Nickel(I) Aryl Species: Synthesis, Properties, and Catalytic Activity

In this work, Ni­(I) aryl species that are directly relevant to cross-coupling have been synthesized. Transmetalation of (dppf)­NiIX (dppf = 1,1′-bis­(diphenylphosphino)-ferrocene, X = Cl, Br) with aryl Grignard reagents or aryl boronic acids in the presence of base produces Ni­(I) aryl species of the form (dppf)­NiI(Ar) (Ar = Ph, o-tolyl, 2,6-xylyl, 2,4,6-mesityl, 2,4,6-iPr3C6H2). The stability of the Ni­(I) aryl species is inversely correlated to the steric bulk on the aryl ligand. The most unstable Ni­(I) aryl species are the most active precatalysts for Suzuki–Miyaura reactions because they rapidly decompose to generate the active Ni(0) catalyst. This study shows that Ni­(I) aryl species are initially formed in the activation of Ni­(I) halide precatalysts for Suzuki–Miyaura reactions and establishes their stoichiometric and catalytic reactivity profile.