Porous Metalloporphyrinic Frameworks Constructed from Metal 5,10,15,20-Tetrakis(3,5-biscarboxylphenyl)porphyrin for Highly Efficient and Selective Catalytic Oxidation of Alkylbenzenes

Cobalt and nitrogen co-doped hollow periodic mesoporous organosilica spheres activated by potassium chloride for selective oxidation of ethylbenzene

Enhancing the exposure of metal active sites and maximizing metal atom utilization are critical challenges in heterogeneous catalysis. To solve these issues, heterogeneous catalysts are usually activated by chemicals. Herein, potassium chloride (KCl) was used as an activator to prepare cobalt-nitrogen co-doped (Co-Nx) hollow periodic mesoporous organosilica spheres (Co-Nx/HPMOs-KCl). Co-Nx/HPMOs-KCl showed outstanding catalytic activity for the selective oxidation of ethylbenzene to acetophenone, with a conversion of up to 94.0% for ethylbenzene and a high selectivity of 98.4% towards acetophenone. Additionally, Co-Nx/HPMOs-KCl maintained excellent catalytic performance for the oxidation of ethylbenzene after six cycles. The excellent performance of Co-Nx/HPMOs-KCl was attributed to the activation of KCl, which increased the specific surface area of the catalyst and thus facilitated the exposure of more metal active sites. After the removal of unstable metal species through further acid treatment, the remaining metal active sites were thus fully exposed and stably embedded in the framework of the hollow periodic mesoporous organosilica spheres (HMPOs). This work presents an efficient catalyst and offers new insights for the improvement of heterogeneous catalysts.

Recent Developments in Porphyrin-Based Metal-Organic Framework Materials for Water Remediation under Visible-Light Irradiation

Access to clean drinking water is a basic requirement, and eliminating pollutants from wastewater is important for saving water ecosystems. The porous structure and surface characteristics of metal-organic frameworks (MOFs) can function as a perfect scaffold for removing toxic compounds from wastewater. Porphyrins are promising building blocks for constructing MOFs. Porphyrin-based metal-organic frameworks (P-MOFs) have been fabricated using porphyrin ligands, metal clusters, or ions. These materials can harvest light from a wide region of the solar spectrum, and their framework morphology and physicochemical properties can be controlled by changing their peripheral subunits or metal ions. These porous crystalline materials have generated interest because of their distinctive characteristics, including large permanent porosity, interesting surface morphology, broad conformational diversity, high photostability, and semiconducting nature. This article discusses the recent progress and usefulness of P-MOFs. The fabrication procedures of P-MOFs are discussed, followed by the adsorptive and photocatalytic removal of contaminants from wastewater. The relationships between the geometries of P-MOFs and their light-harvesting and charge-transfer mechanisms for the photocatalytic degradation of pollutants are highlighted. Finally, some future perspectives and obstacles in the photodegradation usage of P-MOFs are discussed, along with feasible research directions to standardize efficient photocatalysts for improved photodegradation for water treatment.

Porphyrin-Based Metal-Organic Framework Materials: Design, Construction, and Application in the Field of Photocatalysis

Metal-organic frameworks (MOFs) are a novel category of porous crystalline materials with an exceptionally high surface area and adjustable pore structure. They possess a designable composition and can be easily functionalized with different units. Porphyrins with conjugated tetrapyrrole macrocyclic structures can absorb light from ultraviolet to visible light regions, and their structures and properties can be facilely regulated by altering their peripheral groups or central metal ions. Porphyrin-based MOFs constructed from porphyrin ligands and metal nodes combine the unique features of porphyrins and MOFs as well as overcoming their respective limitations. This paper reviewed the design and construction, light absorption and charge transfer pathways, and strategy for improving the photocatalytic performance of porphyrin-based MOFs, and highlighted the recent progress in the field of CO2 reduction, hydrogen evolution, organic synthesis, organic pollutant removal, and nitrogen fixation. The intrinsic relationships between the structure and the property of porphyrin-based MOFs received special attention, especially the relationships between the arrangements of porphyrin ligands and metal nods and the charge transfer mechanism. We attempted to provide more valuable information for the design and construction of advanced photocatalysts in the future. Finally, the challenges and future perspectives of the porphyrin-based MOFs are also discussed.

