Late-stage hydrogen isotope exchange and dearomatization reactions under D2 have recently been used for preparing labeled compounds using metal nanoparticle catalysts. In the case of dearomatization, lower rates are usually observed under D2 compared to H2 as a result of a kinetic isotope effect. Here, we report the synthesis of NHC-stabilized PdNPs, their characterization, and their use for the reduction of 2-phenylpyridine to 2-phenylpiperidine or 2-phenylpiperidine-d6, which reveals an unexpected preference for D2 over H2. This effect is observed using NPs stabilized by polyvinylpyrrolidone (Pd@PVP) but is more pronounced in the presence of NHC ligands (Pd@NHC). DFT calculations reveal that the phenomenon arises from a higher surface concentration of deuterides relative to hydrides in both systems, which is enhanced by the electronic influence of NHC ligands. This study provides the first report and mechanistic insight into an unusual isotopic effect in NP-catalyzed deuteration, highlighting the pivotal role of ligand-NP interactions.
Suárez-Riaño et al. (Fri,) studied this question.