Indium Metal–Organic Frameworks as High-Performance Heterogeneous Catalysts for the Synthesis of Amino Acid Derivatives

Two Zn(II)/Cd(II) Coordination Polymers as Recyclable Heterogeneous Catalysts for an Efficient Room-Temperature Synthesis of α-Aminonitriles via the Solvent-Free Strecker Reaction

The α-aminonitriles are versatile building blocks in the synthesis of natural or artificial amino acids as well as important intermediates in organic synthesis. For their synthesis, the three-component Strecker reaction involving an aldehyde or a ketone together with amines and trimethylsilyl cyanide is used. In the literature, hydrothermally produced metal-based heterogeneous Lewis acid catalysts have been utilized in various solvents. In this work, we aimed at a greener approach toward such catalysis by (a) making two precatalysts with d¹⁰ metal centers, {[Zn(hipamifba)(H₂O)]·2H₂O}_n (1) and {[Cd(hipamifba)(H₂O)₂]·2H₂O}_n (2) (where H₂hipamifba = 4-(((4-((carboxymethyl) carbamoyl)phenyl)amino)methyl)benzoic acid), via an easy and scalable room-temperature method, and (b) showcasing the use of these coordination polymers (CPs) as very efficient, recyclable, and heterogeneous catalysts for the Strecker reaction to form α-aminonitriles in high yields under solvent-free reaction at ambient conditions. This has also allowed us to demonstrate the importance of open metal sites in such catalysis through an efficiency comparison between activated 1 and 2. In addition, activated 2 exhibited a wide substrate scope including a natural product Girgensohnine, providing an example of a natural product synthesis by a CP catalyst via an organic transformation such as the Strecker reaction.

Framework Adaptability and Concerted Structural Response in a Bismuth Metal-Organic Framework Catalyst

Bismuth metal-organic frameworks (MOFs) as heterogeneous catalysts are scarce, and there is little knowledge on the influence of the MOF features on their resulting activity and behavior. Here, we present the synthesis, characterization, and catalytic activity in the one-pot multicomponent Strecker reaction with ketones of three new MOFs prepared with the combination of indium or bismuth and 4,4',4'',4'''-methanetetrayltetrabenzoic acid. One of them, denoted BiPF-7, is very robust and chemically stable, and demonstrates a high activity in the formation of the desired α-aminonitriles. The interaction of the catalytic substrates with the metal centers in this MOF has been crystallographically characterized, showcasing a concerted framework adaptability process that involves structural changes in framework components that are not directly involved in the binding of the guests.

Sc(iii)-Based metal–organic frameworks

In the universe of MOFs, their construction with Sc(iii) is rather limited. This highlight shows the exciting chronological development of Sc(iii)-MOFs which have afforded promising applications due to their exceptional chemical stability.

Indium-Organic Framework with soc Topology as a Versatile Catalyst for Highly Efficient One-Pot Strecker Synthesis of α-aminonitriles

An In(III) based metal-organic framework (MOF), In-pbpta, with soc topology was constructed from the trigonal prismatic [In3(μ3-O)(H2O)3(O2C-)6] secondary building unit (SBU) and a custom-designed tetratopic linker H4pbpta (pbpta = 4,4',4″,4‴-(1,4-phenylenbis(pyridine-4,2,6-triyl))-tetrabenzoic acid)). The obtained MOF shows a Brunauer-Emmett-Teller surface area of 1341 m2/g with a pore volume of 0.64 cm3/g, which is the highest among the scarcely reported In-soc-MOFs. The constructed MOF demonstrates excellent performance as a heterogeneous Lewis acid catalyst for highly efficient conversion in a one-pot multicomponent Strecker reaction for the preparation of α-aminonitriles under solvent-free conditions, which can be easy to separate and recycle without significant loss of activity for up to seven cycles. The computational modeling studies suggest the presence of the three substrates in close vicinity to the In-oxo cluster. The strong interactions of the aldehyde/ketone and the amine with the In-oxo cluster together with the readily available cyanide ion around the In-oxo cluster lead to high catalytic conversion within a short period of time for the MOF catalyst. Our work therefore lays a foundation to develop MOF as a new class of efficient heterogeneous catalyst for one-pot Strecker reaction.

