Parahydrogen-Induced Polarization in Heterogeneous Hydrogenations Catalyzed by an Immobilized Au(III) Complex

Hydrogenation of unsaturated compounds with parahydrogen can lead to an enhancement of the NMR signals of reaction products by several orders of magnitude. Parahydrogen-induced polarization (PHIP) of nuclear spins is useful for developing both novel MRI applications as well as hypersensitive tools for operando studies in catalysis, but until recently, PHIP was observed only in homogeneous hydrogenations. To assess the potential of combining PHIP with heterogeneous catalysis, heterogeneous gas-phase hydrogenation of propene and propyne with parahydrogen was carried out using a Au(III) Schiff base complex immobilized within a metal−organic framework material IRMOF-3. Observation of PHIP in the 1H NMR spectra of reaction products implies that both hydrogen atoms of a single H2 molecule are transferred as a pair to the same product molecule and supports the conclusions made earlier that the well-defined isolated Au(III) centers of this catalyst are the active sites involved in hydrogen activation.