Nickel-Catalyzed Transfer Hydrogenation of Unactivated Aryl Alkenes with Hydrosilane as Hydrogen Source

A nickel-catalyzed transfer hydrogenation of aryl alkenes has been developed using hydrosilane as the hydrogen source. Sterically hindered disubstituted or trisubstituted alkenes were employed to test the efficiency of this transformation. Mechanism studies showed that hydrogenation took place smoothly with more sterically-hindered trans-alkenes. While uncongested cis-alkenes could hardly convert to the alkanes but hydrosilylation products were generated instead. Moreover, certain amount of water was found to be a promotion for the protonation process and could partly serve as the hydrogen source. Not only for simple stilbenes, this easy handle protocol also showed tolerance for substrates involving other unsaturated groups as well as heterocycles.