Coordination Defect-Induced Frustrated Lewis Pairs in Polyoxo-metalate-Based Metal-Organic Frameworks for Efficient Catalytic Hydrogenation

Precise control of the structure and spatial distance of Lewis acid (LA) and Lewis base (LB) sites in a porous system to construct efficient solid frustrated Lewis pair (FLP) catalyst is vital for industrial application but remains challenging. Herein, we constructed FLP sites in a polyoxometalate (POM)-based metal-organic framework (MOF) by introducing coordination-defect metal nodes (LA) and surface-basic POM with abundant oxygen (LB). The well-defined and unique spatial conformation of the defective POM-based MOF ensure that the distance between LA and LB is at ~4.3 Å, a suitable distance to activate H2 . This FLP catalyst can heterolytically dissociate H2 into active Hδ- , thus exhibiting high activity in hydrogenation, which is 55 and 2.7 times as high as that of defect-free POM-based MOF and defective MOF without POM, respectively. This work provides a new avenue toward precise design multi-site catalyst to achieve specific activation of target substrate for synergistic catalysis.

Ligand Conformation Fixation Strategy for Expanding the Structural Diversity of Copper-Tricarboxylate Frameworks and C2H2 Purification Performance Studies

Structural and functional expansion of metal-organic frameworks (MOFs) is fundamentally important because it not only enriches the structural chemistry of MOFs but also facilitates the full exploration of their application potentials. In this work, by employing a dual-site functionalization strategy to lock the ligand conformation, we designed and synthesized a pair of biphenyl tricarboxylate ligands bearing dimethyl and dimethoxy groups and fabricated their corresponding framework compounds through coordination with copper(II) ions. Compared to the monofunctionalized version, introduction of two side groups can significantly fix the ligand conformation, and as a result, the dual-methoxy compound exhibited a different network structure from the mono-methoxy counterpart. Although only one almost orthogonal conformation was observed for the two ligands, their coordination framework compounds displayed distinct topological structures probably due to different solvothermal conditions. Significantly, with a hierarchical cage-type structure and good hydrostability, the dimethyl compound exhibited promising practical application value for industrially important C₂H₂ separation and purification, which was comprehensively demonstrated by equilibrium/dynamic adsorption measurements and the corresponding Clausius-Clapeyron/IAST/DFT theoretical analyses.

Metalloporphyrin Metal–Organic Frameworks: Eminent Synthetic Strategies and Recent Practical Exploitations

The emergence of metal–organic frameworks (MOFs) in recent years has stimulated the interest of scientists working in this area as one of the most applicable archetypes of three-dimensional structures that can be used as promising materials in several applications including but not limited to (photo-)catalysis, sensing, separation, adsorption, biological and electrochemical efficiencies and so on. Not only do MOFs have their own specific versatile structures, tunable cavities, and remarkably high surface areas, but they also present many alternative procedures to overcome emerging obstacles. Since the discovery of such highly effective materials, they have been employed for multiple uses; additionally, the efforts towards the synthesis of MOFs with specific properties based on planned (template) synthesis have led to the construction of several promising types of MOFs possessing large biological or bioinspired ligands. Specifically, metalloporphyrin-based MOFs have been created where the porphyrin moieties are either incorporated as struts within the framework to form porphyrinic MOFs or encapsulated inside the cavities to construct porphyrin@MOFs which can combine the peerless properties of porphyrins and porous MOFs simultaneously. In this context, the main aim of this review was to highlight their structure, characteristics, and some of their prominent present-day applications.

