A theoretical study on chemo- and regioselective Rh-catalyzed hydroformylation and hydrogenation of propyne

A comprehensive theoretical investigation on the mechanism of hydroformylation and hydrogenation of propyne catalyzed by the modified catalyst HRh(CO)2(PH3) is carried out employing a nonlocal density functional method (B3LYP). There are a number of possible pathways for this catalytic cycle. It comes to the conclusion from computation that the propyne insertion into Rh-H bond step is irreversible and thus the regioselectivity-limiting step for the whole catalytic cycle. The results from calculation indicate that the energy barrier for hydroformylation of propyne is obviously lower than that of hydrogenation, so hydroformylation of propyne could be easier than propyne hydrogenation. The main product is trans-butenal originated from hydroformylation and can be further hydrogenated to give birth to butanal at last.