Mechanistic insight into the pyridine enhanced α-selectivity in alkyne hydrothiolation catalysed by quinolinolate–rhodium(i)–N-heterocyclic carbene complexes. Issue 24 (21st November 2016)

• Record Type: Journal Article
• Authors: Palacios, Laura; Di Giuseppe, Andrea; Artigas, María José; Polo, Victor; Lahoz, Fernando J.; Castarlenas, Ricardo; Pérez-Torrente, Jesús J.; Oro, Luis A.
• Is Part Of: Catalysis science & technology. Volume 6:Issue 24(2016)
• Page Start: 8548
• Page End: 8561
• Publication Date: 2016-11-21
• Subjects: Catalysis -- Periodicals; 541.395
• DOI: 10.1039/c6cy01884j
• Languages: English
• ISSNs: 2044-4753

Abstract

Abstract : Highly Markovnikov-selective Rh I –NHC–quinolinolate catalysts in alkyne hydrothiolation are reported. Abstract : Rh I –NHC–olefin complexes bearing a N, O-quinolinolate bidentate ligand have been prepared from [Rh(μ-OH)(NHC)(η 2 -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 η 1 -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.