Identification of a Nitrenoid Reductive Elimination Pathway in Nickel-Catalyzed C–N Cross-Coupling

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.