deacetalization-Knoevenagel Condensation Research Articles

Bifunctional two-dimensional copper-organic framework for high catalytic performance on cycloaddition of CO2 with epoxides and deacetalization-Knoevenagel condensation

Due to the larger external surface areas and more accessible active sites, two-dimensional (2D) metal-organic frameworks (MOFs) have aroused great interest in the catalytic field. Herein, the exquisite combination of Cu2+ and designed flexible tetracarboxylic acid of 1,1′-(1,3-phenylenebis(methylene))bis(1H-benzo[d]imidazole-5,6-dicarboxylic acid) (H4PBDA) under the solvothermal condition offers a highly robust 2D network of [Cu(H2PBDA)(H2O)]n (NUC-130), which are interlaced via hydrogen-bonding interactions to form a 3D skeleton. After removing associated solvent molecules by activation, NUC-130a is a scarcely reported Lewis acid/Brönsted acid mediated host framework, which can serve as a promising multifunctional catalyst due to the plentiful active sites including exposed penta-coordinated Cu2+ ions, Brønsted acidic sites of -COOH, and Lewis basic sites of Nbenzimidazole atoms and C=O groups. Performed experiments confirmed that NUC-130a had the high catalytic performance on the cycloaddition of CO2 with a series of epoxide derivatives under solvent-free mild conditions. Furthermore, for deacetalization-Knoevenagel condensation based on acid-base catalysis, NUC-130a also shows excellent catalytic activity, which should be ascribed to that dimethyl acetal can be more effectively hydrolyzed by free -COOH group into formyl group than simple Lewis acidic metal sites. Hence, this work not only provides a type of promising catalyst for efficient chemical fixation of CO2 and deacetalization-Knoevenagel condensation, but also opens up an avenue to creating multifunctional MOFs with integrating multiple active sites and larger external surface areas.

Amine-grafted H-MFI zeolite precursors as acidic-basic catalysts for deacetalization-Knoevenagel condensation

Amorphous and semi-crystalline precursors of zeolites have a large number of silanols that can be used to anchor organic functionalities, like silane-based amines, resulting in formation of basic sites. This work describes the use of amorphous and semi-crystalline precursors of H-MFI zeolite reacting with aminopropyltrimethoxysilane (APTMS) to produce bifunctional acidic-basic catalysts for the deacetalization-Knoevenagel condensation. The effect of precursors crystallinity on the catalytic performance is explained by the formation of Brønsted acidic sites, which catalyze the deacetalization step, and on the propylamine anchoring capacity, controlled by the amount of external silanols present in the aluminosilicate. It is shown that the aluminosilicates with lower crystallinity provide a higher yield of the end product ethyl trans-α-cyanocinnamate due to the greater number of grafted propylamine groups. These results provide new insights into the preparation of acidic-basic catalysts for converting bulky molecules.

Insight into the In-Situ Encapsulation-Reassembly Strategy To Fabricate PW12@NiCo-LDH Acid-Base Bifunctional Catalysts.

Acid-base bifunctional catalysts have attracted increasing attention due to the improved overall efficiency of synthetic reactions. Herein, we reported the successful fabrication of a PW12@NiCo-LDH acid-base bifunctional catalyst by using the in-situ encapsulation-reassembly strategy. The evolution process of morphology and structure was monitored carefully by various time-dependent characterizations. X-ray absorption fine structure (XAFS) and density functional theory (DFT) calculations demonstrated that the terminal oxygen of PW12 in PW12@NiCo-LDH preferred to assemble with the oxygen vacancies on NiCo-LDH. When applied for deacetalization-Knoevenagel condensation, the PW12@NiCo-LDH displayed >99% conversion of benzaldehyde dimethyl acetal (BDMA) and >99% yield of ethyl α-cyanocinnamate (ECC). Moreover, PW12@NiCo-LDH can be recycled at least 10 cycles without obvious structural change, which can be attributed to the confinement of PW12 into the NiCo-LDH nanocage. Such excellent catalytic activity of PW12@NiCo-LDH was benefited from the short mass transfer pathway between acid sites and base sites, which was caused by the stable assembly between PW12 and NiCo-LDH.

