Nickel/Photoredox-catalyzed diastereoselective semihydrogenation of alkynes using a carboxylic acid as a cooperative ligand and hydrogen surrogate

The Z-selective semihydrogenation of alkynes plays a key role in the industrial manufacture of fine chemicals. Considerable research attention has focused on the development of reagents, catalysts, and protocols for stereoselective reduction of alkynes to afford pure cis-alkenes. Here, we report the efficient and diastereoselective semihydrogenation of alkynes to Z-alkenes through synergistic nickel/photoredox catalysis with pivalic acid as the cooperative ligand and proton and electron sources. The mild catalytic approach enables highly efficient, Z-selective semihydrogenation of diverse substrates, including dialkyl alkynes, aryl-alkyl alkynes, and diaryl alkynes, with excellent functional group tolerance. A series of mechanistic experiments and DFT calculations suggest that the stereospecific construction of cis-alkenes was enabled by both the in situ generation of nickel hydrogen and the cooperative ligand effects between the nickel catalyst and carboxylic acid.