Capturing Elusive Cobaltacycle Intermediates: A Real‐Time Snapshot of the CpCoIII‐Catalyzed Oxidative Alkyne Annulation

• Published in: Angewandte Chemie International Edition 2017-09, Vol.56 (40), p.12137-12141
• Main Authors: Sanjosé‐Orduna, Jesús, Gallego, Daniel, Garcia‐Roca, Alèria, Martin, Eddy, Benet‐Buchholz, Jordi, Pérez‐Temprano, Mónica H.
• Format: Article
• Language: English
• Subjects: Alkynes; Catalysis; Catalysts; Chemical reactions; cobalt catalysis; C−H activation; heterocycles; Intermediates; Metals; Organic chemistry; reaction mechanisms; Scaffolds; Species; structure elucidation; Transition metals
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201704744

Despite Cp*CoIII catalysts having emerged as a very attractive alternative to noble transition metals for the construction of heterocyclic scaffolds through C−H activation, the structure of the reactive species remains uncertain. Herein, we report the identification and unambiguous characterization of two long‐sought cyclometalated Cp*CoIII complexes that have been proposed as key intermediates in C−H functionalization reactions. The addition of MeCN as a stabilizing ligand plays a crucial role, allowing the access to otherwise highly reactive species. Mechanistic investigations demonstrate the intermediacy of these species in oxidative annulations with alkynes, including the direct observation, under catalytic conditions, of a previously elusive post‐migratory insertion seven‐membered cobaltacycle. Cyclic Co complex caught: The first direct observation and full characterization of elusive cobaltacycle species in Cp*CoIII‐catalyzed C−H oxidative alkyne annulation is reported. The exceptional ability of MeCN to stabilize otherwise highly reactive intermediates has paved the way to uncover previously inaccessible mechanistic features of these transformations.