Unveiling Leaching-Oxidizing-Landing Paths of Pd Single-Atom Catalyzed Suzuki-Miyaura Reaction by Ambient Mass Spectrometry

Abstract

The palladium-catalyzed Suzuki-Miyaura cross-coupling (SMCC) reaction is an essential technique for C-C bond formation. It is considered to occur through two distinct pathways involving homogeneous and heterogeneous mechanisms. However, there is still debate about these mechanisms given the lack of direct structural evidence in both spatial and temporal terms, especially regarding the conversion of active Pd species. In this study, the Pd single-atom catalyst (Pd SAC) SMCC reaction was monitored in real-time using ambient mass spectrometry (AMS) to study conversions of Pd species both on the catalyst surface and in the liquid phase. This revealed a leaching-oxidizing-landing paths as a contributor to the heterogeneous process which involves heterogeneous oxidative addition, Pd leaching along with transmetallation (rather than oxidative addition), and subsequent oxidation-landing back onto the catalyst surface. The leaching-oxidizing-landing mechanism of Pd active sites during Pd SAC-catalyzed SMCC reaction provides an explanation for the Pd migration on the catalyst surface. A crucial role of molecular oxygen during SMCC reaction was revealed and attributed to the re-deposition of active Pd species by coordinating with the catalyst support. Overall, the leaching-oxidizing-landing mechanism of the SMCC reaction has been revealed and it not only provides insights into mechanism studies and catalyst designs, but it enlarges AMS applications.