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Pyridine‐Enhanced Head‐to‐Tail Dimerization of Terminal Alkynes by a Rhodium–N‐Heterocyclic‐Carbene Catalyst
Author(s) -
RubioPérez Laura,
Azpíroz Ramón,
Di Giuseppe Andrea,
Polo Victor,
Castarlenas Ricardo,
PérezTorrente Jesús J.,
Oro Luis A.
Publication year - 2013
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201302079
Subject(s) - alkyne , carbene , chemoselectivity , rhodium , chemistry , regioselectivity , catalysis , pyridine , medicinal chemistry , ligand (biochemistry) , stereochemistry , combinatorial chemistry , organic chemistry , receptor , biochemistry
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 ‐HCCCH 2 Ph)(py)] ( 3 ) and [RhCl(NHC){η 2 ‐C( t Bu)C( E )CHCH t Bu}(py)] ( 4 ) and the Rh III –hydride–alkynyl species [RhClH{CCSi(Me) 3 }(IPr)(py) 2 ] ( 5 ). Computational DFT studies reveal an operational mechanism consisting of sequential alkyne CH 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.