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Isolation of Key Organometallic Aryl-Co(III) Intermediates in Cobalt- Catalyzed C(sp2)−H Functionalizations and New Insights into Alkyne Annulation Reaction Mechanisms

The selective annulation reaction of alkynes with substrates containing inert C-H bonds using cobalt as catalyst is currently a topic attracting significant interest. Unfortunately, the mechanism of this transformation is still relatively poorly understood, with little experimental evidence for intermediates, although an organometallic Co(III) species is generally implicated. Herein, we describe a rare example of the preparation and characterization of benchtop-stable organometallic aryl-Co(III) compounds (NMR, HRMS, XAS, and XRD) prepared through a C(sp2)-H activation, using a model macrocyclic arene substrate. Furthermore, we provide crystallographic evidence of an organometallic aryl-Co(III) intermediate proposed in 8-aminoquinoline-directed Co-catalyzed C-H activation processes. Subsequent insights obtained from the application of our new organometallic aryl-Co(III) compounds in alkyne annulation reactions are also disclosed. Evidence obtained from the resulting regioselectivity of the annulation reactions and DFT studies indicates that a mechanism involving an organometallic aryl-Co(III)-alkynyl intermediate species is preferred for terminal alkynes, in contrast to the generally accepted migratory insertion pathway

We acknowledge financial support from the European Research Council for the Starting Grant Project ERC-2011-StG-277801 to X.R. and from MINECO of Spain for project CTQ2013-43012-P to A.C. and X.R., CTQ2014-52525-P to J.M.L and CTQ2015-64436-P to T.P. We also thank Generalitat de Catalunya for projects 2014SGR862 and 2014SGR931. We thank the MECD of Spain for a FPU PhD grant to O.P. and MINECO for a Ramón y Cajal contract to A.C. X.R. also thanks Generalitat de Catalunya for an ICREA-Acadèmia Award. In addition, the research leading to these results has received funding from the European Community’s Seventh Framework Programme (FP7/2007-2013) under grant agreement no. 312284

© Journal of the American Chemical Society, 2016, vol. 138, núm. 43, p. 14388-14397

American Chemical Society

Manager: Ministerio de Economía y Competitividad (Espanya)
Author: Planas Fàbrega, Oriol
Whiteoak, Christopher J.
Martin-Diaconescu, Vlad
Gamba, Ilaria
Luis Luis, Josep Maria
Parella Coll, Teodor
Company Casadevall, Anna
Ribas Salamaña, Xavi
Date: 2016 October 10
Abstract: The selective annulation reaction of alkynes with substrates containing inert C-H bonds using cobalt as catalyst is currently a topic attracting significant interest. Unfortunately, the mechanism of this transformation is still relatively poorly understood, with little experimental evidence for intermediates, although an organometallic Co(III) species is generally implicated. Herein, we describe a rare example of the preparation and characterization of benchtop-stable organometallic aryl-Co(III) compounds (NMR, HRMS, XAS, and XRD) prepared through a C(sp2)-H activation, using a model macrocyclic arene substrate. Furthermore, we provide crystallographic evidence of an organometallic aryl-Co(III) intermediate proposed in 8-aminoquinoline-directed Co-catalyzed C-H activation processes. Subsequent insights obtained from the application of our new organometallic aryl-Co(III) compounds in alkyne annulation reactions are also disclosed. Evidence obtained from the resulting regioselectivity of the annulation reactions and DFT studies indicates that a mechanism involving an organometallic aryl-Co(III)-alkynyl intermediate species is preferred for terminal alkynes, in contrast to the generally accepted migratory insertion pathway
We acknowledge financial support from the European Research Council for the Starting Grant Project ERC-2011-StG-277801 to X.R. and from MINECO of Spain for project CTQ2013-43012-P to A.C. and X.R., CTQ2014-52525-P to J.M.L and CTQ2015-64436-P to T.P. We also thank Generalitat de Catalunya for projects 2014SGR862 and 2014SGR931. We thank the MECD of Spain for a FPU PhD grant to O.P. and MINECO for a Ramón y Cajal contract to A.C. X.R. also thanks Generalitat de Catalunya for an ICREA-Acadèmia Award. In addition, the research leading to these results has received funding from the European Community’s Seventh Framework Programme (FP7/2007-2013) under grant agreement no. 312284
Format: application/pdf
Citation: 025863
ISSN: 0002-7863 (versió paper)
1520-5126 (versió electrònica)
Document access: http://hdl.handle.net/10256/13704
Language: eng
Publisher: American Chemical Society
Collection: MINECO/PE 2014-2016/CTQ2013-43012-P
MINECO/PN 2011-2015/CTQ2014-52525-P
Reproducció digital del document publicat a: http://dx.doi.org/10.1021/jacs.6b08593
Articles publicats (D-Q)
info:eu-repo/grantAgreement/EC/FP7/277801
Is part of: © Journal of the American Chemical Society, 2016, vol. 138, núm. 43, p. 14388-14397
Rights: Tots els drets reservats
Subject: Alquins
Alkynes
Reaccions químiques regioselectives
Chemical reactions
Title: Isolation of Key Organometallic Aryl-Co(III) Intermediates in Cobalt- Catalyzed C(sp2)−H Functionalizations and New Insights into Alkyne Annulation Reaction Mechanisms
Type: info:eu-repo/semantics/article
Repository: DUGiDocs

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