A simple and efficient in situ generated copper nanocatalyst for stereoselective semihydrogenation of alkynes

Development of a simple, effective, and practical method for ( Z )-selective semihydrogenation of alkynes has been considered necessary for easy-to-access applications at organic laboratory scales. Herein, ( Z )-selective semihydrogenation of alkynes was achieved using a copper nanocatalyst which was generated in situ simply by adding ammonia borane to an ethanol solution of copper sulfate. Different types of alkynes including aryl–aryl, aryl–alkyl, and aliphatic alkynes were selectively reduced to ( Z )-alkenes affording up to 99% isolated yield. The semihydrogenation of terminal alkynes to alkenes and gram-scale applications were also reported. In addition to eliminating catalyst preparation, the proposed approach is simple and practical and serves as a suitable alternative method to the conventional Lindlar catalyst.