When Bifunctional Catalyst Encounters Dual MLC Modes: DFT Study on the Mechanistic Preference in Ru-PNNH Pincer Complex Catalyzed Dehydrogenative Coupling Reaction

Abstract

Metal ligand cooperation (MLC) plays an important role in the development of homogeneous catalysts. Two major MLC modes have generally been proposed, known as the M-L bond mode and the (de)aromatization mode. To reveal the role of the dual potential functional sites on the MLC process, we present a detailed mechanistic study on a novel-designed Ru-PNNH complex possessing dual potential MLC functional sites for the M-L bond mode and the (de)aromatization mode, respectively. Our results indicate that the Ru-PNNH complex prefers the M-L mode exclusively during different stages of the catalytic cycle. The unusual double deprotonation process and the mechanistic preference are rationalized. The N-arm deprotonation is attributed to the small steric hindrance of the amido N-arm and the conjugation stabilization effect of the amido group. The origin of the unexpected exclusive mechanistic preference on the M-L bond mechanism is due to the conjugation effect of the amido group, which stabilizes the dearomatized co...