Hydroxo-rhodium-N-heterocyclic carbene complexes as efficient catalyst precursors for alkyne hydrothiolation

The new Rh-hydroxo dinuclear complexes stabilized by an N-heterocyclic carbene (NHC) ligand of type [Rh(μ-OH)(NHC)(η2-olefin)] 2 (coe, IPr (3), IMes (4); ethylene, IPr (5)) are efficient catalyst precursors for alkyne hydrothiolation under mild conditions, presenting high selectivity toward α-vinyl...

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Bibliographic Details
Authors: Palacios, Laura, Artigas, María José, Polo, Víctor, Lahoz, Fernando J., Castarlenas, Ricardo, Pérez-Torrente, Jesús J., Oro, Luis A.
Format: article
Status:Versión aceptada para publicación
Publication Date:2013
Country:España
Institution:Consejo Superior de Investigaciones Científicas (CSIC)
Repository:DIGITAL.CSIC. Repositorio Institucional del CSIC
OAI Identifier:oai:digital.csic.es:10261/111227
Online Access:http://hdl.handle.net/10261/111227
Access Level:Open access
Keyword:Rhodium
Homogeneous catalysis
N-heterocyclic carbene
DFT calculations
Hydrothiolation
Hydroxides
Description
Summary:The new Rh-hydroxo dinuclear complexes stabilized by an N-heterocyclic carbene (NHC) ligand of type [Rh(μ-OH)(NHC)(η2-olefin)] 2 (coe, IPr (3), IMes (4); ethylene, IPr (5)) are efficient catalyst precursors for alkyne hydrothiolation under mild conditions, presenting high selectivity toward α-vinyl sulfides for a varied set of substrates, which is enhanced by pyridine addition. The structure of complex 3 has been determined by X-ray diffraction analysis. Several intermediates relevant for the catalytic process have been identified, including RhI-thiolato species Rh(SCH2Ph)(IPr)(η2-coe)(py) (6) and Rh(SCH 2Ph)(IPr)(η2-HCî - CCH2Ph)(py) (7), and the RhIII-hydride-dithiolato derivative RhH(SCH 2Ph)2(IPr)(py) (8) as the catalytically active species. Computational DFT studies reveal an operational mechanism consisting of sequential thiol deprotonation by the hydroxo ligand, subsequent S-H oxidative addition, alkyne insertion, and reductive elimination. The insertion step is rate-limiting with a 1,2 thiometalation of the alkyne as the more favorable pathway in accordance with the observed Markovnikov-type selectivity. © 2013 American Chemical Society.

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