A ligand-free in situ-generated cobalt nanoparticle catalyst for (Z)-selective transfer semihydrogenation of alkynes

Herein, we developed a simple and efficient approach for the (Z)-selective transfer semihydrogenation of alkynes based on in situ-generated cobalt nanoparticles (CoNPs) and ammonia-borane (NH3.BH3), in which aryl-aryl, aryl-alkyl and terminal alkynes were converted to their (Z)-alkenes in good to excellent yields (72-96%). The heterogeneous and magnetic properties of CoNPs make them easy to separate from the reaction system, and the recovered CoNPs could be reused six times without significant loss of catalytic activity. Moreover, our method also enabled us to prepare combretastatin A-4 (CA-4) at gram scale.