Alkylcobalamins elimination

Simple alkylcobalt complexes (i.e. those without heteroatomic substituents on the alkyl ligand) are also known to undergo eliminations of cobalt(I) species. Thus Grate and Schrauzer [42] have studied the decomposition of unstable, sterically strained secondary alkyl- and cycloalkyl-cobalamins to form olefins and hydridocobalamin in neutral and acidic solution. In this case the formation of hydridocobalamin was inferred from the observation of monodeuteriohydrogen gas when undeuterated alkylcobalamins were decomposed in DCl/DjO, presumably via Eqns. 42 and 43. 

Mechanism of Elimination Reactions of Substituted Alkylcobaloximes and Alkylcobalamins... 

In view of the reversibility of / -elimination reactions in the chemistry of substituted alkylcobalamins and -cobaloximes and the potential biochemical importance of such reactions, we will now discuss the mechanism of these remarkable reactions (9). 

Y = RS , Cl , Br- I-, CN , PBu 3, PPhg, Se , etc.). Higher alkyl-cobalt derivatives also react with strong nucleophiles, but here olefin elimination occurs rather than nucleophilic displacement. The reaction of iV-alkylcobalamins and A -alkyl cobalt derivatives of five different B12 models with mercaptide ions produces thio-ethers, and it has been found that the relative rates of S-alkylation follow a pattern which is typical of Sn2 displacement rather than a free-radical reaction. 

The decomposition of alkylcobalamin by j8-elimination of H, whether by a route analogous to (18) or (20), is impossible in neopentyl and benzyl cobalamins and cobinamides. Schrauzer s group has studied the decomposition, in the absence and presence of O2, of such compounds. The slowness of the reaction under the first conditions points to reactions (14) and (26), equilibrium lying to the left in the former and the latter... 

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