Nickel precatalysts are potentially a more sustainable alternative to traditional palladium precatalysts for the Suzuki-Miyaura coupling reaction. Currently, there is significant interest in Suzuki-Miyaura coupling reactions involving readily accessible phenolic derivatives such as aryl sulfamates, as the sulfamate moiety can act as a directing group for the prefunctionalization of the aromatic backbone of the electrophile prior to cross-coupling. By testing complexes in the Ni(0), (I), and (II) oxidation states, we report a precatalyst, (dppf)Ni(o-tolyl)(Cl) (dppf = 1,1'-bis(diphenylphosphino)ferrocene), for Suzuki-Miyaura coupling reactions involving aryl sulfamates and boronic acids, which operates at significantly lower catalyst loading and at milder reaction conditions than other reported systems. Mechanistic studies on precatalyst activation and the speciation of nickel during catalysis reveal that Ni(I) species are formed in the catalytic reaction via two different pathways. In both cases, the formation of Ni(I) is detrimental to catalysis, which is proposed to proceed via a Ni(0)/Ni(II) cycle. Our mechanistic investigation provides guidelines for designing even more active nickel catalysts for such difficult reactions.

Mechanistic study of an improved nickel precatalyst for the Suzuki-Miyaura reaction of aryl sulfamates: Understanding the role of nickel(I) species

253rd National Meeting (2017)

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