A modular approach for the synthesis of highly ordered porous and chiral auxiliary (Evans auxiliary) decorated metal-organic frameworks is developed. Our synthesis strategy, which uses known porous ...structures as model materials for incorporation of chirality via linker modification, can provide access to a wide range of porous materials suitable for enantioselective separation and catalysis. Chiral analogues of UMCM-1 have been synthesized and investigated for the enantioseparation of chiral compounds in the liquid phase and first promising results are reported.
A coprecipitation method has been applied successfully for the preparation of 0.5
wt.% palladium supported on MOF-5. The apparent surface area was roughly 900
m
2/g, the specific micropore volume was ...0.3
cm
3/g, and the powder X-ray diffractograms showed good coincidence with the theoretical pattern of MOF-5. In the hydrogenation of ethyl cinnamate with molecular hydrogen the specific activity of palladium supported on MOF-5 was twice as high as that of a commercial Pd/C catalyst with the same Pd content. It was shown that “true” heterogeneous catalysis takes place, i.e. leached palladium does not contribute to the reaction. In repeated runs the palladium supported on MOF-5 did not show any loss in activity, but a complete loss of micro pore volume was observed. Thus, it can be assumed that the palladium is not located inside the micropores but probably bonds to the outer surface of the crystals.
1H and 27Al MAS NMR spectroscopies have been applied for studying the effect of water molecules, nitrogen bases, and o-xylene on the hydroxyl protons of bridging AlOH groups and framework aluminum ...atoms in the metal−organic framework (MOF) MIL-53. For water molecules adsorbed on the low-temperature form MIL-53lt, two 1H MAS NMR signals were found indicating the formation of different O−H···O hydrogen bonds to neighboring oxygen atoms, such as to carboxylic oxygens. Upon adsorption of the nitrogen bases acetonitrile, ammonia, and pyridine, a linear increase of the quadrupole coupling constant, C Q, of the framework aluminum atoms in dehydrated MIL-53 from C Q = 8.5 MHz (unloaded material) to maximum 10.8 MHz (pyridine-loaded material) as a function of the proton affinity of the adsorbates was observed. Adsorption of o-xylene led to three stepwise changes of the quadrupole coupling constants, C Q, of framework aluminum atoms in dehydrated MIL-53. While the first two stepwise changes of the C Q values (C Q = 8.0 and 8.7 MHz) occur for o-xylene loadings of lower than 4 molecules per unit cell and for all AlO4(OH)2 centers, the third change of the C Q value to 9.4 MHz was observed for o-xylene loadings higher than 4 o-xylene molecules per unit cell and for maximum 50% of the framework aluminum atoms. This third adsorbate-induced change of the C Q value of framework aluminum atoms in MIL-53 is accompanied by a significant decrease of the adsorbate mobility.
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► Pd in MOF Pd(2-pymo)
2
n
was reduced to Pd
0 during hydrogenation reactions. ► Shape-selective hydrogenation of 1-octene took place in the first 4
h of reaction time. ► After ...leaching out the formed Pd
0 nanoparticles, cyclododecene was hydrogenated. ► Formation of Pd
0 was followed by in-situ XRD experiments in a hydrogen atmosphere. ► Protonation of the linker during hydrogenation was shown by solid-state NMR.
The MOF Pd(2-pymo)
2
n
(2-pymo
=
2-pyrimidinolate) was used in the liquid-phase hydrogenation of 1-octene and cyclododecene. Up to a reaction time of 4
h, reactant shape selectivity could be observed, i.e. 1-octene was hydrogenated, but not the more bulky molecule cyclododecene. However, if the catalyst was exposed to hydrogen for more than 4
h, also the hydrogenation of cyclododecene took place. Visually a color change of the catalyst was observed and by XRD it was found that Pd
0 nanoparticles were formed and that the MOF Pd(2-pymo)
2
n
was transformed into a new crystalline phase, where the Pd
0 seemed to be accessible. Additionally, Pd
0 was leached out and was available for hydrogenation. When reusing the MOF after reaction times less than 1
h, the reaction rate increased with every reuse. We assume that even in the first 4
h Pd
0 was formed, but could not be detected by XRD. In-situ XRD measurements exposing the MOF to hydrogen in the gas phase showed that the MOF was much more stable in gas phase hydrogenation, because the MOF structure remained intact even when Pd
0 was formed.
A modular approach for the synthesis of highly ordered porous and chiral auxiliary (Evans auxiliary) decorated metal–organic frameworks is developed. Our synthesis strategy, which uses known porous ...structures as model materials for incorporation of chirality via linker modification, can provide access to a wide range of porous materials suitable for enantioselective separation and catalysis. Chiral analogues of UMCM-1 have been synthesized and investigated for the enantioseparation of chiral compounds in the liquid phase and first promising results are reported.
Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.
A modular approach for the synthesis of highly ordered porous and chiral auxiliary (Evans auxiliary) decorated metal–organic frameworks is developed. Our synthesis strategy, which uses known porous ...structures as model materials for incorporation of chirality via linker modification, can provide access to a wide range of porous materials suitable for enantioselective separation and catalysis. Chiral analogues of UMCM-1 have been synthesized and investigated for the enantioseparation of chiral compounds in the liquid phase and first promising results are reported.
Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.
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