Rhodium(I) catalyst supported on polymer crystal surfaces: Further hydrogenation studies

Gordon, Bernard; Butler, Jacqueline S.; Harrison, I. R.

doi:10.1002/pola.1987.080250810

Cited by 6 publications

(1 citation statement)

References 4 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…We also observed that the polymer-supported Wilkinson's catalyst beads appear to be very sensitive to conditions allowing efficient diffusion of the reactants and products into and out of the beads. Long activation times, sometimes greater than 1 h at elevated temperatures, were needed before the catalyst became active, presumably allowing the beads to swell and expose their catalytic centers . Furthermore, having high flow rates of gas that produced good stirring of the beads and long bubbling times (more than 1 min) to ensure saturation of the solution with H 2 were critical to consistently observe polarization with this catalyst.…”

Section: Resultsmentioning

confidence: 99%

para-Hydrogen-Induced Polarization in Heterogeneous Hydrogenation Reactions

et al. 2007

View full text Add to dashboard Cite

We demonstrate the creation and observation of para-hydrogen-induced polarization in heterogeneous hydrogenation reactions. Wilkinson's catalyst, RhCl(PPh3)3, supported on either modified silica gel or a polymer, is shown to hydrogenate styrene into ethylbenzene and to produce enhanced spin polarizations, observed through NMR, when the reaction was performed with H2 gas enriched in the para spin isomer. Furthermore, gaseous phase para-hydrogenation of propylene to propane with two catalysts, the Wilkinson's catalyst supported on modified silica gel and Rh(cod)(sulfos) (cod = cycloocta-1,5-diene; sulfos = -O3S(C6H4)CH2C(CH2PPh2)3) supported on silica gel, demonstrates heterogeneous catalytic conversion resulting in large spin polarizations. These experiments serve as a direct verification of the mechanism of heterogeneous hydrogenation reactions involving immobilized metal complexes and can be potentially developed into a practical tool for producing catalyst-free fluids with highly polarized nuclear spins for a broad range of hyperpolarized NMR and MRI applications.

show abstract

Section: Resultsmentioning

confidence: 99%

para-Hydrogen-Induced Polarization in Heterogeneous Hydrogenation Reactions

et al. 2007

View full text Add to dashboard Cite

show abstract

Parahydrogen-Induced Polarization in Heterogeneous Catalytic Processes

Kovtunov

Живонитко

Skovpin

et al. 2012

Topics in Current Chemistry

119

167

View full text Add to dashboard Cite

Parahydrogen-induced polarization of nuclear spins provides enhancements of NMR signals for various nuclei of up to four to five orders of magnitude in magnetic fields of modern NMR spectrometers and even higher enhancements in low and ultra-low magnetic fields. It is based on the use of parahydrogen in catalytic hydrogenation reactions which, upon pairwise addition of the two H atoms of parahydrogen, can strongly enhance the NMR signals of reaction intermediates and products in solution. A recent advance in this field is the demonstration that PHIP can be observed not only in homogeneous hydrogenations but also in heterogeneous catalytic reactions. The use of heterogeneous catalysts for generating PHIP provides a number of significant advantages over the homogeneous processes, including the possibility to produce hyperpolarized gases, better control over the hydrogenation process, and the ease of separation of hyperpolarized fluids from the catalyst. The latter advantage is of paramount importance in light of the recent tendency toward utilization of hyperpolarized substances in in vivo spectroscopic and imaging applications of NMR. In addition, PHIP demonstrates the potential to become a useful tool for studying mechanisms of heterogeneous catalytic processes and for in situ studies of operating catalytic reactors. Here, the known examples of PHIP observations in heterogeneous reactions over immobilized transition metal complexes, supported metals, and some other types of heterogeneous catalysts are discussed and the applications of the technique for hypersensitive NMR imaging studies are presented.

show abstract