Magnetic chitosan-functionalized cobalt-NHC: Synthesis, characterization and catalytic activity toward Suzuki and Sonogashira cross-coupling reactions of aryl chlorides

Abstract

• Co-NHC@MC is the first example of Cobalt-NHC catalyst catalyzed the reaction of substituted phenylboronic acid and phenlacethylene with derivatives of aryl chlorides. • Co-NHC@MC showed outstanding catalytic activity toward Suzuki and Sonogashira cross coupling reaction. • Co-NHC@MC catalyzed Suzuki and Sonogashira cross coupling reaction without any toxic reducing agent in PEG as green solvent. • Chitosan was used as an accessible, easily and non-toxic modification-support for cobalt catalyst. • Co-NHC@MC is easily recovered and reused for 7 runs for Suzuki and Sonogashira cross coupling reaction. Aryl chlorides are one of the most stable and available electrophiles, however, their coupling with nucleophiles remains a challenge in organic synthesis. Herein, we prepared a Cobalt-NHC (N-Heterocyclic carbene) complex anchored on magnetic chitosan nanoparticles and assayed its catalytic activity for the reactions of substituted phenylboronic acid and also phenlacetylene with derivatives of aryl chlorides. These reactions are of great importance since they are employed for the synthesis of unsymmetrical diarylethynes and biphenyls, which belong to a prime class of building blocks. The synthesized nanocatalyst was found to be highly efficient in Suzuki and Sonogashira coupling in terms of their activity and recyclability in polyethylene glycol (PEG) as a green reaction media under conditions of temperatures (70 and 100 °C) and Co loading (3 and 6 mol%). To the best of our knowledge, this is the first attempt of using cobalt-NHC complex for catalyzing the abovementioned reactions. Moreover, replacing the earth-abundant Cobalt-based catalyst as an alternative to high cost palladium make this approach promising from sustainable chemistry view.