New nickel catalyst broadens aryl bromide coupling chemistry

A redesigned nickel-catalysis strategy has expanded the range of aryl bromides that can be joined to heteroatom-containing partners, while sharply reducing the amount of metal catalyst required. The work, reported by Nature Catalysis, combines a purpose-designed ligand with a non-nucleophilic base and visible light to activate nickel under reaction conditions.

The method links electron-rich aryl bromides with nucleophiles based on nitrogen, oxygen, sulfur and phosphorus. It operates with nickel loadings as low as 100 parts per million, and the researchers report that it remains effective with nucleophiles carrying substantial steric congestion. The chemistry has also been demonstrated on a gram scale and used for late-stage modification of complex molecules.

Why these bonds matter

Carbon–heteroatom bonds are a recurring feature of compounds made for practical use. They are important in the preparation of pharmaceuticals, agricultural chemicals and materials, making efficient ways to construct them a central goal of synthetic chemistry.

One established route relies on palladium catalysts. These systems move between palladium oxidation states during the catalytic cycle, but their performance depends heavily on the ligand attached to the metal. The ligand must help manage two competing stages: oxidative addition, in which the catalyst engages the aryl halide, and reductive elimination, in which the new carbon–heteroatom bond is formed.

Balancing those steps often means adjusting the ligand for the particular substrates involved. As a result, a catalyst arrangement that works well for one coupling can require further optimization when the reaction partners change. The need for such substrate-specific tuning is one limitation of palladium-based approaches.

Nickel’s promise and its obstacle

Nickel offers another pathway through a catalytic cycle involving Ni(I) and Ni(III). In this framework, the bond-forming event is intrinsically favourable, giving nickel a potential advantage over systems in which the final coupling step is more difficult to promote.

That advantage has not, by itself, solved the practical problems of Ni(I)/Ni(III) catalysis. Earlier methods have struggled to carry out oxidative addition efficiently. This weakness narrows the range of aryl halides that can participate, particularly limiting the method’s usefulness across different electronic types of substrate. It has also meant that relatively high catalyst concentrations are needed.

The new study addresses that bottleneck rather than relying only on conditions that favour the final bond-forming step. Its ligand was designed using the reaction mechanism as a guide, with the aim of improving nickel’s oxidative-addition reactivity. According to Nature Catalysis, this change broadens the chemistry to electron-rich aryl bromides, a class of coupling partner that had been restricted by the limitations of earlier Ni(I)/Ni(III) methods.

Light-assisted catalyst activation

The ligand is paired with a base additive that does not act as a nucleophile. In the reported system, visible light helps generate Ni(I) directly from a nickel(II) precatalyst that is stable under ordinary bench conditions. This gives the reaction a practical starting point while still producing the nickel oxidation state needed for the catalytic process.

The combination is important because the two parts address different demands. The ligand improves the catalyst’s ability to enter the cycle through oxidative addition, while the light and base system provide a direct route from the stable nickel(II) precursor to active Ni(I). Together, they allow the reaction to proceed with very small quantities of nickel.

The scope demonstrated in the study includes four types of heteroatom nucleophile: nitrogen-, oxygen-, sulfur- and phosphorus-based partners. The reported tolerance of sterically crowded nucleophiles indicates that the method is not confined to especially small or unhindered reaction components. Its performance on gram-scale synthesis further shows that the approach is not limited to small analytical experiments.

Late-stage functionalization adds another practical dimension. This strategy allows complex molecules to be modified near the end of a synthesis, rather than requiring the desired heteroatom-containing group to be installed at an earlier stage. The result is a nickel-catalysed platform that combines broader aryl bromide reactivity with exceptionally low catalyst loading and several routes to carbon–heteroatom bond formation.