Metal-organic frameworks (MOFs) are ac lass of crystalline porousm aterials that have been activelyu sed for several industrial and synthetica pplications.M OFs are spatially and geometrically extrapolatedc oordination polymers with intriguing properties such as tunable porosity and dimensionality.Int erms of their catalytic efficiency,MOFs combine the easy recoverability of heterogeneous catalysts with the increased selectivity of biological catalysts. It is therefore not surprising that alot of work on optimizing MOF catalysts for organic transformationsh as been carriedo ut over the past decade. In this review,recent developments in MOF catalysis are summarized, with special attention being paid to CÀC, CÀN, and CÀOc oupling reactions. The influence of pore size, pore environment, and load on catalytic activity is described. Post-synthetics tabilization techniques and hostguest interactions in caged MOF scaffolds are detailed. Mechanistic aspects pertaining to the use of MOFs in asymmetric heterogeneousc atalysis are highlighted and categorized.

The efficacy of heterogeneous catalysis relies heavily on diffusion and distribution of reactants within catalyst supports. However, the presence of confinement, essential for reaction selectivity, drastically slows down molecular transport. Here, macro-mesoporous silica inverse opal (SiO 2 À IO) films were used as a model system to study the rather unexplored molecular infiltration behavior using a probe molecule resembling a catalyst via confocal laser scanning microscopy (CLSM). CLSM analysis revealed homogeneous tracer distribution in SiO 2 À IO and attachment to both transport and mesopores. Bulk macro-mesoporous SiO 2 À IO support was used for the attachment of mono-and bis-functionalized chiral Rh-diene complexes, and the catalytic activity and selectivity with respect to the support was studied. Lower enantioselectivity was observed with the bis-functionalized ligand due to ligand entanglement and reduced accessibility of the active site, while the monofunctionalized ligand gave an excellent enantioselectivity of 94 %ee in the asymmetric 1,2-addition of triphenylboroxine to N-tosylimines and could be recycled up to three times.

Studying the interaction between organic molecules and metal oxide surfaces is key to the development and modification of organic–inorganic hybrids for application in heterogeneous catalysis, biomedical implants, and functional nanoporous matrices.

Mesoporous catalyst supports that mimic the spatially confined active sites of enzymes can aid in the development of highly selective molecular heterogeneous catalysts. Nontemplated mesoporous SiO 2 (NT-mSiO 2 ) materials with open porosity, tunable pore sizes, and high diffusivity are promising candidates in this regard. However, the operationalization of such materials strongly depends on the controlled passivation of their external pore surfaces. This enables catalyst molecules to be selectively immobilized on the internal pore surface where the desired spatial confinement effects can be observed. In this work, confocal laser scanning microscopy (CLSM) is presented as a viable analytical tool to visualize the passivation efficiency and permeability of NT-mSiO 2 platelets consisting of interconnected mesopores (d pore = 9.4 nm) with positive pore wall curvatures. CLSM investigations with representative fluorescent probe molecules show that after pore-filling with Pluronic P123, the passivating film is constrained to the external platelet surface. The permeability of different passivating films based on mono and bifunctional silanes is compared. A pyrene-based organosilane is used as a tracer molecule to determine the covalent functionalization susceptibility of passivated NT-mSiO 2 platelets. Additionally, SiO 2 nanospheres with modular particle sizes are synthesized using an L-lysine-mediated sol−gel process and assembled into NT-mSiO 2 with tunable pore sizes. Hexamethyldisilazane-passivated NT-mSiO 2 (d pore = 4.3 nm) is used as a catalyst support for the immobilization of cationic molybdenum imido alkylidene N-heterocyclic carbene complexes to study the effect of confinement on monomacrocyclization selectivity in ring-closing olefin metathesis reactions. A 31% enhancement in monomacrocyclization selectivity is observed when compared to the homogeneous catalyst.

