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Published November 26, 2014 | Supplemental Material + Published
Journal Article Open

Nickel-Catalyzed Negishi Arylations of Propargylic Bromides: A Mechanistic Investigation

Abstract

Although nickel-catalyzed stereoconvergent couplings of racemic alkyl electrophiles are emerging as a powerful tool in organic chemistry, to date there have been no systematic mechanistic studies of such processes. Herein, we examine the pathway for enantioselective Negishi arylations of secondary propargylic bromides, and we provide evidence for an unanticipated radical chain pathway wherein oxidative addition of the C–Br bond occurs through a bimetallic mechanism. In particular, we have crystallographically characterized a diamagnetic arylnickel(II) complex, [(i-Pr-pybox)NiIIPh]BAr^F_4, and furnished support for [(i-Pr-pybox)NiIIPh]^+ being the predominant nickel-containing species formed under the catalyzed conditions as well as a key player in the cross-coupling mechanism. On the other hand, our observations do not require a role for an organonickel(I) intermediate (e.g., (i-Pr-pybox)NiIPh), which has previously been suggested to be an intermediate in nickel-catalyzed cross-couplings, oxidatively adding alkyl electrophiles through a monometallic pathway.

Additional Information

© 2014 American Chemical Society. ACS AuthorChoice - This is an open access article published under an ACS AuthorChoice License, which permits copying and redistribution of the article or any adaptations for non-commercial purposes. Received: August 24, 2014; Published: November 17, 2014. This work was supported by the National Institute of General Medical Sciences of the National Institutes of Health (R01-GM62871 to G.C.F. and Ruth L. Kirschstein National Research Service Award F32-GM105295 to N.D.S.). We thank Trixia M. Buscagan (preliminary results), Dr. Ivory Hills (preliminary results), Dr. Angel J. Di Bilio (EPR), Lawrence M. Henling (X-ray crystallography), Prof. Jonas C. Peters (discussions and equipment), Dr. Christopher Uyeda (electrochemistry), and Dr. David VanderVelde (NMR). We acknowledge the Gordon and Betty Moore Foundation, the Beckman Institute, and the Sanofi–Aventis Bioengineering Research Program at Caltech for their support of the Molecular Observatory at Caltech. The SSRL is supported by the Department of Energy's Office of Biological and Environmental Research as well as by the National Institutes of Health.

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Supplemental Material - ja508718m_si_002.pdf

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Created:
August 20, 2023
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October 18, 2023