Carboxamide functionality grafted entangled Co(II) framework as a unique hydrogen-bond-donor catalyst in solvent-free tandem deacetalization-Knoevenagel condensation with pore-fitting-mediated size-selectivity.

Concerning environmentally benign catalysis with reduced chemical usage, less energy consumption, and waste minimization, metal-organic frameworks (MOFs) with spatially isolated task-specific functionalities not only execute atom-economic important reactions but also enable size-exclusive catalysis at the interface of structure-function synergy. Herein, we synthesized a bipillar-layer Co(II) MOF from the dicarboxylate ligand and carboxamide moiety grafted pyridyl linker. The framework contains a [Co2(COO)4N4] secondary building unit (SBU) and shows excellent hydrolytic stability due to ample non-covalent interactions among the highly conjugated aromatic struts. Notably, the carboxamide functionalities remain free and are perfectly positioned throughout the one-dimensional channels of the framework, wherein three-fold interpenetration of the structure largely increases their density along the pore wall. Benefiting from these structural features, the activated MOF acts as an unprecedented organocatalyst in tandem deacetalization-Knoevenagel condensation towards electronically assorted substrates that were additionally characterized using single-crystal X-ray diffraction. Importantly, the reaction occurs under solvent-free mild conditions, and high catalyst reusability is recorded. In this one-pot cascade reaction, substrates with molecular dimensions larger than that of the three-fold interpenetration generated optimized pore-aperture undergo insignificant conversion, and therefore a rare molecular-dimension-induced size-selectivity is demonstrated. The catalytic route is detailed based on a battery of control experiments, including juxtaposing the performance of an isostructural MOF without any linker functionalization. Compared to the common Lewis acid mediated route, the results explicitly corroborate the first-ever substrate activation via hydrogen bonding to prepare coumarin derivatives via a tandem pathway, and shed light on this futuristic unconventional catalysis using contemporary materials and avoiding major operative glitches.

Lewis acid-base integrated robust metal-organic framework and reconfigurable composite for solvent-free Biginelli condensation and tandem catalysis with size selectivity

Aiming at environmentally benign catalyses with less energy consumption, reduction in chemical usage and minimization of wastes, metal-organic frameworks (MOFs) combining basic functionality enriched pores and unsaturated metal centers (UMCs) is most promising. Alternatively, astute tuning of channel dimension in these materials can benefit much anticipated size-exclusive catalysis, whereas fabrication of flexible MOF-composite is imperative considering facile applicability over real-life platforms. The pillar-bilayered and hydrolytically robust MOF, built from tri-carboxylate ligand, linear linker and solvent-bound [Cd3(COO)6] secondary building unit exhibits N-functionality enriched porous channels and activation-driven generation of open metal sites. Benefiting from unique bifunctional character, the MOF acts as excellent solvent-free catalyst toward one-pot Biginelli reaction and deacetalization–Knoevenagel condensation under mild condition. Both the reactions transpire with broad substrate scope, high recyclability and superior activity to contemporary materials, wherein single-crystal X-ray diffraction is first time applied as product characterization tool. Judiciously designed control experiments validate individual catalytic routes, thereby substantiating the importance of contrasting pore-functionalities at the interface of structure–property synergism. To the best of three-component coupling and acid-base tandem catalysis, substrates with incompatible molecular dimension to that of the twofold interpenetration generated optimized pores exhibit insignificant conversion and demonstrate unprecedented pore-fitting-actuated size selectivity. In view of practically advanced and eco-friendly substrate design, reconfigurable MOF–cotton fiber composite is fabricated via in situ growth, which delivered excellent yields for both these reactions with comparable reusability to that of pristine framework, delineating a paradigm shift to smart, futuristic and green strategy in synergistic catalysis.

Fluorine-Functionalized NbO-Type {Cu2}-Organic Framework: Enhanced Catalytic Performance on the Cycloaddition Reaction of CO2 with Epoxides and Deacetalization-Knoevenagel Condensation.

