The Role of Ligands and Silver(I) Additives in the Ligand-Promoted Divergent α,β-Dehydrogenation of Aliphatic Acids
Zhewei Li, Yanhui Tang, Ming Lei
Abstract
Herein, the density functional theory method was employed to investigate the mechanism of the ligand-promoted divergent α,β-dehydrogenation of aliphatic acids. The calculated results showed that the ligands could act as an intramolecular base to activate both β-methylene C(sp 3 )-H and α-methylene C(sp 3 )-H bonds via concerted metalation–deprotonation mechanism to generate α,β-unsaturated aliphatic acids and the β-C(sp 3 )-H activation is the rate-determining step. The origin of the selective activation of different kinds of C–H bonds and different product inhibition effects by two ligands was explained by the different torsional strains between the substrate and the Pd catalysts. The formation of lactone includes the C–C coupling process and the cyclization process. The C–C coupling is catalyzed by the heterodimeric Pd(II)–Ag(I) species and reveals the pivotal role of the base. The final cyclization process is catalyzed by the silver additives. In addition, the formation of Z -products undergoes a unique rotational isomerization promoted by Ag(I)–Ag(I) species to complete the E -to- Z isomerization. In general, this theoretical work indicates that in this cascade reaction, the active catalytic species go through the process from monomeric Pd species in the C–H activation process and heterodimeric Pd–Ag species in the C–C coupling process to homodimeric Ag–Ag species in the final cyclization process.