Understanding the leaching properties of heterogenized catalysts: A combined solid-state and PHIP NMR study

Silica‐Encapsulated Pt‐Sn Intermetallic Nanoparticles: A Robust Catalytic Platform for Parahydrogen‐Induced Polarization of Gases and Liquids

“…To ensure that this hydrogenation occurs heterogeneously on the iNPs and not homogeneously by leached metal ions, as can occur in immobilized complexes, PHIP experiments were attempted using the supernatant obtained by centrifugation and decanting of the aqueous slurry containing the particles. As shown in Figure S12, no conversion and no PHIP NMR signals could be observed.…”

Synthesis and Solid‐State NMR Characterization of a Robust, Pyridyl‐Based Immobilized Wilkinson's Type Catalyst with High Catalytic Performance

“…As typical examples for phosphine‐containing linkers, the Rh−P type immobilized Wilkinson's catalysts [Rh–P–Wilk] have shown significant catalytic activity in hydrogenation reactions and good separability . However, a gradual loss of the catalytic activity was observed, mainly caused by the leaching of catalytic active species from the surface, as shown by (PHIP) NMR experiments . Furthermore, as phosphine linker groups and ligands are easily oxidized in solution, they become unable to re‐coordinate the rhodium metallic center and the catalytic activity decreases –.…”

Wilkinson‐Type Immobilized Catalyst on Diamond Nanoparticles for Alkene Reduction

“…One important concern in organometallic heterogeneous catalysis is the uncontrolled release of metal ions into solution . To ensure that no rhodium leaching occurs, the catalyst remains on the ND and does not dissociate during the hydrogenation process if using ND–Rh nanoparticles, the hydrogenation of chalcone was stopped after 2 h, and the ND–Rh particles were isolated by centrifugation and filtration.…”

“…Indeed, the 31 Ps pectrum of ND-Rhs hows broad overlapping resonances extending from 15 to 72 ppm andasuperimposed narrower line centered at approximately 53 ppm, in addition to the peak at 37.3 ppm previously assignedt o phosphine oxide groups.T he occurrence of severelyb roadened and more or less structureless signals is very common for surface-bound Wilkinson-type trisphosphine complexes [35,[49][50][51] and resultsf rom the presence of ad istribution of disordered surfacee nvironments, [35,42,46,49,51] and the formationo facomplex mixture of surface-bound complexes, if the phosphine ligand is immobilized prior to its coordination to rhodium. Considering that Wilkinson's catalyst [46,49] and relatedt risphosphine Rh-complexes [35,42,50,51] exhibit chemical shifts between 20 and 80 ppm, and that the signals of the metal-boundp hosphorusa toms in the Rh complex 2 (Scheme 1B)d erived from catecholp hosphine 1 appear in the same region (chemical shifts are 53 and 27 ppm for the P, O-chelating and monodentate ligands, respectively), [47] the broad resonance at 25 ppm could be assigned to Rh-bound phosphines, whereas the narrower line at 53 ppm might evidence the presence of P, O-Rh chelates. To confirm this proposed assignment and further interpretthe 31 PMAS NMR spectrum,2Dhomonuclear J-resolved MAS NMR experiments were performed, allowing the measurement of cis-a nd trans-PÀRhÀP 2 J coupling constants in the solid state.…”

“…One important concern in organometallic heterogeneous catalysis is the uncontrolled release of metal ions into solution. [50,51] To ensure that no rhodiuml eachingo ccurs, the catalyst remainso nt he ND and does not dissociate during the hydrogenation process if using ND-Rh nanoparticles, the hydrogenationo fc halcone was stopped after 2h,a nd the ND-Rh particlesw ere isolated by centrifugation and filtration.T he conversion measured at this stage was 58 %. The resulting catalyst-free solution was then put again under hydrogen pressure for 4h and the conversion remainedu nchanged, giving evidencet hat no furtherh ydrogenation took place in the absence of catalyst.…”