Tailored Inorganic-Organic Architectures via Metalloligands

This article discusses the design principles and strategies and the structural outcome of various supramolecular architectures constructed by utilizing well-defined coordination complexes as the metalloligands. We have included selected examples of metalloligands, offering either pyridyl or arylcarboxylic acid groups as the appended functional groups, for illustrating the construction of their supramolecular architectures. Both geometrical position and the number of the appended functional groups emerging from a metalloligand were found to critically regulate the structural aspects and dimensionality of the resultant material. The article concludes by delineating the structure-directing lessions as well as the potential applications of the metalloligand-based supramolecular architectures for the generation of next-level materials.

A Keggin-type polyoxometalate-based metal-organic complex as a highly efficient heterogeneous catalyst for the selective oxidation of alkylbenzenes

The direct oxidation of C-H bonds in organic materials into necessary oxygen-containing compounds under mild conditions has attracted increasing attention. A Keggin-type polyoxometalate-based metal-organic complex (MOC), [CuII4Cu^I(H₂trz)₄(C₂O₄)(H₂O)₄(H₃PW_11.18CuII0.82O₄₀)]·8H₂O (1) (H₃trz = 1,2,4-triazole), was designed and synthesized under hydrothermal conditions, and was structurally characterized by single crystal X-ray diffraction, PXRD, IR spectroscopy, TGA, and XPS. Complex 1 is a 3D 4,6,8-connected architecture derived from [Cu₅(H₂trz)₄(C₂O₄)₂(H₂O)₂]_n units and [PW_11.18Cu_0.82O₄₀]^6- anions, which can catalytically oxidize various types of alkylbenzenes. Gas chromatographic analysis showed that complex 1 as a heterogeneous catalyst could effectively catalyze the oxidation of diphenylmethane with 93% conversion and 99% selectivity within 6 h. In addition, the conversion for the catalytic oxidation of ethylbenzene was 96% with 99% selectivity. Compared with some reported catalysts, complex 1 exhibited a better catalytic effect and lower reaction time. Meanwhile, the catalytic oxidation of other benzyl derivatives with complex 1 was also investigated, which indicated that complex 1 possessed excellent catalytic performance.

A two-dimensional Bi-based porphyrin metal–organic framework photocatalyst for white light-driven selective oxidation of sulfides

A single crystal of a Bi-based porphyrin metal–organic framework was synthesized by a hydrothermal method. It exhibited significant photocatalytic activity for the selective oxidation of sulfides, maintaining high activity after 10 catalytic cycles.

Immobilizing a homogeneous manganese catalyst into MOF pores for α-alkylation of methylene ketones with alcohols

An encapsulation strategy via nano-confinement of a homogeneous manganese–phenanthroline complex into MOF pores selectively produced functionalized branched ketones.

A self-assembly solvothermal synthesis of SiMoVn@[Cu6O(TZI)3(H2O)6]4·nH2O for the efficient selective oxidation of various alkylbenzenes

A series of SiMoVn@rht-MOF-1 were isolated via a one-pot self-assembly solvothermal synthesis, exhibiting effective catalytic activity and excellent recyclability.

Catalysis in Single Crystalline Materials: From Discrete Molecules to Metal-Organic Frameworks

Catalysis is one of the key techniques for people's modern life. It has created numerous essential chemicals such as biomedicines, agricultural chemicals and unique materials. Heterogeneous catalysis is the new emerging method with reusable catalysts. Among heterogenous catalysis patterns developed so far, single crystalline catalysis has become the promising one owing to its high catalytic density and selectivity resulted by the inherent porosity, orderliness of the lattices and permeability. These crystalline catalysts could be used in various reactions such as photo-dimerization, Diels-Alder reaction, CO₂ transformation and so on. In this review, we highlighted the reported works about the single crystalline catalysts. Both discrete small molecules and metal-organic frameworks (MOFs) have been used to prepare single crystals for catalysis. For discrete molecules based crystalline catalysts, coordinated and covalent molecules have been used. There were more catalytic modes in crystalline MOF catalysts. Three patterns were identified in this review: single crystalline MOFs i) without catalytic sites, ii) with inherent catalytic features and iii) with introducing catalytic units by post synthetic modification. Based on these examples, this review committed to provide the inspirations for the further design and application of single crystalline materials.