The high catalytic activity of metal-organic frameworks (MOFs) can be realized by increasing their effective active sites, which prompts us to perform the functionalization on selected linkers by introducing a strong Lewis basic group of fluorine. Herein, the exquisite combination of paddle-wheel [Cu2(CO2)4(H2O)] clusters and meticulously designed fluorine-funtionalized tetratopic 2',3'-difluoro-[p-terphenyl]-3,3″,5,5″-tetracarboxylic acid (F-H4ptta) engenders one peculiar nanocaged {Cu2}-organic framework of {[Cu2(F-ptta)(H2O)2]·5DMF·2H2O}n (NUC-54), which features two types of nanocaged voids (9.8 Å × 17.2 Å and 10.1 Å × 12.4 Å) shaped by 12 paddle-wheel [Cu2(COO)4H2O)2] secondary building units, leaving a calculated solvent-accessible void volume of 60.6%. Because of the introduction of plentifully Lewis base sites of fluorine groups, activated NUC-54a exhibits excellent catalytic performance on the cycloaddition reaction of CO2 with various epoxides under mild conditions. Moreover, to expand the catalytic scope, the deacetalization-Knoevenagel condensation reactions of benzaldehyde dimethyl acetal and malononitrile were performed using the heterogenous catalyst of NUC-54a. Also, NUC-54a features high recyclability and catalytic stability with excellent catalytic performance in subsequent catalytic tests. Therefore, this work not only puts forward a new solution for developing high-efficiency heterogeneous catalysts, but also enriches the functionalization strategies for nanoporous MOFs.

Chemorobust 4p-5p {InPb}-organic framework for efficiently catalyzing cycloaddition of CO2 with epoxides and deacetalization-Knoevenagel condensation

Due to that the high charge density and small radius render In3+ cation a stronger Lewis acidity, multifunctional nanoporous In-MOFs have become one of the most promising catalysts for their high activity. Herein, the solvothermal self-assembly by employing 2,4,6-tri (2,4-dicarboxyphenyl)pyridine (H6TDP) as organic linker leads to a robust honeycomb skeleton of {[(CH3)2NH2][InIIIPbII(TDP) (H2O)]⋅3DMF⋅3H2O}n (NUC-52) with the merits of nanoscopic channels, high porosity (61.3%), large specific surface area, and thermal stability. To the best of our knowledge, this is the first 4p-5p heterometallic {InIIIPbII} cluster-based nano-porous host framework, whose activated state possesses the coexistence of Lewis acid-base sites including 7-coordinated Pb2+ ions, 4-coordinated In3+ ions, uncoordinated carboxyl oxygen atoms, and Npyridine atoms. Performed catalytic experiments exhibited that activated NUC-52 owned the high catalytic activity on the cycloaddition reactions of styrene oxide with CO2 under mild conditions with excellent turnover number (2475) and turnover frequency (619 h−1). Moreover, activated NUC-52 could greatly accelerate the deacetalization-Knoevenagel condensation reactions of benzaldehyde dimethyl acetal and malononitrile. Hence, this work lays down the groundwork for constructing heterometallic cluster-based nanoporous MOFs with excellent Lewis acidic catalysis and chemical stability, which should be ascribed to the reasonable coordination arrangement between organic ligands and distinct metal ions according to the hard–soft acid–base (HSAB) theory.

Nanoporous {Y2}-Organic Frameworks for Excellent Catalytic Performance on the Cycloaddition Reaction of Epoxides with CO2 and Deacetalization-Knoevenagel Condensation.

