Studies on catalytic activity of MIL-53(Al) and structure analogue DUT-5(Al) using bdc- and bpdc-ligands functionalized with l-proline in a solid-solution mixed-linker approach

N-Heterocyclic Carbene Silver Complex Modified Polyacrylonitrile Fiber/MIL-101(Cr) Composite as Efficient Chiral Catalyst for Three-Component Coupling Reaction

Complex asymmetric synthesis can be realized by the chiral induction of amino acids in nature. It is of great significance to design a new biomimetic catalytic system for asymmetric synthesis. In this context, we report the preparation and characterization of the composite of polyacrylonitrile fiber (PANF) and metal-organic framework to catalyze the chiral synthesis of propargylamines. A confined microenvironment is established with N-heterocyclic carbene (NHC) silver complex-supported PANF and D-proline-encapsulated MIL-101(Cr). This novel supported catalyst demonstrated high activity in addition to excellent stereoselectivity in the three-component reaction between alkynes, aldehydes, and amines (A3). The regeneration can be realized by adsorption of D-proline again when the stereoselectivity decreases after recycle uses. By regulating the confined microenvironment on the composite, the activity and selectivity of the catalytic system are improved with turnover numbers of up to 2800 and 98% ee. The biomimetic catalytic system to A3 coupling reaction is systematically studied, and the synergistic catalytic mechanism between NHC-Ag and D-proline in the confined microenvironment is revealed.

Dissecting the effects of water guest adsorption and framework breathing on the AlO4(OH)2 centres of metal-organic framework MIL-53 (Al) by solid state NMR and structural analysis

The relationship between the adsorption of water on MIL-53 (Al) MOF, the structural phase of MIL-53 (Al), and the quadrupole coupling constant of ²⁷Al framework aluminium atom (QCC) of the MOF AlO₄(OH)₂ centres (Al-sites) has been investigated by combining solid-state ²⁷Al MAS NMR spectroscopy with XRD analysis and DFT calculations. It is established that ²⁷Al QCC is primarily sensitive to water adsorption to the Al-sites and by a minor extent to the framework contraction/expansion interconversions. We thus conclude that the ²⁷Al MAS NMR method is sensitive enough to differentiate the effects of pore contractions and water adsorption to Al-sites basing on the changes of the QCC value.

Defect-Engineered Chiral Metal-Organic Frameworks for Efficient Asymmetric Aldol Reaction

By employment of a mixed truncated chiral ligand synthetic strategy, a defect-engineered chiral metal-organic framework with hierarchical micro/mesoporous structure was prepared, and it exhibited efficient heterogeneous catalytic activity and enantioselectivity for asymmetric aldol reaction.

Molecular Mobility of Tert-butyl Alcohol Confined in a Breathing MIL-53 (Al) Metal-Organic Framework

We present a detailed solid-state NMR characterization of the molecular dynamics of tert-butyl alcohol (TBA) confined inside breathing metal-organic framework (MOF) MIL-53(Al). ²⁷ Al MAS NMR has demonstrated that TBA adsorption induces the iX phase of MIL-53 material with partially shrunk channels. ² H solid-state NMR has shown that the adsorbed alcohol exhibits anisotropic rotations of the methyl groups around two C 3 axes and librations of the molecule as a whole about the axis passing through the TBA C-O bond. These librations are realized by two distinct ways: fast molecule orientation change during the translational jump diffusion along the channel with characteristic time τ_D of about 10^-9  s at 300 K; slow local librations at a single coordination site, representing framework hydroxyl groups, with τ_l ≈10^-6  s at 300 K. Self-diffusion coefficient of the alcohol in the MOF has been estimated: D=3.4×10^-10  m²  s^-1 at 300 K. It has been inferred that both the framework flexibility and the interaction with framework hydroxyl groups define the dynamics of TBA confined in the channels of MIL-53 (Al).

Probing the limits of linker substitution in aluminum MOFs through water vapor sorption studies: mixed-MOFs instead of mixed-linker CAU-23 and MIL-160 materials

Only water vapor sorption isotherms were able to reveal the mixed-MOF instead of mixed-linker material formation of CAU-23 and MIL-160.

Dynamics of isobutane is a sensitive probe for framework breathing in MIL-53 (Al) MOF

²H solid-state NMR shows that the dynamics of adsorbed isobutane is very sensitive to MIL-53 framework breathing detected by ²⁷Al MAS NMR.