A historical perspective on porphyrin-based metal-organic frameworks and their applications

Porphyrins are important molecules widely found in nature in the form of enzyme active sites and visible light absorption units. Recent interest in using these functional molecules as building blocks for the construction of metal-organic frameworks (MOFs) have rapidly increased due to the ease in which the locations of, and the distances between, the porphyrin units can be controlled in these porous crystalline materials. Porphyrin-based MOFs with atomically precise structures provide an ideal platform for the investigation of their structure-function relationships in the solid state without compromising accessibility to the inherent properties of the porphyrin building blocks. This review will provide a historical overview of the development and applications of porphyrin-based MOFs from early studies focused on design and structures, to recent efforts on their utilization in biomimetic catalysis, photocatalysis, electrocatalysis, sensing, and biomedical applications.

Preparation and characterization of a copper oxide nanoparticle-supported red-mud catalyst for liquid phase oxidation of ethyl benzene to acetophenone

In this study, liquid phase oxidation of ethyl benzene to acetophenone was widely investigated using a new recyclable supported catalyst of CuO nanoparticles impregnated over activated red-mud (CuO_AARM).

Photonic Switching Porous Organic Polymers toward Reversible Control of Heterogeneous Photocatalysis

Sonogashira-Hagihara coupling reaction of photoswitchable dithienylethene (AEDTE) with metal-free 5,10,15,20-tetrakis(4-iodophenyl)porphyrin and its metal derivatives (MTIPP, M = H₂, Zn(II), Fe(II)) results in three porous organic polymers (POPs) including AEDTE-H₂TIPP-POP, AEDTE-ZnTIPP-POP, and AEDTE-FeTIPP-POP. The morphology, components, and structures of newly obtained POPs have been examined by a range of spectroscopic and microscopic techniques including infrared spectroscopy (IR), solid-state UV-vis diffuse reflectance spectroscopy, thermogravimetric analysis (TGA), powder X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The porous structures have been estimated by nitrogen and carbon dioxide sorption isotherms at 77 and 196 K, respectively. The open-AEDTE-H₂TIPP-POP with AEDTE in an open form was revealed to be an effective and stable heterogeneous photocatalyst for visible light-driven oxidation of N-methylpyridinium salts possibly because of its relatively large specific surface area. In particular, a proof-of-concept of photoswitchable POP photocatalysts has been established using different light irradiation upon open-AEDTE-H₂TIPP-POP to control its heterogeneous photocatalytic behaviors because of the adjustment over the electron transfer process and porous structures through photoisomerization of AEDTE. The present result highlights the bright perspective of photoswitching POPs in the field of materials chemistry and catalysis community.

Identification of the activity source of CO2 electroreduction by strategic catalytic site distribution in stable supramolecular structure system

Identification of the real catalytic site in CO₂ reduction reaction (CO₂RR) is critical for the rational design of catalysts and the understanding of reactive mechanisms. In this study, the catalytic activity of pyridine-containing materials was for the first time structurally demonstrated in CO₂RR by crystalline supramolecular coordination compounds model system. The system consists of three stable supramolecular coordination compounds (Ni-TPYP, Ni-TPYP-1 and Ni-TPP) with different numbers (4, 2 and 0) of active pyridine groups (i.e. uncoordinated pyridine nitrogen atoms). The electrocatalytic test results show that with the decrease of the number of active pyridine groups, the CO₂RR performance is gradually reduced, mainly showing the reduction of highest FE_CO (99.8%, 83.7% and 25.6%, respectively). The crystallographic, experimental and theoretical evidences prove that the CO₂RR activity is more likely derived from uncoordinated pyridine nitrogen than the electrocatalytic inert metal nickel in porphyrin center. This work serves as an important case study for the identification of electrocatalytic activity of pyridine-containing materials in CO₂RR by simple supramolecular model system.

