Revealing the Mechanism of Combining Best Properties of Homogeneous and Heterogeneous Catalysis in Hybrid Pd/NHC Systems

• Published in: Angewandte Chemie Vol. 136; no. 27
• Main Authors: Prima, Darya O., Kulikovskaya, Natalia S., Novikov, Roman A., Kostyukovich, Alexander Yu, Burykina, Julia V., Chernyshev, Victor M., Ananikov, Valentine P.
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 01.07.2024
• Subjects: Catalysis; hybrid catalysts; Hybrid structures; Hybrid systems; ligand effect; ligand-nanoparticle interactions; Ligands; Metal surfaces; Nanoparticles; NMR; Nuclear magnetic resonance; Palladium; solid-state NMR; Transition metals
• ISSN: 0044-8249; 1521-3757
• DOI: 10.1002/ange.202317468

The formation of transient hybrid nanoscale metal species from homogeneous molecular precatalysts has been demonstrated by in situ NMR studies of catalytic reactions involving transition metals with N‐heterocyclic carbene ligands (M/NHC). These hybrid structures provide benefits of both molecular complexes and nanoparticles, enhancing the activity, selectivity, flexibility, and regulation of active species. However, they are challenging to identify experimentally due to the unsuitability of standard methods used for homogeneous or heterogeneous catalysis. Utilizing a sophisticated solid‐state NMR technique, we provide evidence for the formation of NHC‐ligated catalytically active Pd nanoparticles (PdNPs) from Pd/NHC complexes during catalysis. The coordination of NHCs via C(NHC)−Pd bonding to the metal surface was first confirmed by observing the Knight shift in the 13C NMR spectrum of the frozen reaction mixture. Computational modeling revealed that as little as few NHC ligands are sufficient for complete ligation of the surface of the formed PdNPs. Catalytic experiments combined with in situ NMR studies confirmed the significant effect of surface covalently bound NHC ligands on the catalytic properties of the PdNPs formed by decomposition of the Pd/NHC complexes. This observation shows the crucial influence of NHC ligands on the activity and stability of nanoparticulate catalytic systems. This research explores the formation of hybrid nanoscale metal species from molecular precatalysts, which exhibit the unique attributes of molecular complexes and nanoparticles. This study addresses their detection difficulties and introduces solid‐state NMR to demonstrate the generation of catalytically active Pd nanoparticles from Pd/NHC complexes. The findings underscore the critical role of NHC ligands in catalytic nanoparticle system stability and activity.