Stable metal-organic frameworks containing periodically arranged nanosized pores and active Lewis acid-base active sites are considered as ideal candidates for efficient heterogeneous catalysis. Herein, the exquisite combination of [Y2(CO2)7(H2O)2] cluster (abbreviated as {Y2}) and multifunctional linker of 2,4,6-tri(2,4-dicarboxyphenyl)pyridine (H6TDP) led to a nanoporous framework of {[Y2(TDP)(H2O)2]·5H2O·4DMF}n (NUC-53, NUC = North University of China), which is a rarely reported binuclear three-dimensional (3D) framework with hierarchical tetragonal-microporous (0.78 nm) and octagonal-nanoporous (1.75 nm) channels. The inner walls of these channels are aligned by {Y2} clusters and plentifully coexisted Lewis acid-base sites of YIII ions and Npyridine atoms. Furthermore, NUC-53 has a quite large void volume of ∼65.2%, which is significantly higher than most documented 3D rare-earth-based MOFs. The performed catalytic experiments exhibited that activated NUC-53 showed a high catalytic activity on the cycloaddition reactions of CO2 with styrene oxide under mild conditions with excellent turnover number (TON: 1980) and turnover frequency (TOF: 495 h-1). Moreover, the deacetalization-Knoevenagel condensation reactions of benzaldehyde dimethyl acetal and malononitrile could be efficiently prompted by the heterogeneous catalyst of NUC-53. These findings not only pave the way for the construction of nanoporous MOF based on rare-earth clusters with a variety of catalytic activities but also provide some new insights into the catalytic mechanism.

A nanocaged cadmium-organic framework with high catalytic activity on the chemical fixation of CO2 and deacetalization-knoevenagel condensation

Heterogeneous MOFs catalysts have attracted great attention due to the efficient combination of heterogeneity (easy post-reaction separation and recyclability) and homogeneity (active sites and porosity), which inspire us to explore functional MOFs materials with higher catalytic activity on the chemical fixation of CO2 and deacetalization-Knoevenagel condensation. Herein, the self-assembly of Cd2+ and H6TDP under acidic solvothermal condition generated one cadmium-organic framework of {[(CH3)2NH2]2 [Cd2 (TDP) (H2O)2]⋅3DMF⋅2H2O}n (NUC-29, H6TDP = 2,4,6-tris(2,4-dicarboxyphenyl)pyridine) with nano-caged voids and hierarchical microporous channels, which were built on the combination of two kinds of mononuclear units of [Cd (1) (COO)3(H2O)] and [Cd (2) (COO)3(H2O)]. After the removal of solvent molecules by activation, NUC-29 possesses the coexistence of Lewis acid-base sites on the inner surface of channels including all exposed Cd2+ sites and Npyridine sites, which render it an excellent recyclable heterogeneous catalyst to facilitate the cycloaddition reaction of epoxides with CO2 and deacetalization-Knoevenagel condensation under mild conditions.

Polyaromatic Carboxylate Ligands Based Zn(II) Coordination Polymers for Ultrasound-Assisted One-Pot Tandem Deacetalization–Knoevenagel Reactions

Solvothermal reactions between the polyaromatic group containing carboxylic acid pro-ligands 5-{(pyren-1-ylmethyl)amino}isophthalic acid (H2L1) and 5-{(anthracen-9-ylmethyl)amino}isophthalic acid (H2L2) with Zn(NO3)2·6H2O led to the formation of the new 1D coordination polymer [Zn(L1)(NMF)]n (1) and four other coordination polymers, [Zn(L1)(DMF)]n (2), [Zn(L1)(4,4′-Bipy)]n (3), [Zn(L2)(DMF)(H2O)2]n·n(H2O) (4) and [Zn2(L2)2(DMF)(CH3OH)]n (5), which were previously reported by our group. Single crystal X-ray diffraction analyses revealed that the CP 1 has a one-dimensional (1D) double-chain-type structure similar to that of CP 2. For CP 3, the assembly of the Zn(II) ion with a deprotonated L12− ligand and 4,4′-bipyridine produces a 3D network. CP 4 and 5 exhibit 1D linear and 2D layered-type structures. The ultrasound-assisted tandem reactions promoted by CPs have not yet been well studied. Thus, in the present work, we have investigated the catalytic activities of the newly synthesized CP 1, as well as of the other CPs 2–5, towards the tandem deacetalization–Knoevenagel condensation reactions of various acetals under ultrasonic irradiation. They proved to be highly efficient, with special emphasis on catalyst 1, which completely converted the substrate (benzaldehyde dimethyl acetal) into the desired product (2-benzylidenemalononitrile) after 2 h. The stability of the catalysts, namely regarding the action of ultrasonic radiation, was demonstrated by their reuse, where only a slight loss of activity was observed after four cycles. Heterogeneity was also demonstrated, and no leaching was detected over the various cycles.

