title: Formation of Ruthenium Carbenes bygem-Hydrogen Transfer to Internal Alkynes: Implications for Alkynetrans-Hydrogenation.
abstract: Insights into the mechanism of the unusualtrans-hydrogenation of internal alkynes catalyzed by {Cp*Ru} complexes were gained by para-hydrogen (p-H2) induced polarization (PHIP) transfer NMR spectroscopy. It was found that the productivetrans-reduction competes with a pathway in which both H atoms of H2are delivered to a single alkyne C atom of the substrate while the second alkyne C atom is converted into a metal carbene. This "geminalhydrogenation" mode seems unprecedented; it was independently confirmed by the isolation and structural characterization of a ruthenium carbene complex stabilized by secondary inter-ligand interactions. A detailed DFT study shows that thetransalkene and the carbene complex originate from a common metallacyclopropene intermediate. Furthermore, the computational analysis and the PHIP NMR data concur in that the metal carbene is the major gateway to olefin isomerization and over-reduction, which frequently interfere with regular alkynetrans-hydrogenation.
authors.affiliation: Max-Planck-Institut für Kohlenforschung, 45470 Mülheim/Ruhr (Germany).
authors.forename: Markus
authors.initials: M
authors.lastname: Leutzsch
authors.affiliation: Max-Planck-Institut für Kohlenforschung, 45470 Mülheim/Ruhr (Germany).
authors.forename: Larry M
authors.initials: LM
authors.lastname: Wolf
authors.affiliation: Max-Planck-Institut für Kohlenforschung, 45470 Mülheim/Ruhr (Germany).
authors.forename: Puneet
authors.initials: P
authors.lastname: Gupta
authors.affiliation: Max-Planck-Institut für Kohlenforschung, 45470 Mülheim/Ruhr (Germany).
authors.forename: Michael
authors.initials: M
authors.lastname: Fuchs
authors.affiliation: Max-Planck-Institut für Kohlenforschung, 45470 Mülheim/Ruhr (Germany).
authors.forename: Walter
authors.initials: W
authors.lastname: Thiel
authors.affiliation: Max-Planck-Institut für Kohlenforschung, 45470 Mülheim/Ruhr (Germany).
authors.forename: Christophe
authors.initials: C
authors.lastname: Farès
authors.affiliation: Max-Planck-Institut für Kohlenforschung, 45470 Mülheim/Ruhr (Germany).
authors.forename: Alois
authors.initials: A
authors.lastname: Fürstner
keywords: Alkine; Carbene; Dichtefunktionalrechnungen; Hydrierungen; NMR‐Spektroskopie; Ruthenium