Identification of a Nitrenoid Reductive Elimination Pathway in Nickel-Catalyzed C–N Cross-Coupling
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Whereas the (bisphosphine)Ni-catalyzed C–N cross-coupling of (hetero)aryl (pseudo)halides with NH nucleophiles represents a useful method for the synthesis of (hetero)anilines, our mechanistic understanding of such cross-couplings is incomplete, especially regarding key C–N reductive elimination steps that are often invoked as turnover-limiting. In this combined experimental and computational study, we provide evidence of a bifurcated C–N reductive elimination pathway for cross-couplings of tBuNH2 and (aryl′)SO2NH2 employing (L1)Ni(aryl)Cl as the precatalyst (L1 = PhPAd-DalPhos). In contrast with direct C–N reductive elimination that proceeds from the nickel alkylamido complex (L1)Ni(aryl)(NHtBu), we provide evidence of a previously undocumented base-promoted pathway involving deprotonation of the nickel sulfonamido complex (L1)Ni(aryl)(NHSO2(aryl′)) to give the anionic nickel nitrenoid species [(L1)Ni(aryl)(NSO2(aryl′))]−, from which C–N reductive elimination occurs preferentially.
