2013
DOI: 10.1002/chem.201302079
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Pyridine‐Enhanced Head‐to‐Tail Dimerization of Terminal Alkynes by a Rhodium–N‐Heterocyclic‐Carbene Catalyst

Abstract: A general regioselective rhodium-catalyzed head-to-tail dimerization of terminal alkynes is presented. The presence of a pyridine ligand (py) in a Rh-N-heterocyclic-carbene (NHC) catalytic system not only dramatically switches the chemoselectivity from alkyne cyclotrimerization to dimerization but also enhances the catalytic activity. Several intermediates have been detected in the catalytic process, including the π-alkyne-coordinated Rh(I) species [RhCl(NHC)(η(2)-HC≡CCH2Ph)(py)] (3) and [RhCl(NHC){η(2)-C(tBu)… Show more

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Cited by 50 publications
(30 citation statements)
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“…[4] Building on early landmarks, [5] rhodium-based catalysts are of notable contemporary interest. [6][7][8][9] Recent examples bearing anionic pincer ligands,i np articular,s how promising activity and product fidelity.F or instance,Rh(CNC) complex A has been shown to be ahighly selective precatalyst for the production of arange of gem-enynes (1 mol %, 80 8 8C), [6] while Rh(PNP) complex B principally affords E-enynes under similar conditions (1 mol %, 100 8 8C). [7] Although closely related Rh(PNP) and Rh(PCP) systems demonstrate reduced selectivity,they predominantly give mixtures of only gem-and E-enynes.…”
mentioning
confidence: 99%
“…[4] Building on early landmarks, [5] rhodium-based catalysts are of notable contemporary interest. [6][7][8][9] Recent examples bearing anionic pincer ligands,i np articular,s how promising activity and product fidelity.F or instance,Rh(CNC) complex A has been shown to be ahighly selective precatalyst for the production of arange of gem-enynes (1 mol %, 80 8 8C), [6] while Rh(PNP) complex B principally affords E-enynes under similar conditions (1 mol %, 100 8 8C). [7] Although closely related Rh(PNP) and Rh(PCP) systems demonstrate reduced selectivity,they predominantly give mixtures of only gem-and E-enynes.…”
mentioning
confidence: 99%
“…Two main mechanistic pathways are recognized for alkyne dimerization . The first one involves oxidative addition of the C−H bond generating a rhodium‐alkynyl‐hydride complex, followed by coordination of a second alkyne and either insertion of the coordinated alkyne into the M−H bond (hydrometalation) or into the M−C bond (carbometalation) and subsequent reductive elimination to afford the enyne.…”
Section: Resultsmentioning
confidence: 99%
“…A plausible mechanism for the dimerization of alkynes by using complex 2 as catalyst precursor is shown in Scheme . Only the hydrometalation path has been considered because this step is typically lower in energy than the carbometalation …”
Section: Resultsmentioning
confidence: 99%
“…As previously proposed, [7j] the first step of the process is the exchange of the hydride ligand Rh III -H (a) by deuterium from the deuterated solvent (CD 3 OD) to generate an Rh III -D species (b) (Scheme 8). [24] Then, after coordination of the olefin to complex b to give an intermediate species with the ligands in a cis disposition, [25] the orientation of the h 2 -coordinated olefin determines the insertion pathway. A 1,2-insertion into the RhÀD bond gives rise to the linear product c, whereas a 2,1-insertion provides the branched product e. At this point, rotation about the C 1 -C 2 alkyl axis is essential for effective H/D exchange (c!d; e!f).…”
Section: Catalytic Activity Studiesmentioning
confidence: 99%