Assembling Porphyrins into Extended Network Structures by Employing Aromatic Dicarboxylates: Synthesis, Metal Exchange, and Heterogeneous Catalytic Studies

Fixing CO2 under Atmospheric Conditions and Dual Functional Heterogeneous Catalysis Employing Cu MOFs: Polymorphism, Single-Crystal-to-Single-Crystal (SCSC) Transformation and Magnetic Studies

New copper compounds, [Cu(C14H8O6)(C10H8N2)(H2O)] (1), [Cu(C14H8O6)(C10H8N2)(H2O)]·(C3H7ON)2 (2), [Cu(C14H8O6)(C10H8N2)(H2O)2]·(C3H7ON) (3), [Cu(C14H8O6)(C10H8N4)] (4), and [Cu(C14H8O6)(C10H8N4)]·(H2O) (5), were prepared employing 2,5-bis(prop-2-yn-1-yloxy)terephthalic acid (2,5-BPTA) as the primary ligand and 4,4'-bipyridine (1-3) and 4,4'-azopyridine (4-5) as the secondary ligands. Single-crystal studies indicated that compounds 1-4 have two-dimensional layer structures and compound 5 has a three-dimensional structure. Compounds 1-3 were isolated from the same reaction mixture but by varying the time of reaction. The framework structures of compounds 1-3 are similar and may be considered as polymorphic structures. Compounds 4 and 5 can also be considered polymorphic with a change in dimensionality of the structure. Compounds 1-3 can be formed through a single-crystal-to-single-crystal transformation under a suitable solvent mixture. The Cu center was explored for the Lewis acid-catalyzed cycloaddition reaction of epoxide and CO2 under ambient conditions in a solventless condition and also for the synthesis of propargylamine derivatives by three-component coupling reactions (A3 coupling) in a DCM medium. The Lewis basic functionality of the MOF (-N═N- group) has been explored for the Henry reaction (aldol condensation) in a solventless condition. In all of the catalytic reactions, good yields and recyclability were observed. The magnetic studies indicated that compounds 1 and 4 have antiferromagnetic interactions and compound 5 has ferromagnetic interactions. The present studies illustrated the rich diversity that the copper-containing compounds exhibit in extended framework structures.

Highly Selective MOF-Based Turn-Off Luminescence Detection of Hg2+ Ions in an Aqueous Medium and Its Dual Functional Catalytic Activity toward Aldol Condensation and β-Enamination Reactions

A new organic ligand, 5-(carboxyformamido)isophthalic acid (5-CFIA), was prepared and employed for the synthesis of two compounds [M₃(C₁₀H₄O₇N₁)₂(8H₂O)]·H₂O (M = Cd, Mn). The compounds have three-dimensionally extended structures. Both the compounds were found to be luminescent at room temperature. The luminescence nature was exploited for the detection of Hg²⁺ ions in an aqueous medium with good selectivity. The interactions between Hg²⁺ ions and the compounds quench the luminescence intensity and act as a turn-off sensor. Both the compounds exhibited low limits for the detection of Hg²⁺ ions and in the range mandated by the WHO. The interactions between Hg²⁺ ions and the compound involve the -NH group, which was probed using Raman and IR spectroscopic techniques. These studies provide important pointers toward the mechanism of this turn-off luminescence behavior. The compounds were explored for base-catalyzed aldol condensation and Lewis acid-promoted β-enaminoester formation reactions. The aldol condensation reaction uses the -NH functionality as a base. The studies indicate that the electron-withdrawing group produces products with higher yields. The β-enaminoester reaction uses the Lewis acid centers, and the studies reveal that the electron-withdrawing groups produce lesser yields of the products. The catalytic nature of the reaction and recyclability of the catalysts were also established. The catalytic reactions employ ethanol (aldol condensation) and no solvent (β-enaminoester), which suggests that the reactions are green and environmentally friendly. The Mn compound was observed to be anti-ferromagnetic.

Crystalline paramagnetic supramolecular 2D-polymer of the tetra(4-pyridyl)porphyrin and terbium(iii) complex

A new crystalline hybrid organic–inorganic two-dimensional supramolecular polymer of the tetra(4-pyridyl)porphyrin and terbium(iii) complex, TbIII(TMHD)3, has been obtained and investigated.

Supported metals on porous solids as heterogeneous catalysts for the synthesis of propargylamines

This perspective summarizes recent developments in the synthesis of propargylamines using porous solids (zeolites, MOFs and carbon) as supports/catalysts.

Metal–organic framework (MOF)-, covalent-organic framework (COF)-, and porous-organic polymers (POP)-catalyzed selective C–H bond activation and functionalization reactions

The review summarizes the state-of-the-art of C–H active transformations over crystalline and amorphous porous materials as new emerging heterogeneous (photo)catalysts.