Full use of factors promoting catalytic performance of chitosan supported manganese porphyrin

In order to make full use of the impact of internal and external factors on the performance of title catalyst for ethyl benzene oxidation, the key internal influencing factors on the catalytic performance were modulated by coordinating and grafting manganese porphyrin to mesoporous and macroporous chitosan, and the important external factors (i.e. oxidation reaction conditions) were optimized using Response Surface Methodology. Under the Response Surface Methodology optimized oxidation reaction conditions (176.56 °C, 0.59 MPa, and 0.25 mg amount of manganese porphyrin), the catalyst could be used at least five times. The ethyl benzene conversion, catalyst turnover numbers, and yields reached up to 51.2%, 4.37 × 106 and 36.4% in average, respectively. Compared with the other optimized oxidation reaction conditions, the corresponding values increased 17%, 26% and 53%. Relative to the manganese porphyrin, the catalytic performance and efficiency of the immobilized catalyst had notably increased.

Metal-Organic Framework-Based Catalysts with Single Metal Sites

Metal-organic frameworks (MOFs) are a class of distinctive porous crystalline materials constructed by metal ions/clusters and organic linkers. Owing to their structural diversity, functional adjustability, and high surface area, different types of MOF-based single metal sites are well exploited, including coordinately unsaturated metal sites from metal nodes and metallolinkers, as well as active metal species immobilized to MOFs. Furthermore, controllable thermal transformation of MOFs can upgrade them to nanomaterials functionalized with active single-atom catalysts (SACs). These unique features of MOFs and their derivatives enable them to serve as a highly versatile platform for catalysis, which has actually been becoming a rapidly developing interdisciplinary research area. In this review, we overview the recent developments of catalysis at single metal sites in MOF-based materials with emphasis on their structures and applications for thermocatalysis, electrocatalysis, and photocatalysis. We also compare the results and summarize the major insights gained from the works in this review, providing the challenges and prospects in this emerging field.

Metalloporphyrinic metal-organic frameworks: Controlled synthesis for catalytic applications in environmental and biological media

Recently, as a new sub-family of porous coordination polymers (PCPs), porphyrinic-MOFs (Porph-MOFs) with biomimetic features have been developed using porphyrin macrocycles as ligands and/or pillared linkers. The control over the coordination of the porphyrin ligand and its derivatives however remains a challenge for engineering new tunable Porph-MOF frameworks by self-assembly methods. The key challenges exist in the following respects: (i) collapse of the large open pores of Porph-MOFs during synthesis, (ii) deactivation of unsaturated metal-sites (UMCs) by axial coordination, and (iii) the tendency of both coordinated moieties (at peripheral meso- and beta-carbon sites) and the N₄-pyridine core to coordinate with metal cations. In this respect, this review covers the advances in the design of Porph-MOFs relative to their counterpart covalent organic frameworks (Porph-COFs). The potential utility of custom-designed porphyrin/metalloporphyrins ligands is highlighted. Synthesis strategies of Porph-MOFs are also illustrated with modular design of hybrid guest@host composites (either Porph@MOFs or guest@Porph-MOFs) with exceptional topologies and stability. This review summarizes the synergistic benefits of coordinated porphyrin ligands and functional guest molecules in Porph-MOF composites for enhanced catalytic performance in various redox applications. This review shed lights on the engineering of new tunable hetero-metals open active sites within (metallo)porphyrin-MOFs as out-of-the-box platforms for enhanced catalytic processes in chemical and biological media.

