DUGi

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

http://dugi.udg.edu/item/http:@@@@hdl.handle.net@@2072@@299126

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

American Chemical Society