Search

A directed heterogeneous C−H activation/halogenation reaction catalyzed by readily synthesized Pd@MOF nanocatalysts was developed. The heterogeneous Pd catalysts used were a novel and environmentally benign Fe-based metal-organic framework (MOF) (Pd@MIL-88B-NH2(Fe)) and the previously developed Pd@MIL-101-NH2(Cr). Very high conversions and selectivities were achieved under very mild reaction conditions and in short reaction times. A wide variety of directing groups, halogen sources, and substitution patterns were well tolerated, and valuable polyhalogenated compounds were synthesized in a controlled manner. The synthesis of the Pd-functionalized Fe-based MOF and the recyclability of the two catalysts are also presented. [ABSTRACT FROM AUTHOR]

The chemical stability of metal-organic frameworks (MOFs) is a major factor preventing their use in industrial processes. Herein, it is shown that judicious choice of the base for the Suzuki-Miyaura cross-coupling reaction can avoid decomposition of the MOF catalyst Pd@MIL-101-NH2(Cr). Four bases were compared for the reaction: K2CO3, KF, Cs2CO3 and CsF. The carbonates were the most active and achieved excellent yields in shorter reaction times than the fluorides. However, powder XRD and N2 sorption measurements showed that the MOF catalyst was degraded when carbonates were used but remained crystalline and porous with the fluorides. XANES measurements revealed that the trimeric chromium cluster of Pd@MIL-101-NH2(Cr) is still present in the degraded MOF. In addition, the different countercations of the base significantly affected the catalytic activity of the material. TEM revealed that after several catalytic runs many of the Pd nanoparticles (NPs) had migrated to the external surface of the MOF particles and formed larger aggregates. The Pd NPs were larger after catalysis with caesium bases compared to potassium bases. [ABSTRACT FROM AUTHOR]

Twofamilies of metal–organic frameworks (MOFs), MIL-88and MIL-101 built by trinuclear transition metal (TM) clusters (TM= Cr, Fe, or Sc), have been known for several years, but their synthesesare often reported separately. In fact, these MOFs are polymorphs,or framework isomers: they are assembled from the same metal secondarybuilding units and organic linkers, but the connectivity of thesecomponents differs. Here we report for the first time the synthesisof the vanadium MOF MIL-88B(V) and compare its synthesis parametersto those of MIL-47(V) and the recently reported MIL-101(V). The propertiesof MIL-88B(V) and MIL-101(V) are remarkably different. MIL-88B(V)can “breathe” and is responsive to different solvents,while MIL-101(V) is rigid and contains mesoporous cages. MIL-101(V)exhibits the highest specific surface area among vanadium MOFs discoveredso far. In addition, both MIL-88B(V) and MIL-101(V) transform to MIL-47at higher temperatures. We have also identified the key synthesisparameters that control the formation of MIL-88B(V), MIL-101(V), andMIL-47: temperature, time, and pH. This relates to the rate of reactionbetween the metal and linkers, which has been monitored by ex situX-ray powder diffraction and V K-edge X-ray absorptionspectroscopy during MOF synthesis. It is therefore important to fullystudy the synthesis conditions to improve our understanding of frameworkisomerism in MOFs. [ABSTRACT FROM AUTHOR]

Remarkably simple Ir III catalysts enable the isomerization of primary and sec-allylic alcohols under very mild reaction conditions. X-ray absorption spectroscopy (XAS) and mass spectrometry (MS) studies indicate that the catalysts, with the general formula [Cp*Ir III ], require a halide ligand for catalytic activity, but no additives or additional ligands are needed., (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The chemical stability of metal-organic frameworks (MOFs) is a major factor preventing their use in industrial processes. Herein, it is shown that judicious choice of the base for the Suzuki-Miyaura cross-coupling reaction can avoid decomposition of the MOF catalyst Pd@MIL-101-NH2 (Cr). Four bases were compared for the reaction: K2 CO3 , KF, Cs2 CO3 and CsF. The carbonates were the most active and achieved excellent yields in shorter reaction times than the fluorides. However, powder XRD and N2 sorption measurements showed that the MOF catalyst was degraded when carbonates were used but remained crystalline and porous with the fluorides. XANES measurements revealed that the trimeric chromium cluster of Pd@MIL-101-NH2 (Cr) is still present in the degraded MOF. In addition, the different countercations of the base significantly affected the catalytic activity of the material. TEM revealed that after several catalytic runs many of the Pd nanoparticles (NPs) had migrated to the external surface of the MOF particles and formed larger aggregates. The Pd NPs were larger after catalysis with caesium bases compared to potassium bases., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A ruthenium trichloride complex has been loaded into an aluminium metal-organic framework (MOF), MOF-253, by post-synthetic modification to give MOF-253-Ru. MOF-253 contains open bipyridine sites that are available to bind with the ruthenium complex. MOF-253-Ru was characterised by elemental analysis, N(2) sorption and X-ray powder diffraction. This is the first time that a Ru complex has been coordinated to a MOF through post-synthetic modification and used as a heterogeneous catalyst. MOF-253-Ru catalysed the oxidation of primary and secondary alcohols, including allylic alcohols, with PhI(OAc)(2) as the oxidant under very mild reaction conditions (ambient temperature to 40 °C). High conversions (up to >99%) were achieved in short reaction times (1-3 h) by using low catalyst loadings (0.5 mol% Ru). In addition, high selectivities (>90%) for aldehydes were obtained at room temperature. MOF-253-Ru can be recycled up to six times with only a moderate decrease in substrate conversion., (Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)