Investigating the Mechanism of Palladium-Catalyzed Radical Oxidative C(sp3 )-H Carbonylation: A DFT Study.

Palladium (Pd)-catalyzed radical oxidative C-H carbonylation of alkanes is a useful method for functionalizing hydrocarbons, but there is still a lack of understanding of the mechanism, which restricts the application of this reaction. In this work, density functional theory (DFT) calculations were carried out to study the mechanism for a Pd-catalyzed radical esterification reaction. Two plausible reaction pathways have been proposed and validated by DFT calculations. The computational results reveal that the generated alkyl radical prefers to add to the carbon monoxide (CO) molecule to form a carbonyl radical before bonding with the Pd species. Radical addition onto Pd followed by CO migratory insertion was unfavorable owing to the high energy barrier of the migratory insertion step. The regioselectivity of the C(sp3 )-H carbonylation was also investigated by DFT. The results show that the regioselectivity is controlled by both the bond dissociation energy of the reacting C-H bond and the stability of the corresponding generated carbon radical. Competitive side reactions also affected the yield and regioselectivity owing to the rapid consumption of the stable radical intermediate.