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Pre-transmetalation intermediates in the Suzuki-Miyaura reaction revealed: The missing link

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Science  15 Apr 2016:
Vol. 352, Issue 6283, pp. 329-332
DOI: 10.1126/science.aad6981

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Where Pd and B meet in Suzuki coupling

The Suzuki-Miyaura reaction is widely used to form carbon-carbon bonds. It operates by transferring a carbon center from boron to palladium, although the handoff itself happens too quickly to see. Thomas and Denmark have caught sight of the previously elusive intermediate complexes linking palladium to boron through an intervening oxygen. Using low-temperature nuclear magnetic resonance spectroscopy, they characterized the intermediate structures just before the carbon transfer event.

Science, this issue p. 329

Abstract

Despite the widespread application of Suzuki-Miyaura cross-coupling to forge carbon-carbon bonds, the structure of the reactive intermediates underlying the key transmetalation step from the boron reagent to the palladium catalyst remains uncertain. Here we report the use of low-temperature rapid injection nuclear magnetic resonance spectroscopy and kinetic studies to generate, observe, and characterize these previously elusive complexes. Specifically, this work establishes the identity of three different species containing palladium-oxygen-boron linkages, a tricoordinate boronic acid complex, and two tetracoordinate boronate complexes with 2:1 and 1:1 stoichiometry with respect to palladium. All of these species transfer their boron-bearing aryl groups to a coordinatively unsaturated palladium center in the critical transmetalation event.

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