Despite its instability in air, Ni(COD)₂ has remained the most important Ni(0) precatalyst and organometallic precursor since the mid-1990s. The slow uptake of nickel catalysis in industry, which limits the applications of nickel chemistry as a whole, can be partially ascribed to the sensitivity of Ni(COD)₂ to air and heat. Despite this, academia has forged ahead, demonstrating that the base-metal can replace palladium for most applications, even enabling reactivity beyond what is possible with palladium-catalyzed cross-coupling, especially for the formation of bonds with sp³-hybridized carbon centers. To overcome the instability of Ni(COD)₂ and allow the full environmental benefits of Ni-catalysis in enabling unique C–C bond formation reactions to reach large-scale industrial processes, a family of air-stable Ni(0) precursors was developed. These precatalysts offer similar efficacy to Ni(COD)₂ in catalysts, allowing researchers in academia and industry to avoid glovebox work and apply nickel catalysis on large scales. In addition, an electrochemical preparation of these precatalysts was developed, allowing more efficient and safer access to the low-valent nickel complexes.
The environmental benefits of this work are manifold. They enable nickel catalysis to replace palladium catalysis more fully in industry, having the potential to reduce the environmental burden of precious-metal catalysis through source reduction. In addition, the air-stable precatalysts obviate the need for laboratories to rely on inert-atmosphere gloveboxes to store and perform nickel catalysis with Ni(0), reducing energy consumption associated with inert-atmosphere use by 98%. Lastly, coupling electrochemical reduction to the preparation of these precatalysts obviates the need for pyrophoric chemical reductants, eliminating 886 grams of pyrophoric chemicals per mole of nickel precatalyst. The protocol can also be coupled to renewable energy sources for carbon-neutral electroreduction.

Yilin Cao

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