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Issue 24, 2016
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Mechanistic insight into the pyridine enhanced α-selectivity in alkyne hydrothiolation catalysed by quinolinolate–rhodium(I)–N-heterocyclic carbene complexes

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Abstract

RhI–NHC–olefin complexes bearing a N,O-quinolinolate bidentate ligand have been prepared from [Rh(μ-OH)(NHC)(η2-olefin)]2 precursors (olefin = cyclooctene, ethylene). The disposition of the chelate ligand with regard to the carbene in the square planar derivatives is strongly influenced by the steric hindrance exerted by the coordinated olefin. These complexes efficiently catalyzed the addition of thiophenol to phenylacetylene with good selectivity to α-vinyl sulfides, which can be increased up to 97% by addition of pyridine. Several key intermediates have been detected including the η1-alkenyl species resulting from alkyne insertion into a Rh–H bond. DFT calculations on the mechanism support a hydrometallation pathway that entails the oxidative addition of thiol, 2,1-insertion of the alkyne into the Rh–H bond, and reductive elimination as the rate-determining step. Remarkably, coordination of pyridine to the β-alkenyl intermediate but not to the α-alkenyl, which results in a net stabilization, is the key for the Markovnikov selectivity.

Graphical abstract: Mechanistic insight into the pyridine enhanced α-selectivity in alkyne hydrothiolation catalysed by quinolinolate–rhodium(i)–N-heterocyclic carbene complexes

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Publication details

The article was received on 02 Sep 2016, accepted on 03 Nov 2016 and first published on 04 Nov 2016


Article type: Paper
DOI: 10.1039/C6CY01884J
Citation: Catal. Sci. Technol., 2016,6, 8548-8561

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    Mechanistic insight into the pyridine enhanced α-selectivity in alkyne hydrothiolation catalysed by quinolinolate–rhodium(I)–N-heterocyclic carbene complexes

    L. Palacios, A. Di Giuseppe, M. J. Artigas, V. Polo, F. J. Lahoz, R. Castarlenas, J. J. Pérez-Torrente and L. A. Oro, Catal. Sci. Technol., 2016, 6, 8548
    DOI: 10.1039/C6CY01884J

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