Pyridine‐Enhanced Head‐to‐Tail Dimerization of Terminal Alkynes by a Rhodium–N‐Heterocyclic‐Carbene Catalyst. Issue 45 (23rd September 2013)

• Record Type: Journal Article
• Authors: Rubio‐Pérez, Laura; Azpíroz, Ramón; Di Giuseppe, Andrea; Polo, Victor; Castarlenas, Ricardo; Pérez‐Torrente, Jesús J.; Oro, Luis A.
• Is Part Of: Chemistry. Volume 19:Issue 45(2013)
• Page Start: 15304
• Page End: 15314
• Publication Date: 2013-09-23
• Subjects: Chemistry -- Periodicals; 540
• DOI: 10.1002/chem.201302079
• Languages: English
• ISSNs: 0947-6539

Abstract

<abstract abstract-type="main" xml:lang="en"> <title>Abstract</title> <p>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)(η²‐HCCCH₂Ph)(py)] (<bold>3</bold>) and [RhCl(NHC){η²‐C(<italic>t</italic>Bu)C(<italic>E</italic>)CHCH<italic>t</italic>Bu}(py)] (<bold>4</bold>) and the Rh^III–hydride–alkynyl species [RhClH{CCSi(Me)₃}(IPr)(py)₂] (<bold>5</bold>). 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.</p> </abstract>