NHC-Ag/Pd-Catalyzed Reductive Carboxylation of Terminal Alkynes with CO₂ and H₂: A Combined Experimental and Computational Study for Fine-Tuned Selectivity

Reductive carboxylation of terminal alkynes utilizing CO₂ and H₂ as reactants is an interesting and challenging transformation. Theoretical calculations indicated it would be kinetically possible to obtain cinnamic acid, the reductive carboxylation product, from phenylacetylene in a CO₂/H₂ system with an N-heterocyclic carbene (NHC)-supported Ag/Pd bimetallic catalysts through competitive carboxylation/hydrogenation cascade reactions in one step. These calculations were verified experimentally with a poly-NHC-supported Ag/Pd catalyst. By tuning the catalyst composition and reaction temperature, phenylacetylene was selectively converted to cinnamic acid, hydrocinnamic acid, or phenylpropiolic acid in excellent yields.