Open AccessInsight into Transmetalation Enables Cobalt-Catalyzed Suzuki–Miyaura Cross Coupling
Author(s) -
Jamie M. Neely,
Máté J. Bezdek,
Paul J. Chirik
Publication year - 2016
Publication title -
acs central science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 4.893
H-Index - 76
eISSN - 2374-7951
pISSN - 2374-7943
DOI - 10.1021/acscentsci.6b00283
Subject(s) - transmetalation , nucleophile , chemistry , cobalt , electrophile , trifluoromethanesulfonate , reactivity (psychology) , aryl , catalysis , combinatorial chemistry , medicinal chemistry , organic chemistry , medicine , alkyl , alternative medicine , pathology
Among the fundamental transformations that comprise a catalytic cycle for cross coupling, transmetalation from the nucleophile to the metal catalyst is perhaps the least understood. Optimizing this elementary step has enabled the first example of a cobalt-catalyzed Suzuki-Miyaura cross coupling between aryl triflate electrophiles and heteroaryl boron nucleophiles. Key to this discovery was the preparation and characterization of a new class of tetrahedral, high-spin bis(phosphino)pyridine cobalt(I) alkoxide and aryloxide complexes, ( iPr PNP)CoOR, and optimizing their reactivity with 2-benzofuranylBPin (Pin = pinacolate). Cobalt compounds with small alkoxide substituents such as R = methyl and ethyl underwent swift transmetalation at 23 °C but also proved kinetically unstable toward β-H elimination. Secondary alkoxides such as R = i Pr or CH(Ph)Me balanced stability and reactivity. Isolation and structural characterization of the product following transmetalation, ( iPr PNP)Co(2-benzofuranyl), established a planar, diamagnetic cobalt(I) complex, demonstrating the high- and low-spin states of cobalt(I) rapidly interconvert during this reaction. The insights from the studies in this elementary step guided selection of appropriate reaction conditions to enable the first examples of cobalt-catalyzed C-C bond formation between neutral boron nucleophiles and aryl triflate electrophiles, and a model for the successful transmetalation reactivity is proposed.