Mechanistic Insights into Pd-Catalyzed Hydrofunctionalization of 1,3-Dienes: A Theoretical Study

The generation of the π-allylpalladium complex is the key step in the Pd-catalyzed hydrofunctionalization of 1,3-dienes, but the mechanism remains ambiguous. Commonly accepted mechanisms, such as Pd-H migratory insertion and ligand-to-ligand hydrogen transfer (LLHT), meet unfavorable thermodynamics and the requirements of coordination capacity, which may not be general for all situations. Herein, we conducted a calculation study to compare the possibility of three different pathways among several cases of Pd-catalyzed hydrofunctionalization. The results demonstrated that the π-Lewis base activation mode may be a rational pathway for the generation of the π-allylpalladium complex, in which molecular orbital (MO) and natural population analysis (NPA) indicate the nucleophilicity of 1,3-diene is activated through η²-coordination by a Pd(0) catalyst. The enantioselectivity study showed that the π-Lewis base activation mode evades ligand dissociation and maintains a rigid stereoselective environment, which provides a guarantee for the enantioselectivity of the reaction. This work suggested that the π-Lewis base activation mode was worth considering when exploring the mechanism for the Pd-catalyzed hydrofunctionalization of 1,3-diene.