Bisphosphine-Ligated Nickel Pre-catalysts in C(sp2)-N Cross-Couplings of Aryl Chlorides: A Comparison of Nickel(I) and Nickel(II)

The influence of ancillary ligand and nickel oxidation state in the nickel-catalyzed C(sp(2))-N cross-coupling of aryl chlorides is examined by use of experimental and DFT methods for the first time, focusing on (L) NiCl and (L) Ni(o-tolyl) Cl pre-catalysts (PAd-DalPhos, L1; dppf, L2). Whereas Ni(II) pre-catalysts generally out-performed Ni(I) species in our study, the viability and in some cases superiority of Ni(I) pre-catalysts in challenging aminations is established. Computational analyses support the viability of Ni(0)/Ni(II) cycles featuring rate-limiting CN reductive elimination, as well as parallel Ni(I)/Ni(III) mechanisms involving rate-limiting C-Cl oxidative addition.