Nickel-Bromide-Catalyzed Suzuki Coupling Reactions

Nickel-Bromide-Catalyzed Suzuki Coupling Reactions

Author: ChemCatChem

The Suzuki coupling reaction is an efficient tool for the construction of C–C bonds. However, it usually requires expensive Pd-based catalysts. The development of ligand-free and, preferably, Pd-free catalytic systems for Suzuki reactions is, thus, an interesting research target.

Akshai Kumar, Indian Institute of Technology Guwahati, Assam, India, and colleagues have found that inexpensive, earth-abundant nickel bromide can be used to catalyze the Suzuki coupling of a variety of aryl halides with different arylboronic acids (example pictured). In addition to NiBr2 as the catalyst, the team used K3PO4 as a base and 1,4-dioxane as the solvent. The reactions were performed at 120 °C.

The reaction shows good functional group tolerance and provides high yields under ambient, ligand-free, and activator-less conditions. The reactivity of the aryl halides follows the order ArArBr ArCl, in accordance with the bond strengths between the carbon and halogen atoms.

Using this approach, valuable new polycyclic aromatic hydrocarbons with interesting photophysical properties have been synthesized via a nickel(II) catalyzed multi-fold Suzuki coupling of tetrabromoanthracene and tetraiodobenzene with arylboronic acids. The team proposes a nickel(0)/nickel(II) catalytic cycle, where an oxidative addition of the aryl halide to nickel(0) is likely to be the rate-determining-step.



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