Vinyl-pyrazole as a biomimetic acetaldehyde surrogate

Inspired by the enzyme acetylene hydratase, we investigated the reactivity of acetylene with tungsten( ii ) pyrazole complexes. Our research revealed that the complex [WBr 2 (pz-NHCCH 3 )(CO) 3 ] (pz = 3,5-dimethyl-pyrazolate) facilitates the stochiometric reaction between pzH and acetylene to give N -vinyl-pz. This vinyl compound readily hydrolyzes to acetaldehyde, mirroring the product of acetylene hydration in the enzymatic process. The formation of the vinyl compound likely involves a reactive intermediate complex where acetylene acts as a two-electron donor, in contrast to isolable acetylene complexes that are inert to nucleophilic attack by water. Results suggest an alternative mechanism for the enzyme, including vinylation of a neighboring amino acid by acetylene in the active site prior to hydration. Acetaldehyde formation is mediated by a tungsten pyrazole complex via a vinyl intermediate and subsequent hydrolysis-a rare example of the reactivity of unsubstituted acetylene.