The Union Carbide catalyst (Cp2Cr + SiO2), studied by solid-state NMR

Schnellbach, Michael; Köhler, Frank H.; Blümel, Janet

doi:10.1016/0022-328x(96)06295-x

Cited by 41 publications

(64 citation statements)

References 29 publications

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“…Since the 31 P chemical shifts change somewhat with temperature, this line broadening might be due to an increased temperature gradient along the rotor with faster sample spinning. 13 However, taking into account that the half-widths of the 31 P signals of our model compounds are in the range of several hundred hertz (maximum for 8, 350 Hz), these changes are not very spectacular.…”

Section: Dependence Of Magnetization Transfer On Contact Timementioning

confidence: 98%

“…31 P, 13 C, 29 Si), which also reduces the recycle delays, can be used. Indeed, CP works well with spinning speeds of up to 4 kHz, as for example our previous work shows.…”

Section: Introductionmentioning

confidence: 99%

“…Even most special pulse sequences, 43 -48 among them the popular ones applying a ramp in the S (dilute nuclei) or I (abundant nuclei) channels, 35,49 -55 often require rotor synchronization or at least special skill in adjusting the pulse durations and power levels. Furthermore, most of the presented techniques used 13 C NMR of isotopically enriched samples, and rather 'easy' compounds.…”

Section: Introductionmentioning

confidence: 99%

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³¹P CP/MAS NMR of polycrystalline and immobilized phosphines and catalysts with fast sample spinning

Reinhard

Blümel

2003

Magnetic Reson in Chemistry

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Cross-polarization (CP) at fast magic angle spinning (MAS) frequencies leads to a splitting of the Hartmann-Hahn (HH) matching profile into a centerband and additional bands of higher orders. The matching profiles differ with the substance categories. Therefore, signal intensity is usually lost, when e.g. the routine standard NH 4 H 2 PO 4 is used for optimizing the 1 H-31 P HH match prior to measuring phosphines and their metal complexes in polycrystalline or immobilized form. Here, a variety of model compounds, such as Ph 2 PCH 2 CH 2 PPh 2 and (CO) 2 Ni(PPh 3 / 2 , which can be used as 31 P CP standards for analogous substances or materials are presented. Investigating the influences of MAS frequency, contact time, 1 H pulse power and sample volume on the matching profiles of the model compounds leads to general trends. Thereby, a new strategy for measuring difficult samples with CP at high MAS rates has been developed: their optimum CP parameters are derived from the most intense maxima in the HH matching profiles of the corresponding model compounds. This new strategy is compared with variations of a conventional ramp sequence. Although the latter generally provide smaller signal half-widths, the new strategy leads to higher signal intensities. The new method was successfully applied to polycrystalline and immobilized phosphines and catalysts.

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Section: Dependence Of Magnetization Transfer On Contact Timementioning

confidence: 98%

“…31 P, 13 C, 29 Si), which also reduces the recycle delays, can be used. Indeed, CP works well with spinning speeds of up to 4 kHz, as for example our previous work shows.…”

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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³¹P CP/MAS NMR of polycrystalline and immobilized phosphines and catalysts with fast sample spinning

Reinhard

Blümel

2003

Magnetic Reson in Chemistry

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“…[5] The interesti na dsorbed metal complexes, and specifically metallocenes,a rises from their importance as precursors for catalysts. [7,8] Oprunenko and Günther investigated biphenylene chromium tricarbonylc omplexes in the polycrystalline state and adsorbed on silica. [6] Early research in our group resulted in as tudy of paramagnetic chromocenes in adsorbed and polycrystalline form.…”

Section: Introductionmentioning

confidence: 99%

“…[6] Early research in our group resulted in as tudy of paramagnetic chromocenes in adsorbed and polycrystalline form. [10,11] In all the cases described in the literature, [3][4][5][7][8][9][10][11] successful adsorption of as pecies is apparent through unique solid-state NMR featuresd ue to the high mobilities of the adsorbate moleculeso nt he surface. [9] Later,w es tudied various diamagnetic and paramagnetic metallocenes and demonstrated that they can be adsorbed on amorphous high-surface-area silica gel.…”

Section: Introductionmentioning

confidence: 99%

Adsorption of Metallocenes on Silica

Cluff

Blümel

2016

Chemistry A European J

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The adsorption of the metallocenes ferrocene, doubly deuterated ferrocene, cymantrene and nickelocene, as well as molybdenum hexacarbonyl, proceeds in the absence of a solvent. Large single pieces of silica gel were placed in contact with the solid metallocenes and the adsorption process was visualized on a macroscopic scale and the maximal loadings were determined. H, H, and C solid-state NMR studies confirmed fast isotropic reorientation of the surface-adsorbed metallocene molecules within the pores of the silica. All prevalent anisotropic solid-state interactions were averaged out. The solid diamagnetic and paramagnetic materials were amenable to measurements with a standard solution NMR instrument. All metallocenes adsorbed in a monolayer. In the case of ferrocene and cymantrene, different C MAS signals were obtained for the cyclopentadienyl ring carbon nuclei and assigned to one ring interacting with the surface and one ring pointing away from it. The relative adsorption strengths of ferrocene on different silica supports, nanotubes, and activated carbon were determined by a novel straightforward method recording the desorption temperature. The reversibility of adsorption has been demonstrated by competition experiments using ferrocene, doubly deuterated ferrocene, and cymantrene. Adsorbed nickelocene could be reduced to small Ni aggregates on the surface and the catalytic activity of the resulting material for the cyclotrimerization of phenylacetylene was proven.

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Homogeneous Chromium Catalysts for Olefin Polymerization

Theopold

1998

Eur. J. Inorg. Chem.

265

179

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The Union Carbide catalyst (Cp2Cr + SiO2), studied by solid-state NMR

Cited by 41 publications

References 29 publications

³¹P CP/MAS NMR of polycrystalline and immobilized phosphines and catalysts with fast sample spinning

³¹P CP/MAS NMR of polycrystalline and immobilized phosphines and catalysts with fast sample spinning

Adsorption of Metallocenes on Silica

Homogeneous Chromium Catalysts for Olefin Polymerization

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The Union Carbide catalyst (Cp2Cr + SiO2), studied by solid-state NMR

Cited by 41 publications

References 29 publications

31P CP/MAS NMR of polycrystalline and immobilized phosphines and catalysts with fast sample spinning

31P CP/MAS NMR of polycrystalline and immobilized phosphines and catalysts with fast sample spinning

Adsorption of Metallocenes on Silica

Homogeneous Chromium Catalysts for Olefin Polymerization

Contact Info

Product

Resources

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³¹P CP/MAS NMR of polycrystalline and immobilized phosphines and catalysts with fast sample spinning

³¹P CP/MAS NMR of polycrystalline and immobilized phosphines and catalysts with fast sample spinning