For the first time the intermediacy of Pd−O−B linkages, “The Missing Links” have been established in the Suzuki-Miyaura cross-coupling reaction. The use of rapid injection (RI-NMR), low temperature NMR spectroscopy, and reaction kinetic studies have enabled the synthesis and characterization of these highly elusive species. The ability to generate Pd−O−B linkages has provided the opportunity to elucidate aspects of the mechanism for the transfer of the organic moiety from boron to palladium in the cross-coupling process. Specifically, these studies reveal the identity of two distinct Pd−O−B linkages, an activated 8-B-4 and an unactivated 6-B-3 intermediate, both which undergo the transmetalation event leading to cross-coupling product. Two distinct mechanistic pathways have been demonstrated for stoichiometric reactions of Pd-O-B linkages: (1) transmetalation via a boron unactivated 6-B-3 intermediate that dominates in the presence of two ligands per palladium, and (2) transmetalation via a boron activated 8-B-4 intermediate that takes place under conditions of sub-ligated 14-electron palladium complex.

Pre-transmetalation intermediates in the Suzuki-Miyaura reaction revealed: Evidence for “the missing links”

251st National Meeting (2016)

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