title: Isolation of Key Organometallic Aryl-Co(III) Intermediates in Cobalt-Catalyzed C(sp2)-H Functionalizations and New Insights into Alkyne Annulation Reaction Mechanisms.
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.
authors.affiliation: Institut de Química Computacional i Catàlisi (IQCC) and Departament de Química, Universitat de Girona , Campus Montilivi, Girona, E-17071 Catalonia, Spain.
authors.forename: Oriol
authors.initials: O
authors.lastname: Planas
authors.affiliation: Institut de Química Computacional i Catàlisi (IQCC) and Departament de Química, Universitat de Girona , Campus Montilivi, Girona, E-17071 Catalonia, Spain.|Biomolecular Sciences Research Centre, Faculty of Health and Wellbeing, Sheffield Hallam University , City Campus, Sheffield S1 1WB, England.
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Whiteoak
authors.affiliation: Institut de Química Computacional i Catàlisi (IQCC) and Departament de Química, Universitat de Girona , Campus Montilivi, Girona, E-17071 Catalonia, Spain.
authors.forename: Vlad
authors.initials: V
authors.lastname: Martin-Diaconescu
authors.affiliation: Institut de Química Computacional i Catàlisi (IQCC) and Departament de Química, Universitat de Girona , Campus Montilivi, Girona, E-17071 Catalonia, Spain.
authors.forename: Ilaria
authors.initials: I
authors.lastname: Gamba
authors.affiliation: Institut de Química Computacional i Catàlisi (IQCC) and Departament de Química, Universitat de Girona , Campus Montilivi, Girona, E-17071 Catalonia, Spain.
authors.forename: Josep M
authors.initials: JM
authors.lastname: Luis
authors.affiliation: Servei de RMN, Facultat de Ciències, Universitat Autònoma de Barcelona , Campus UAB, Bellaterra, E-08193 Catalonia, Spain.
authors.forename: Teodor
authors.initials: T
authors.lastname: Parella
authors.affiliation: Institut de Química Computacional i Catàlisi (IQCC) and Departament de Química, Universitat de Girona , Campus Montilivi, Girona, E-17071 Catalonia, Spain.
authors.forename: Anna
authors.initials: A
authors.lastname: Company
authors.affiliation: Institut de Química Computacional i Catàlisi (IQCC) and Departament de Química, Universitat de Girona , Campus Montilivi, Girona, E-17071 Catalonia, Spain.
authors.forename: Xavi
authors.initials: X
authors.lastname: Ribas