Nanochannel-based {BaZn}-organic framework for catalytic activity on the cycloaddition reaction of epoxides with CO2 and deacetalization-Knoevenagel condensation.

Herein, the rare combination of BaII (5s) and ZnII (3d) in the presence of the structure-oriented TDP6- ligand generated the nanochannel-based hybrid material {[(CH3)2NH2]2[BaZn(TDP)(H2O)]·DMF·5H2O}n (NUC-51, H6TDP = 2,4,6-tri(2,4-dicarboxyphenyl)pyridine), which possesses excellent physicochemical characteristics such as nanoscopic channels, high porosity, large specific surface area, and high heat/water-resistance. To the best of our knowledge, this is the first 3D [BaIIZnII(CO2)6(H2O)]-based nano-porous host framework, whose activated state possesses the coexistence of Lewis acid-base sites including 4-coordinated Zn2+ ions, 7-coordinated Ba2+ ions, uncoordinated carboxyl oxygen atoms, and Npyridine atoms. Catalytic experiments exhibited that activated NUC-51a possesses a high catalytic activity on the cycloaddition reactions of epoxides with CO2 at 55 °C, which can be ascribed to its structural advantages of nanoscale channels and rich bifunctional active sites. Moreover, NUC-51a could significantly accelerate the deacetalization-Knoevenagel condensation reaction in DMSO solvent at 70 °C.

Construction of acid-base bifunctional covalent organic frameworks via Doebner reaction for catalysing cascade reaction.

We report herein a series of quinoline-4-carboxylic acid linked COFs via the multicomponent one-pot in situ Doebner reaction. The obtained acid-base bifunctional COFs are chemically stable and can highly promote one-pot cascade deacetalization-Knoevenagel condensation reaction in a heterogeneous way under solvent-free conditions.

Porous liquids unlock a new class of spatially orthogonal catalyst

Catalytic cascades epitomize green chemistry principles, enabling ultra-efficient transformations while minimizing unit operations. In the last Chem issue, Chen et al. demonstrate a new strategy to combine antagonistic catalytic functions by incorporating an acidic zeolite in the pores of a sterically hindered, basic ionic liquid to drive a deacetalization-Knoevenagel condensation cascade. Catalytic cascades epitomize green chemistry principles, enabling ultra-efficient transformations while minimizing unit operations. In the last Chem issue, Chen et al. demonstrate a new strategy to combine antagonistic catalytic functions by incorporating an acidic zeolite in the pores of a sterically hindered, basic ionic liquid to drive a deacetalization-Knoevenagel condensation cascade. A bifunctional zeolitic porous liquid with incompatible Lewis pairs for antagonistic cascade catalysisChen et al.ChemSeptember 22, 2021In BriefUnique bifunctional type III porous-liquid (PL)-based systems were facilely fabricated via assembly of zeolite nanosheets with ionic liquids. Rational structural design afforded PLs featured by high zeolite concentration, stable dispersion after 2 years, abundant cavity distribution, and involvement of antagonistic groups (acid and base sites) in separated and active form via steric hindrance control and electronic repulsion regulation. These unique properties worked cooperatively to fulfill the cascade deacetalization-Knoevenagel/Aldol condensation in one pot with catalytic efficiency outperforming the traditional systems. Full-Text PDF

Nanochannel {InZn}-Organic Framework with a High Catalytic Performance on CO2 Chemical Fixation and Deacetalization-Knoevenagel Condensation.

