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Please use this identifier to cite or link to this item: http://repository.iitr.ac.in/handle/123456789/20731
Title: Half-Sandwich Ruthenium Carbene Complexes Link trans-Hydrogenation and gem-Hydrogenation of Internal Alkynes
Authors: Guthertz A.
Leutzsch M.
Wolf L.M.
Gupta, Puneet
Rummelt S.M.
Goddard R.
Farès C.
Thiel W.
Fürstner A.
Published in: Journal of the American Chemical Society
Abstract: The hydrogenation of internal alkynes with [Cp∗Ru]-based catalysts is distinguished by an unorthodox stereochemical course in that E-alkenes are formed by trans-delivery of the two H atoms of H2. A combined experimental and computational study now provides a comprehensive mechanistic picture: a metallacyclopropene (Ε2-vinyl complex) is primarily formed, which either evolves into the E-alkene via a concerted process or reacts to give a half-sandwich ruthenium carbene; in this case, one of the C atoms of the starting alkyne is converted into a methylene group. This transformation represents a formal gem-hydrogenation of a Ï€-bond, which has hardly any precedent. The barriers for trans-hydrogenation and gem-hydrogenation are similar: whereas DFT predicts a preference for trans-hydrogenation, CCSD(T) finds gem-hydrogenation slightly more facile. The carbene, once formed, will bind a second H2 molecule and evolve to the desired E-alkene, a positional alkene isomer or the corresponding alkane; this associative pathway explains why double bond isomerization and over-reduction compete with trans-hydrogenation. The computed scenario concurs with para-hydrogen-induced polarization transfer (PHIP) NMR data, which confirm direct trans-delivery of H2, the formation of carbene intermediates by gem-hydrogenation, and their evolution into product and side products alike. Propargylic âOR (R = H, Me) groups exert a strong directing and stabilizing effect, such that several carbene intermediates could be isolated and characterized by X-ray diffraction. The gathered information spurred significant preparative advances: specifically, highly selective trans-hydrogenations of propargylic alcohols are reported, which are compatible with many other reducible functional groups. Moreover, the ability to generate metal carbenes by gem-hydrogenation paved the way for noncanonical hydrogenative cyclopropanations, ring expansions, and cycloadditions. © 2018 American Chemical Society.
Citation: Journal of the American Chemical Society, 140(8): 3156-3169
URI: https://doi.org/10.1021/jacs.8b00665
http://repository.iitr.ac.in/handle/123456789/20731
Issue Date: 2018
Publisher: American Chemical Society
Keywords: Alcohols
Hydrocarbons
Isomers
Organic compounds
Ruthenium
Ruthenium compounds
X ray diffraction
Computational studies
Double-bond isomerization
Induced polarization
Propargylic alcohols
Ruthenium carbene complexes
Ruthenium carbenes
Stabilizing effects
Trans hydrogenations
Hydrogenation
alcohol derivative
alkyne derivative
carbenoid
ruthenium derivative
Article
catalysis
chemical analysis
chemical binding
chemical bond
chemical structure
hydrogenation
isolation procedure
isomerization
nuclear magnetic resonance spectroscopy
polarization
prediction
stereochemistry
X ray diffraction
ISSN: 27863
Author Scopus IDs: 57200970078
54909246400
52164768500
57215231630
55195602900
23070140000
8784063900
7101780684
7006374153
Author Affiliations: Guthertz, A., Max-Planck-Institut für Kohlenforschung, Mülheim/Ruhr, 45470, Germany
Leutzsch, M., Max-Planck-Institut für Kohlenforschung, Mülheim/Ruhr, 45470, Germany
Wolf, L.M., Max-Planck-Institut für Kohlenforschung, Mülheim/Ruhr, 45470, Germany
Gupta, P., Max-Planck-Institut für Kohlenforschung, Mülheim/Ruhr, 45470, Germany
Rummelt, S.M., Max-Planck-Institut für Kohlenforschung, Mülheim/Ruhr, 45470, Germany
Goddard, R., Max-Planck-Institut für Kohlenforschung, Mülheim/Ruhr, 45470, Germany
Farès, C., Max-Planck-Institut für Kohlenforschung, Mülheim/Ruhr, 45470, Germany
Thiel, W., Max-Planck-Institut für Kohlenforschung, Mülheim/Ruhr, 45470, Germany
Fürstner, A., Max-Planck-Institut für Kohlenforschung, Mülheim/Ruhr, 45470, Germany
Corresponding Author: Fürstner, A.; Max-Planck-Institut für KohlenforschungGermany; email: fuerstner@kofo.mpg.de
Appears in Collections:Journal Publications [CY]

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