The synthesis and applications of chiral pyrrolidine functionalized metal–organic frameworks and covalent-organic frameworks

Proline based ligands show versatile functionality to construct chiral MOFs and COFs; meanwhile, the resulted frameworks are potential materials for enantioselective adsorption and asymmetric catalysis.

Visible-light-driven self-coupling and oxidative dehydrogenation of amines to imines via a Mn(ii)-based coordination polymer

The direct synthesis of various imines through visible-light-driven photocatalytic self-coupling and dehydrogenation of amines was achieved using a novel coordination polymer.

Acetylacetone as an oxygen activator to improve efficiency for aerobic oxidation of toluene and its derivatives by using cobalt meso-tetraphenylporphyrin

An efficient system comprising acetylacetone and cobalt tetraphenylporphyrin was developed for the aerobic oxidation of toluene and its derivatives, in which acetylacetone served as the key initiator of the free radical in activating dioxygen.

Elucidating J-Aggregation Effect in Boosting Singlet-Oxygen Evolution Using Zirconium-Porphyrin Frameworks: A Comprehensive Structural, Catalytic, and Spectroscopic Study

Metal-organic frameworks (MOFs) are powerful toolkits to directly correlate structure-function relationships due to their well-defined structures. In this work, 5,15-di(3,4,5-trihydroxyphenyl)porphyrin (DTPP) and 5,10,15,20-tetra(3,4,5-trihydroxyphenyl)porphyrin (TTPP) are reacted with zirconium ions to afford two MOFs (Zr-DTPP and Zr-TTPP) with acid and base tolerance in the pH range of 1.0-14.0. Powder X-ray diffraction investigation combined with Rietveld refinement reveals the J-aggregated porphyrin building blocks confined by benzene-1,2,3-trisolate-zirconium chains in the newly prepared Zr-DTPP. Electron spin-resonance, singlet-oxygen determination, and sulfides oxidation experiments demonstrate a much better singlet-oxygen evolution of J-aggregated Zr-DTPP than that of unaggregated Zr-TTPP reported previously, in good contrast to the weaker photocatalytic capability disclosed for DTPP than that for TTPP in solution, consummating the theory of photosensitizer J-aggregation in boosting heterogeneous photoinduced singlet-oxygen generation.

Syntheses, structures, and magnetic properties of mixed-ligand complexes based on 3,6-bis(benzimidazol-1-yl)pyridazine

Six new metal-organic coordination polymers (CPs) [Ni(L)(2,5-TDC)(H2O)] n (1), [Ni(L)(1,3-BDC)(H2O)] n (2), [Ni(L)(1,4-BDC)(H2O)] n (3), [Mn(L)(2,5-TDC)(H2O)] n (4), [Mn(L)(2,6-PYDC)(H2O)] n (5) and [Mn(L)(1,4-NDC)] n (6) were achieved by reactions of the corresponding metal salt with mixed organic ligands (L = 3,6-bis(benzimidazol-1-yl)pyridazine, 2,5-H2TDC = thiophene-2,5-dicarboxylic acid, 1,3-H2BDC = isophthalic acid, 1,4-H2BDC = terephthalic acid, 2,6-H2PYDC = pyridine-2,6-dicarboxylic acid, 1,4-H2NDC = naphthalene-1,4-dicarboxylic acid) under solvothermal condition. CPs 1-6 were characterized by single-crystal X-ray diffraction, IR, TG, XRD and elemental analyses. Their structures range from the intricate 3D CPs 1, 3, 4 and 6 to the 2D coordination polymer 2 and the infinite 1D chain 5. The CPs 1-4 and 6 underlying networks were classified from the topological viewpoint, disclosing the distinct sql (in 1), pcu (in 3 and 6), new topology (in 2), and dia (in 4) topological nets. Moreover, analysis of thermal stability shows that they had good thermal stability. Finally, magnetic properties of CPs 1-6 have been studied, the results showed that complex 2 had ferromagnetic coupling and complexes 1, 3-6 were antiferromagnetic.