Nickel catalysts in Sonogashira coupling reactions.

Nickel has emerged as a desirable substitute for palladium in Sonogashira coupling reactions due to its abundance, less toxicity and high catalytic activity. Ni complexes have been developed to catalyse C(sp)-C(sp) and C(sp)-C(sp) Sonogashira couplings that find applications in the synthesis and modifications of biologically relevant molecules. This review focuses on the catalytic potential and mechanistic details of various Ni complexes employed in the Sonogashira coupling. These include homogeneous catalytic systems with Ni-phosphorus and Ni-nitrogen catalysts, ligand-free catalysts, and carbonylative coupling strategies. Various heterogeneous catalytic systems using supported Ni complexes, Ni nanoparticles and Pd-Ni bimetallic catalysts have also been discussed. This is the first review reported so far dealing exclusively with Ni-catalysed Sonogashira coupling reactions. This review illustrates the current strategies and potential of Ni-catalysed Sonogashira coupling reactions in both homogeneous and heterogeneous systems, and covers the literature up to 2020.