A critically important process in catalysis is the formation of an active catalyst from the combination of a metal precursor and a ligand, as the efficacy of this reaction governs the amount of active catalyst. This Review is a comprehensive overview of reactions catalyzed by nickel and an added bidentate phosphine, focusing on the steps transforming the combination of precatalyst and ligand into an active catalyst and the potential effects of this transformation on nickel catalysis. Reactions covered include common cross-coupling reactions, such as Suzuki, Heck, Kumada, and Negishi couplings, addition reactions, cycloadditions, C−H functionalizations, polymerizations, hydrogenations, and reductive couplings, among others. Overall, the most widely used nickel precatalyst with free bidentate phosphines is Ni(cod) 2 , which accounts for ∼50% of the reports surveyed, distantly followed by Ni(acac) 2 and Ni(OAc) 2 , which account for ∼10% each. By compiling the reports of these reactions, we have calculated statistics of the usage and efficacy of each ligand with Ni(cod) 2 and other nickel sources. The most common bidentate phosphines are simple, relatively inexpensive ligands, such as DPPE, DCPE, DPPP, and DPPB, along with others with more complex backbones, such as DPPF and Xantphos. The use of expensive chiral phosphines is more scattered, but the most common ligands include BINAP, Me-Duphos, Josiphos, and related analogs.

A comprehensive study of the reactions of chelating phosphines with Ni(cod) 2 to form (phosphine)Ni(cod), (phosphine) 2 Ni, or mixtures thereof is presented. A series of (phosphine)Ni(cod) complexes were isolated and characterized. The structural differences between the (phosphine)Ni(cod) and (phosphine) 2 Ni complexes were examined using Xray crystallography and 1 H and 31 P NMR spectroscopy. In addition, the effects of ring size, rigidity, and bulk of the phosphine backbone on the formation of either (phosphine)Ni(cod) or (phosphine) 2 Ni were investigated. These studies show that the Ni−P bond lengths in both the (phosphine)-Ni(cod) and (phosphine) 2 Ni complexes and the size of the ring formed by the chelating phosphine and Ni are crucial in determining whether or not (phosphine)Ni(cod) complexes can be isolated. Other factors such as π-stacking interactions were found to have marginal influence.