Pyridine‐Enhanced Head‐to‐Tail Dimerization of Terminal Alkynes by a Rhodium–N‐Heterocyclic‐Carbene Catalyst |
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| Authors: | Dr Laura Rubio‐Pérez Dipl‐Chem Ramón Azpíroz Dr Andrea Di?Giuseppe Dr Victor Polo Dr Ricardo Castarlenas Prof Jesús J Pérez‐Torrente Prof Luis A Oro |
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| Institution: | 1. Departamento Química Inorgánica, Instituto Síntesis Química y Catálisis Homogénea, Universidad de Zaragoza—CSIC, C/Pedro Cerbuna 12, 50009 Zaragoza (Spain);2. Departamento Química Física e Instituto de Biocomputación y Física de Sistemas Complejos (BIFI), Universidad de Zaragoza, C/Pedro Cerbuna 12, 50009 Zaragoza (Spain);3. Departamento Química Inorgánica, Instituto Síntesis Química y Catálisis Homogénea, Universidad de Zaragoza—CSIC, C/Pedro Cerbuna 12, 50009 Zaragoza (Spain)ARAID Foundation Researcher. |
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| 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 RhI species RhCl(NHC)(η2‐HC?CCH2Ph)(py)] ( 3 ) and RhCl(NHC){η2‐C(tBu)?C(E)CH?CHtBu}(py)] ( 4 ) and the RhIII–hydride–alkynyl species RhClH{? C?CSi(Me)3}(IPr)(py)2] ( 5 ). Computational DFT studies reveal an operational mechanism consisting of sequential alkyne C? H oxidative addition, alkyne insertion, and reductive elimination. A 2,1‐hydrometalation of the alkyne is the more favorable pathway in accordance with a head‐to‐tail selectivity. |
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| Keywords: | alkynes carbenes C?C coupling dimerization rhodium |
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