rhodium-catalyzed transfer hydrogenation of cinnamic acid using formic acid as the hydrogen source

Hydrogenation is a chemical reaction in which molecular hydrogen (h2) is added to an unsaturated compound, converting it to a saturated one. it is a key reaction in organic chemistry, playing a pivotal role in the synthesis of fine chemicals, pharmaceuticals, and materials. among the various methods, transfer hydrogenation has gained attention as a practical and eco-friendly alternative to direct hydrogenation, eliminating the need for pressurized hydrogen gas. in this study, an efficient transfer hydrogenation of cinnamic acid catalyzed by cyclooctadiene rhodium chloride dimer was developed. formic acid proved to be the most effective hydrogen source within this catalytic system, particularly in the presence of triethylamine. the catalyst demonstrated high selectivity, efficiently reducing the alkene functional group while leaving the carboxyl group unchanged. the research also focused on the optimization of various reaction parameters, including catalyst percentage, temperature, solvent, hydrogen donor, and base. high yields were achieved, with 10% and 5% rhodium catalyst at 65 °c and 85 °c, respectively. even with just 2% rhodium catalyst, a 47% yield was obtained, showing significant improvements over previous studies.