Pd@Zn-MOF-74: Restricting a Guest Molecule by the Open-Metal Site in a Metal-Organic Framework for Selective Semihydrogenation.

In this work, we found that the open-metal site in a metal-organic framework (MOF) can be used to enhance such selectivity. Hydrogenation of phenylacetylene over such a catalyst enables ultrahigh styrene selectivity of 92% at full conversion with a turnover frequency of 98.1 h-1. The origin of ultrahigh selectivity, as unveiled by density functional theory calculation, is due to a coordination interaction between the open Zn(II) site and the C≡C bond of phenylacetylene.

Significant Enhancement of C2 H2 /C2 H4 Separation by a Photochromic Diarylethene Unit: A Temperature- and Light-Responsive Separation Switch.

A dual temperature- and light-responsive C2 H2 /C2 H4 separation switch in a diarylethene metal-organic framework (MOF) is presented. At 195 K and 100 kPa this MOF shows ultrahigh C2 H2 /C2 H4 selectivity of 47.1, which is almost 21.4 times larger than the corresponding value of 2.2 at 293 K and 100 kPa, or 15.7 times larger than the value of 3.0 for the material under UV at 195 K and 100 kPa. The origin of this unique control in C2 H2 /C2 H4 selectivity, as unveiled by density functional calculations, is due to a guest discriminatory gate-opening effect from the diarylethene unit.

Photoswitching adsorption selectivity in a diarylethene-azobenzene MOF.

The first MOF (metal-organic framework) built on both diarylethene and azobenzene photochromic units is reported here and displays distinct photoresponses for different guest molecules, thus creating an easy-to-use pathway to modulate the adsorption selectivity of MOF materials.

Optimization of reaction conditions towards multiple types of framework isomers and periodic-increased porosity: luminescence properties and selective CO2 adsorption over N2.

Three new metal-organic frameworks (MOFs) were prepared by solvo(hydro)thermolysis and further characterized as framework isomers. The structural transformation from non-porous to porous MOFs and the purity of these products can be modulated by controlling the reaction temperature. The periodic-increased porosity observed was further confirmed by CO2 adsorption isotherms. Owing to the presence of acylamide groups in the pore walls and the flexible nature of the skeleton of these MOFs, highly selective CO2 adsorption over N2 was observed, as well as structure-dependent periodic varieties in luminescence properties.

Promising long-lasting phosphor material: a novel metal-organic framework showing intriguing luminescent performance.

A distinct way to target long-lasting phosphors (LLPs) is disclosed. This new material is a metal-organic framework featuring a 1D zig-zag chain and 3D hydrogen bonded PtS net with three-fold interpenetration. It exhibits persistent luminescence lasting about 1 s which can be traced by the naked eye. The green persistent luminescence is exclusively due to emission from multiple triplet excited states. In this way, LLP can be easily achieved by using a simple hydrothermal synthesis without any codopant that in nature is responsible for well-known inorganic LLPs.

Insights into the dual activation mechanism involving bifunctional cinchona alkaloid thiourea organocatalysts: an NMR and DFT study.

In-depth understanding of the activation mechanism in asymmetric organocatalysis is of great importance for rational development of highly efficient catalytic systems. In this Article, the mechanism for the direct vinylogous Michael reaction of α,ß-unsaturated γ-butyrolactam (Nu) and chalcone (EI) catalyzed by the bifunctional cinchona alkaloid thiourea organocatalyst (Cat) was studied with a combination of experimental (NMR) and theoretical (DFT) approaches, through which a new dual activation pathway was found. The key feature of this new dual activation mechanism (Pathway C) is that one N-H(A) of the thiourea moiety and the N-H of the protonated amine in Cat simultaneously activate Nu, while the other N-H(B) of the thiourea moiety activates EI. Both the NMR measurement and the DFT calculation identified that the interaction of Cat with Nu is stronger than that with EI in the catalyst-substrate complexes. Kinetic studies via variable-temperature NMR measurements indicated that, with the experimental activation energy E(a) of 10.2 kcal/mol, the reaction is all first-order in Nu, EI, and Cat. The DFT calculation further revealed that the C-C bond formation is both the rate-determining and the stereoselectivity-controlling steps. In agreement with the experimental data, the energy barrier for the rate-determining step along Pathway C was calculated as 8.8 kcal/mol. The validity of Pathway C was further evidenced by the calculated enantioselectivity (100% ee) and diastereoselectivity (60:1 dr), which are in excellent match with the experimental data (98% ee and >30:1 dr, respectively). Mechanistic study on the Michael addition of nitromethane to chalcone catalyzed by the Catalyst I further identified the generality of this new dual activation mechanism in cinchona alkaloid thiourea organocatalysis.