The rare combination of InIII 5p and ZnII 3d in the presence of a structure-oriented TDP6- ligand led to a robust hybrid material of {(Me2NH2)[InZn(TDP)(OH2)]·4DMF·4H2O}n (NUC-42) with the interlaced hierarchical nanochannels (hexagonal and cylindrical) shaped by six rows of undocumented [InZn(CO2)6(OH2)] clusters, which represented the first 5p-3d nanochannel-based heterometallic metal-organic framework. With respect to the multifarious symbiotic Lewis acid-base and Brønsted acid sites in the high porous framework, the catalytic performance of activated NUC-42a upon CO2 cycloaddition with styrene oxide was evaluated under solvent-free conditions with 1 atm of CO2 pressure, which exhibited that the reaction could be well completed at ambient temperature within 48 h or at 60 °C within 4 h with high yield and selectivity. Moreover, because of the acidic function of metal sites and a central free pyridine in the TDP6- ligand, deacetalization-Knoevenagel condensation of acetals and malononitrile could be efficiently facilitated by an activated sample of NUC-42a under lukewarm conditions.

Chemically Robust and Bifunctional Co(II)-Framework for Trace Detection of Assorted Organo-toxins and Highly Cooperative Deacetalization-Knoevenagel Condensation with Pore-Fitting-Induced Size-Selectivity.

Acute detection of assorted classes of organo-toxins in a practical environment is an important sustainable agenda, whereas cooperative and recyclable catalysis can mitigate hazards by minimizing energy requirements and reducing waste generation. We constructed an acid-/base-stable Co(II)-framework with a unique network topology, wherein unidirectional porous channels are decorated by anionic [Co2(μ2-OH)(COO)4(H2O)3] secondary building units and neutral [CoN2(COO)2] nodes. An intense luminescent signature of the hydrolytically robust framework is harnessed for the selective, fast-responsive, and regenerable detection of two detrimental organo-aromatics, 4-aminophenol (4-AP) and 2,4,6-trinitrophenol (TNP). Alongside remarkable quenching, their nanomolar detection limits (4-AP: 99.5 nM; TNP: 67.2 nM) rank among the lowest reported values in water and corroborate their ultra-sensitivity. Density functional theory (DFT) calculations verify the electron-transfer route of sensing through portraying redistribution of energy levels of molecular orbitals in a three-dimensional network by each analyte and further envisages non-covalent host-guest interactions. Benefiting from the concurrent existence of an open-metal site and a triphenylamine-moiety-functionalized ligand, the activated framework acts as an outstandingly cooperative heterogeneous catalyst in deacetalization-Knoevenagel condensation under mild conditions. The acid-base dual catalysis is detailed for the first time from combined inputs of control experiments and DFT validations. To the best of tandem reaction, larger-sized substrate exhibits insignificant conversion, and certifies rarest pore-fitting induced size-selectivity.

1D Zn(II) Coordination Polymers as Effective Heterogeneous Catalysts in Microwave-Assisted Single-Pot Deacetalization-Knoevenagel Tandem Reactions in Solvent-Free Conditions

The new 1D CPs [Zn(L1)(H2O)4]n.nH2O (1) and [Zn(L2)(H2O)2]n (2) [L1 = 1,1′-(ethane-1,2-diyl)bis(6-oxo-1,6-dihydropyridine-3-carboxylic acid); L2 = 1,1′-(propane-1,3-diyl)bis(6-oxo-1,6-dihydropyridine-3-carboxylic acid)] were prepared from flexible dicarboxylate pro-ligands (H2L1 and H2L2). Both CPs 1 and 2 were characterized by elemental, FTIR, and powder X-ray diffraction analysis. Their geometry and the structural features were unveiled by single-crystal X-ray diffraction analysis. The underlying topology of the CPs was illustrated by the topological analysis of the H-bonded structure of CP 1, which revealed a 3,4,6-connected trinodal net. On the other hand, topological analysis on the hydrogen-bonded network of CP 2 showed a 2,3,3,4,6,7-connected hexanodal net. The thermal stability of the CPs was investigated by thermogravimetric analysis. CPs 1 and 2 act as heterogeneous catalysts in one-pot tandem deacetalization–Knoevenagel condensation reactions under environmentally mild conditions. CPs 1 exhibits a yield of ca. 91% in a microwave-assisted solvent-free medium, whereas a slightly lower yield was obtained for CP 2 (87%) under the same experimental protocol. The recyclability of catalyst 1 was also assessed. To our knowledge, these are the first Zn(II)-based CPs to be applied as heterogeneous catalysts for the above tandem reactions under environmentally friendly conditions.

