Mechanism of the Rhodium-Catalyzed Hydroformylation of 4-(1-phenylvinyl)pyridine: A Detailed Computational Investigation of the Regioselectivity and Chemoselectivity

摘要

The mechanism of 4-(1-phenylvinyl)pyridine hydroformylation with HRh(CO)(PH_3)_3 as active catalyst has been proposed and discussed by B3LYP. Also, the regioselectivity and chemoselectivity are investigated by calculations and excellent agreement with the existing experimental results is displayed. It is found that the characteristic catalytic cycle is similar to that for olefin hydroformylation: (a) 4-(1-phenylvinyl)pyridine coordination and insertion, (b) CO coordination and insertion, and (c) H2 oxidative addition as well as aldehyde elimination. The rate-limiting and regioselectivity-determining step are H_2 oxidative addition which determines the linear aldehyde product energetically. The competitive hydrogenation is along with (a) 4-(1-phenylvinyl)pyridine coordination and insertion, (b) H_2 oxidative addition followed by hydrogenation product elimination Interestingly, CO coordination is found to be an exothermic (H<0) but endergonic (G>0) process, while the corresponding H_2 process is endergonic and endothermic(H>0), H2 is not competitive with CO from the viewpoint of thermodynamics. But hydrogenation is computed to be more favored than hydroformylation actually, so it can be conclude that the chemoselectivity is controlled by kinetics, not thermodynamics.