Enhancing the catalytic behaviour of HKUST-1 by graphene oxide for phenol oxidation

The composites of graphite oxide (GrO) and the HKUST-1 framework were synthesized by the typical solvothermal method and applied as heterogeneous catalysts for catalytic wet peroxide oxidation (CWPO) of phenol. XRD, FT-IR, Raman and SEM were conducted to characterize the samples. For catalytic oxidation of 150 mL 100 mg L^-1 phenol, the dose of 30 mg (0.2 g L^-1) catalysts and 0.46 mL H₂O₂ were kept constant. The GrO-3/HKUST-1 (3% content of GrO) showed higher catalytic activity than the HKUST-1 framework and other GrO/HKUST-1 composites with 99% phenol conversion and 86% COD removal efficiency were obtained at 50°C after 30 min and 8 h. The effect of temperature (40-80°C) and pH (4-9) on catalytic oxidation of phenol by GrO-3/HKUST-1 was investigated. The results showed that the degradation of phenol was obtained with optimum efficiency at 60°C with complete phenol conversion and 93% COD reduction. Furthermore, the acid and alkali resistance abilities were enhanced to a certain degree by the integration of GrO compared with the parent framework HKUST-1. Three successive runs were conducted in the natural pH (6.8) of 150 mL 100 mg L^-1 phenol solution which indicated that the synthesized GrO-3/HKUST-1 composite had satisfactory reusability due to the prevention of carbon deposit and negligible Cu²⁺ leaching (8 ppm). The GrO/HKUST-1 composite could be a kind of promising heterogeneous catalysts for catalytic degradation of organic compounds. Similar to other catalysts, the catalytic oxidation of phenol also relies on the formation of hydroxyl radicals.

Triggering Lewis Acidic Nature through the Variation of Coordination Environment of Cd-Centers in 2D-Coordination Polymers

The rational design and successful synthesis of novel functional metal-organic frameworks relies on careful selection of metals and versatile organic ligands. A newly designed pyrazole-based dicarboxylate ligand, 5-(3,5-dimethyl-1H-pyrazol-1-yl) 1,3-benzenedicarboxylic acid (H₂L), was utilized to obtain two new Cd-based coordination polymers I [Cd(L)(H₂O)]·H₂O and II [Cd(L)] under similar reaction conditions via solvothermal strategy. Single-crystal X-ray data confirmed that compound I exhibits a two-dimensional (2D) skeleton comprising pentagonal bipyramidal Cd-ions and an organic ligand moiety. Compound II has also formed a two-dimensional layer arrangement with the connectivity between trigonal bipyramidal Cd-ions and the organic ligand. Topological analysis revealed that compound I has formed unique 4³.6³ net topology while compound II has displayed a 4⁴.6² sql net topology with 2D frameworks. The Lewis acidic nature of both I and II containing a Cd²⁺ metal center has been correlated with the coordination number through dye adsorption-desorption and catalysis studies. The selective adsorption of anionic dye and the extent of adsorption are interrelated with the Cd-ion geometry. For the first time, the role of coordinated water molecule has been analyzed through heterogeneous catalysis reaction (i.e., cyanosilylation) with Cd-based 2D-coordination polymers (CPs). The plausible mechanisms have been proposed to explain the subsequent role of coordination number and environment in CPs.

Structural variety of aluminium and gallium coordination polymers based on bis-pyridylethylene: from molecular complexes to ionic networks

Diverse molecular (0D and 1D) as well as ionic (0D, 1D, 2D, mixed 1D–2D) crystal structures of complexes of aluminium and gallium trihalides with bis(4-pyridylethylene) were obtained by solvent-free melt reactions.