Rational Design of Pomegranate-like Base-Acid Bifunctional β Zeolite by Steam-Assisted Crystallization for the Tandem Deacetalization-Knoevenagel Condensation.

A highly crystalline pomegranate-like base-acid bifunctional beta zeolite was successfully synthesized by the steam-assisted crystallization method using a basic nitrided N-beta as the starting material. The secondary crystal growth of a beta zeolite generating acid functionality occurred over the outer surface and intercrystalline void spaces of the N-beta zeolite. The pomegranate-like N-beta@H-beta zeolite had a high surface area and base-acid dual functionality because of the well-connected framework topologies of the H-beta and N-beta crystallites. The N-beta@H-beta zeolite exhibited a superior yield of benzylidenemalononitrile during the tandem deacetalization-Knoevenagel condensation of benzaldehyde dimethyl acetal and malononitrile compared to H-beta, N-beta, and their physical mixture. This is likely due to the isolated and balanced activity of the base- and acid-catalyzed reactions.

A spatially orthogonal hierarchically porous acid–base catalyst for cascade and antagonistic reactions

Complex organic molecules are of great importance to research and industrial chemistry and typically synthesized from smaller building blocks by multistep reactions. The ability to perform multiple (distinct) transformations in a single reactor would greatly reduce the number of manipulations required for chemical manufacturing, and hence the development of multifunctional catalysts for such one-pot reactions is highly desirable. Here we report the synthesis of a hierarchically porous framework, in which the macropores are selectively functionalized with a sulfated zirconia solid acid coating, while the mesopores are selectively functionalized with MgO solid base nanoparticles. Active site compartmentalization and substrate channelling protects base-catalysed triacylglyceride transesterification from poisoning by free fatty acid impurities (even at 50 mol%), and promotes the efficient two-step cascade deacetalization-Knoevenagel condensation of dimethyl acetals to cyanoates.

Continuous Flow Pickering Emulsion Catalysis in Droplet Microfluidics Studied with In Situ Raman Microscopy.

Pickering emulsions (PEs), emulsions stabilized by solid particles, have shown to be a versatile tool for biphasic catalysis. Here, we report a droplet microfluidic approach for flow PE (FPE) catalysis, further expanding the possibilities for PE catalysis beyond standard batch PE reactions. This microreactor allowed for the inline analysis of the catalytic process with in situ Raman spectroscopy, as demonstrated for the acid‐catalyzed deacetalization of benzaldehyde dimethyl acetal to form benzaldehyde. Furthermore, the use of the FPE system showed a nine fold improvement in yield compared to the simple biphasic flow system (FBS), highlighting the advantage of emulsification. Finally, FPE allowed an antagonistic set of reactions, the deacetalization–Knoevenagel condensation, which proved less efficient in FBS due to rapid acid‐base quenching. The droplet microfluidic system thus offers a versatile new extension of PE catalysis.

Ion-Exchange Fabrication of Hierarchical Al-MOF-Based Resin Catalysts for the Tandem Reaction.

Metal-organic framework (MOF)-supported macroscale resin catalysts, IRA900(xOH)-MIL-101(Al)-NH2 (x means the concentration of NaOH), with spatially isolated antagonistic acid-base active sites were successfully synthesized through a novel strategy by ion exchange and in situ solvothermal methods. The hierarchical pore system of the as-prepared catalysts effectively promotes the mass transfer and contacts with catalytic active centers during the organic reactions. Therefore, the environmentally friendly catalysts exhibit excellent superior activity and stability in one-pot deacetalization-Knoevenagel condensation reaction, and the yield by optimal IRA900(0.2OH)-MIL-101(Al)-NH2 reaches close to 99% after 5 h at 110 °C. Thanks to the millimeter-sized resin carrier and robust sphere morphology, the recycling of the as-prepared catalysts only requires natural sedimentation. This work presents an effective strategy to build low-toxic acid-base catalysts by combining the advantages of ion-exchange resins and functionalized MOF materials.