Oxide inverse opals (IOs) with their high surface area and open porosity are promising candidates for catalyst support applications. Supports with confined mesoporous domains are of added value to heterogeneous catalysis. However, the fabrication of IOs with mesoporous or sub-macroporous voids (<100 nm) continues to be a challenge, and the diffusion of tracers in quasi-mesoporous IOs is yet to be adequately studied. In order to address these two problems, we synthesized ZnO IOs films with tunable pore sizes using chemical bath deposition and template-based approach. By decreasing the size of polystyrene (PS) template particles towards the mesoporous range, ZnO IOs with 50 nm-sized pores and open porosity were synthesized. The effect of the template-removal method on the pore geometry (spherical vs. gyroidal) was studied. The infiltration depth in the template was determined, and the factors influencing infiltration were assessed. The crystallinity and photonic stop-band of the IOs were studied using X-Ray diffraction and UV-Vis, respectively. The infiltration of tracer molecules (Alexa Fluor 488) in multilayered quasi-mesoporous ZnO IOs was confirmed via confocal laser scanning microscopy, while fluorescence correlation spectroscopy analysis revealed two distinct diffusion times in IOs assigned to diffusion through the pores (fast) and adsorption on the pore walls (slow).

Non‐porous polyurethane‐based monoliths are prepared under solvent‐induced phase separation conditions. They possess low specific surface areas of 0.15 m2 g−1, pore volumes of 1 µL g−1, and a non‐permanent, solvent‐induced microporosity with pore dimensions ≤1 nm. Mesoporosity can be introduced by varying the monomers and solvents. A tuning of the average solubility parameter of the solvent mixture by increasing the macroporogen content results in a decrease in the volume fraction of micropores from 70% to 40% and an increase in the volume fraction of pores in the range of 1.7–9.6 nm from 22% to 41% with only minor changes in the volume fraction of larger mesopores in the range of 9.6–50 nm. The polymeric monoliths are functionalized with quaternary ammonium groups, which allowed for the immobilization of an ionic liquid that contained the ionic Rh‐catalyst [1‐(pyrid‐2‐yl)‐3‐mesityl)‐imidazol‐2‐ylidene))(η4‐1,5‐cyclooctadiene)Rh(I) tetrafluoroborate]. The supported catalyst is used in the hydrosilylation of 1‐alkynes with dimethylphenylsilane under continuous flow using methyl‐tert‐butyl ether as second liquid transport phase. E/Z‐selectivity in hydrosilylation is compared to the one of the analogous biphasic reactions. The strong increase in Z‐selectivity is attributed to a confinement effect provided by the small mesopores.

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The application of ZnO materials as solid‐state supports for molecular heterogeneous catalysis is contingent on the functionalization of the ZnO surface with stable self‐assembled monolayers (SAMs) of catalyst linker molecules. Herein, experimental and theoretical methods are used to study SAMs of azide‐terminated molecular catalyst linkers with two different anchor groups (silane and thiol) on poly and monocrystalline (0001, ) ZnO surfaces. Angle‐resolved and temperature‐dependent X‐ray photoelectron spectroscopy (XPS) is used to study SAM binding modes, thermal stabilities, and coverages. The binding strengths and atomistic ordering of the SAMs are determined via atom‐probe tomography (APT). Density functional theory (DFT) and ab initio molecular dynamics (AIMD) calculations provide insights on the influence of the ZnO surface polarity on the interaction affinity and conformational behavior of the SAMs. The investigations show that SAMs based on 3‐azidopropyltriethoxysilane possess a higher binding strength and thermal stability than the corresponding thiol. SAM surface coverage is strongly influenced by the surface polarity of ZnO, and the highest coverage is observed on the polycrystalline surface. To demonstrate the applicability of linker‐modified polycrystalline ZnO as a catalyst support, a chiral Rh diene complex is immobilized on the azide‐terminal of the SAM and its coverage is evaluated via XPS.