Ionic liquid-mediated Pd-free biaryl synthesis catalysed by in situ generated nickel nanoparticles

Abstract

For the first time, an ionic liquid-mediated nickel-catalysed mild yet efficient protocol has been developed for biaryl synthesis via Suzuki–Miyaura cross coupling (SMC) reactions. The protocol gives access to a wide variety of substituted biaryls with good to excellent yields. The nickel pre-catalyst under the reaction condition is reduced to Ni nanoparticles (Ni NPs). Formation of Ni NPs is confirmed and characterized by PXRD, HRTEM, EDAX and XPS analyses. The XPS analysis reveals that Ni NPs are mostly in the zero oxidation state, which largely explains the efficiency of the catalyst to promote the SMC reaction. The key highlights of the protocol are the use of Ni NPs as a catalyst generated in situ from an inexpensive and easily available precursor, short reaction time, mild reaction conditions and operation in the absence of expensive metals and ligands. This ligand-free methodology also works well for heteroaryl boronic acids.