.Bakac, J. Chem. Soc., Chem. Commun. 1991, 546-7.
"The bimolecular reaction between RRSS-NiL2+ (L = 1,4,8,11-tetraazacyclotetradecane) and alkyl radicals (R) forms the organometallic species RNiL(H2O)2+, with rate constants that vary in the order Me >> primary >> secondary in aqueous HClO4 reflecting the decreasing strength of the Ni-C bond."