Defect engineering: an effective tool for enhancing the catalytic performance of copper-MOFs for the click reaction and the A3 coupling

A series of Cu(i)-enriched and Lewis basic site-containing defect-engineering MOFs was investigated for significantly enhanced catalytic performance in the click reaction and the A³ coupling.

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.

Copper-based catalysts derived from salen-type ligands: synthesis of 5-substituted-1H-tetrazoles via [3+2] cycloaddition and propargylamines via A3-coupling reactions

Base-metal copper(ii) complexes derived from unsymmetrical salen-type ligands were designed and synthesized using ligands L¹H to L⁴H. These complexes were employed as catalysts for [3+2] cycloaddition and A³-coupling reactions.

Structural tuning of zinc–porphyrin frameworks via auxiliary nitrogen-containing ligands towards selective adsorption of cationic dyes

Three novel zinc–porphyrin MOFs have been synthesized by using versatile N-containing ligands. The open Watson–Crick pair in the interior surface in one Zn-MOF has been presented, which could endow the related MOF with excellent selective adsorption of dye molecules.

Transmetalation for Flexible Pendant-Armed Schiff-Base Macrocyclic Complexes Influenced by Halide Effects

Three 46-membered [2 + 2] pendant-armed Schiff-base macrocyclic dinuclear Cd^II and Cu^II complexes (2a, 2b, and 3b) and one 23-membered [1 + 1] Cu^II macrocycle 4a were prepared from the template-directed condensation reactions between 1,2-bis(2-aminoethoxy)-ethane and extended Cl-dialdehyde in the presence of CdX₂ and CuX₂ (X = Cl and Br), in which halide effects play important roles in the organization of final macrocyclic complexes in addition to the dominant influence of metal cations. Transmetalation was intensively studied among these Cd^II and Cu^II complexes with large and flexible macrocyclic ligands, including two previously synthesized dinuclear Zn^II macrocycles (1a and 1b). Our results indicate that Zn^II → Cu^II and Cd^II → Cu^II transmetalation proceeds more quickly than that from Cd^II to Zn^II, and all the processes are found to be irreversible. It is noted that a [2 + 2] heterodinuclear Cd^IIZn^II macrocyclic intermediate could be detected by ESI-MS together with [2 + 2] homodinuclear Cd^II and Zn^II macrocyclic complexes. Furthermore, distinct halide behavior was observed in the in situ Cd^II → Cu^II and Zn^II → Cu^II metal-ion exchange. That is to say, [2 + 2] macrocycles (1a and 2a) could be converted to [1 + 1] macrocycles 4a and 4b under the reflux condition in the case of CuCl₂, accompanied by the configurational transformation from half-folded dinuclear Zn^II and Cd^II to unfolded Cu^II macrocyclic skeleton. In contrast, CuBr₂ leads to a highly efficient transmetalation to corresponding [2 + 2] dinuclear Cu^II complex 3b from both 1b and 2b no matter the experimental condition used.

Development of Isostructural Porphyrin-Salen Chiral Metal-Organic Frameworks through Postsynthetic Metalation Based on Single-Crystal to Single-Crystal Transformation

The development of well-defined multimetallic porous metal-organic frameworks (MOFs) will add a new dimension to the application of MOF catalysis. From this perspective, the understanding and tailoring of the catalytic metal sites in MOFs are key fundamental challenges that could reveal the intrinsic potential of these materials. In this work, a series of porphyrin-salen chiral MOFs (ps-CMOFs 2-7) have been synthesized through postsynthetic metalation (PSMet) of the parent ps-CMOF via single-crystal to single-crystal transformation. Crystal structures of these ps-CMOF analogues revealed the same topological structure but varied metal entities compared to those of the parent framework. Note that the PSMet process involves three methods involving cation exchange at the nodes, cation exchange at the metalated porphyrin, and cation addition at the free porphyrin, which has been systematically investigated using single-crystal X-ray diffraction and other physicochemical methods. The N₂ adsorption tests, thermogravimetric analysis, and powder X-ray diffraction of 2-7 showed curves or patterns similar to those of 1, indicating the maintenance of the crystallinity, porosity, and thermal stability of the framework during the PSMet process. In addition, 2-7 showed distinctly improved adsorption capacities and isosteric heats of adsorption (Q_st) for CO₂ compared to those of their parent counterpart. Lastly, as a representative example of the ps-CMOF catalytic platform, 5 proved to be an efficient recyclable heterogeneous catalyst for the asymmetric addition reaction of CO₂ with epoxides under mild conditions. Furthermore, because of the constrained chiral environment within ps-CMOF, the enantioselectivity of this reaction appears to be dependent on substrate size.

Pseudopolymorphism based on 1D metallacyclic chains constructed from an angular zwitterionic ditopic diacid organic linker

Two pseudopolymorphs based on one dimensional metallacyclic chains display crystalline-form-dependent optical properties.