title: Ruthenium-catalyzed hydration of 1-alkynes to give aldehydes: insight into anti-Markovnikov regiochemistry.
abstract: The mechanism of the selective conversion of 1-alkynes to aldehydes by hydration was investigated by isolating organic and organometallic byproducts, deuterium-labeling experiments, and DFT calculations. The D-labeled acetylenic hydrogen of 1-alkyne was found exclusively in the formyl group of the resulting aldehydes. After the reaction, the presence of metal-coordinated CO was confirmed. All of the experimental results strongly suggest the involvement of a metal-acyl intermediate with the original acetylenic hydrogen also bound to the metal center as a hydride, with the next step being release of aldehyde by reductive elimination. Theoretical analyses suggest that the first step of the catalytic cycle is not oxidative addition of acetylene C [bond] H or tautomerization of eta(2)-alkyne to a vinylidene complex, but rather protonation of the coordinated 1-alkyne at the substituted carbon to form a metal-vinyl intermediate. This cationic intermediate then isomerizes to Ru(IV)-hydride-vinylidene via alpha-hydride migration of the vinyl group to the metal center, followed by attack of the vinylidene alpha-carbon by OH(-) to give the metal-hydride-acyl intermediate.
authors.affiliation: RIKEN, The Institute of Physical and Chemical Research, Wako-shi, Saitama 351-0198, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Tokunaga
authors.forename: T
authors.initials: T
authors.lastname: Suzuki
authors.forename: N
authors.initials: N
authors.lastname: Koga
authors.forename: T
authors.initials: T
authors.lastname: Fukushima
authors.forename: A
authors.initials: A
authors.lastname: Horiuchi
authors.forename: Y
authors.initials: Y
authors.lastname: Wakatsuki