Two scandium coordination polymers: rapid synthesis and catalytic properties

Two new scandium coordination polymers were synthesized by MW and hydrothermal methods, and exhibited good catalytic performance.

Amide-functionalized ionic indium–organic frameworks for efficient separation of organic dyes based on diverse adsorption interactions

Two amide groups functionalized anionic indium–organic frameworks demonstrated efficient separation of organic dyes based on diverse adsorption interactions, and can be potentially applicable in column-chromatographic separation of dyes.

Calix[4]arene-based polyoxometalate organic–inorganic hybrid and coordination polymer as heterogeneous catalysts for azide–alkyne cycloaddition and Knoevenagel condensation reaction

One POM-based Cu(i)-hybrid and one Cd(ii) compound have been achieved by a calix[4]arene ligand. They exhibit efficient catalytic abilities for azide–alkyne cycloaddition and Knoevenagel condensation reactions, respectively.

Strong Lewis Base Ga4B2O9: Ga-O Connectivity Enhanced Basicity and Its Applications in the Strecker Reaction and Catalytic Conversion of n-Propanol

Heterogeneous solid base catalysis is valuable and promising in chemical industry, however it is insufficiently developed compared to solid acid catalysis due to the lack of satisfied solid base catalysts. To gain the strong basicity, the previous strategy was to basify oxides with alkaline metals to create surficial vacancies or defects, which suffers from the instability under catalytic conditions. Monocomponent basic oxides like MgO are literally stable but deficient in electron-withdrawing ability. Here we prove that a special connectivity of atoms could enhance the Lewis basicity of oxygen in monocomponent solids exemplified by Ga₄B₂O₉. The structure-induced basicity is from the μ₃-O linked exclusively to five-coordinated Ga³⁺. Ga₄B₂O₉ behaved as a durable catalyst with a high yield of 81% in the base-catalyzed synthesis of α-aminonitriles by Strecker reaction. In addition, several monocomponent solid bases were evaluated in the Strecker reaction, and Ga₄B₂O₉ has the largest amount of strong base centers (23.1 μmol/g) and the highest catalytic efficiency. Ga₄B₂O₉ is also applicable in high-temperature solid-gas catalysis, for example, Ga₄B₂O₉ catalyzed efficiently the dehydrogenation of n-propanol, resulting in a high selectivity to propanal (79%). In contrast, the comparison gallium borate, Ga-PKU-1, which is a Brönsted acid, preferred to catalyze the dehydration process to obtain propylene with a selectivity of 94%.

Indium-based metal–organic frameworks as catalysts: synthesis of 2-nitro-3-arylimidazo[1,2-a]pyridines via oxidative amination under air using MIL-68(In) as an effective heterogeneous catalyst

The metal–organic framework MIL-68(In) has emerged as a productive heterogeneous catalyst for the synthesis of 2-nitro-3-arylimidazo[1,2-a]pyridines via oxidative amination between 2-aminopyridines and nitroalkenes using air as an oxidation agent.

Sc2(pydc)2 unit based 1D, 2D and 3D metal–organic frameworks as heterogeneous Lewis acid catalysts for cyanosilylation

Three new Sc-MOFs have been synthesized using H₂pydc linker and Sc(iii) ions. 1 features a ladder-shaped chain, 2 displays a waved layer and 3 exhibits a (3,3)-connected nbo-a network. All three compounds exhibit good catalytic abilities for the cyanosilylation of aldehyde.

Chiral porous metal–organic frameworks containing μ-oxo-bis[Ti(salan)] units for asymmetric cyanation of aldehydes

Two chiral porous metal–organic frameworks containing μ-oxo-bis[Ti(salan)] dimers are constructed and shown to be efficient and recyclable heterogeneous catalysts for asymmetric cyanation reaction of aldehydes.