Stereo- and Regioselective Alkyne Hydrometallation with Gold(III) Hydrides

The hydroauration of internal and terminal alkynes by gold(III) hydride complexes [(C^N^C)AuH] was found to be mediated by radicals and proceeds by an unexpected binuclear outer‐sphere mechanism to cleanly form trans‐insertion products. Radical precursors such as azobisisobutyronitrile lead to a dra...

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Bibliographic Details
Published in:Angewandte Chemie International Edition 2016-09, Vol.55 (40), p.12321-12324
Main Authors: Pintus, Anna, Rocchigiani, Luca, Fernandez-Cestau, Julio, Budzelaar, Peter H. M., Bochmann, Manfred
Format: Article
Language:English
Subjects:
Alkynes
Azobisisobutyronitrile
Communication
Communications
density functional calculations
Gold
Hydrides
insertion
Isomers
reaction mechanisms
Regioselectivity
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Summary:The hydroauration of internal and terminal alkynes by gold(III) hydride complexes [(C^N^C)AuH] was found to be mediated by radicals and proceeds by an unexpected binuclear outer‐sphere mechanism to cleanly form trans‐insertion products. Radical precursors such as azobisisobutyronitrile lead to a drastic rate enhancement. DFT calculations support the proposed radical mechanism, with very low activation barriers, and rule out mononuclear mechanistic alternatives. These alkyne hydroaurations are highly regio‐ and stereospecific for the formation of Z‐vinyl isomers, with Z/E ratios of >99:1 in most cases. Gold(II) provides a helping hand: Gold(III) pincer complexes overcome their lack of substrate binding sites by participating in a radical‐mediated bimolecular pathway. Gold(III) hydrides react with acetylenes in the presence of a radical source in a kinetically controlled reaction to give trans‐hydroauration products with high regio‐ and stereoselectivity.
ISSN:1433-7851
1521-3773
DOI:10.1002/anie.201607522