Hydroxo Iron(III) Sites in a Metal-Organic Framework: Proton-Coupled Electron Transfer and Catalytic Oxidation of Alcohol with Molecular Oxygen

Tuning Ni-Pyrazolate Frameworks by Post-Synthetic Fe-Incorporation for Oxidase-Mimicking H2 O2 Activation

The introduction of iron ionic sites by metal exchange of defective homometallic nickel pyrazolate frameworks generates non-precious, Earth-abundant, first-row heterometallic Fe/Ni-pyrazolate frameworks. The Fe incorporation at the Ni nodes of the framework allows to control the hydrogen peroxide activation, minimizing its decomposition and O2 liberation, occurring at the homometallic Ni nodes. The generation of Fe-OH reactive oxygen species at the heterometallic Fe/Ni nodes is demonstrated by the higher activity in the proof-of-concept oxidation of 1-phenylethanol to acetophenone in an aqueous medium.

A sustainable protocol for selective alcohols oxidation using a novel iron-based metal organic framework (MOF-BASU1)

The selective oxidation of active and inactive alcohol substrates is a highly versatile conversion that poses a challenge in controlling the functionality and adjustments on MOFs. On the other hand, it offers an attractive opportunity to expand their applications in designing the next generation of catalysts with improved performance. Herein, a novel iron-based MOF containing sulfonamide (MOF-BASU1) has been fabricated by the reaction of 1,3-benzene disulfonylchloride linker and FeCl3·6H2O. Based on the results, the active surface area of the synthesized MOF is large, which highlights its unique catalytic activity. Optimum conditions were reached after 0.5-2 h, with 15 mg loading of the synthesized MOF under optimal conditions. Furthermore, the turnover frequency was 18-77.6 h-1, which is comparable to values previously reported for this process. Overall, the high catalytic activity observed for MOF-BASU1 might be because of the obtained high surface area and the Lewis acidic Fe nodes. Furthermore, the MOF-BASU1 revealed a remarkable chemoselectivity for aldehydes in the presence of aliphatic alcohols. Overall, the high product yields, facile recovery of nanocatalysts, short reaction times, and broad substrate range make this process environmentally friendly, practical, and economically justified.

Anthraquinone-Based Metal-Organic Frameworks as a Bifunctional Photocatalyst for C-H Activation

Metal-organic frameworks (MOFs) have gained attention as multifunctional catalytic platforms, allowing us to gain important insights into synergistically activating both C-H bonds and oxygen for improving oxidation. Herein, by ingenious incorporation of anthraquinone, we report an anthraquinone-based MOF as a bifunctional heterogeneous photocatalytic platform to simultaneously activate inert C(sp³)-H bonds and oxygen for C-H bond oxidation. Making use of the rigid framework with the fixation and isolation effect, both a great chemical stability and bifunctional synergistic photocatalytic effects were obtained through the immobilization of anthraquinone into a MOF. Importantly, while decorating two carboxyl groups on anthraquinone, the carbonyl groups of anthraquinone photosensitizers were not involved in coordinating the self-assembly and orderly arranged on the wall of channels that were constructed through a π-π interaction between the anthraquinone moieties in the adjacent layers, which was beneficial to form and stabilize the excited-state radical intermediates in the molecule-fenced channels, and the close proximity between the catalytic sites and the substrates to abstract a hydrogen atom from the substrate through the hydrogen atom transfer process aimed at activating the inertness of C-H bonds. Moreover, high-density-distributed anthraquinone dyes in the confined channels would activate oxygen to form singlet oxygen (¹O₂) through an energy transfer pathway, further promoting inert C(sp³)-H bond oxidation efficiency. Under visible light irradiation, this anthraquinone-based MOF was successfully applied to explore activation and oxidation of a series of substrates containing benzylic C(sp³)-H bonds in the presence of air or oxygen to produce the corresponding carbonyl products. This bifunctional photocatalytic platform based on a heterogeneous MOF provides an available catalytic avenue to develop a scalable and sustainable synthetic strategy using green and sustainable oxygen as the potent oxidant.

Superoxide Ion and Singlet Oxygen Photogenerated by Metalloporphyrin-Based Metal-Organic Frameworks for Highly Efficient and Selective Photooxidation of a Sulfur Mustard Simulant

The exploration of highly efficient materials for the degradation of chemical warfare agents has been a longstanding task for preventing human exposure. Herein, we report a series of metal-organic frameworks (MOFs) M-TCPP-La based on metallo-tetra(4-carboxyphenyl)porphyrin and La^III, which were applied to selectively oxidize 2-chloroethyl ethyl sulfide (CEES, a sulfur mustard simulant) as heterogeneous photocatalysts. After irradiation from a commercial blue light-emitting diode (LED), both superoxide ion and singlet oxygen were generated by M-TCPP-La and involved in selective oxidization of CEES to 2-chloroethyl ethyl sulfoxide (CEESO). Notably, a very short half lifetime (2.5 min) was achieved using Fe-TCPP-La as the photocatalyst. In comparison to currently utilizing singlet oxygen and hydrogen peroxide as oxidizing agents, this work employing both singlet oxygen and superoxide ion represents a new and effective strategy of detoxification of mustard gas.

Metal-organic frameworks with the gyroid surface: structures and applications

Gyroid materials have received considerable attention from scientists due to their beautiful structures and advanced functions. On the other side, metal-organic frameworks are inorganic-organic hybrid crystalline porous materials with atomic precision, and can provide good structural models and rich topologies for gyroid materials. In this review, we will briefly introduce the structures of gyroid metal-organic frameworks and their topologies. In addition, their applications in gas adsorption, catalysis, sensors, and luminescent materials are also discussed in detail.

Molecular Cage Promoted Aerobic Oxidation or Photo-Induced Rearrangement of Spiroepoxy Naphthalenone

Herein, we report a Pd4L2-type molecular cage (1) and catalyzed reactions of spiroepoxy naphthalenone (2) in water, where selective formation of 2-(hydroxymethyl)naphthalene-1,4-dione (3) via aerobic oxidation, or 1-hydroxy-2-naphthaldehyde (4) via photo-induced rearrangement under N2 have been accomplished. Encapsulation of four molecules of guest 2 within cage 1, i.e., (2)4⊂1, has been confirmed by NMR, and a final host-guest complex of 3⊂1 has also been determined by single crystal X-Ray diffraction study. While the photo-induced ring-opening isomerization from 2 to 4 are known, appearance of charge-transfer absorption on the host-guest complex of (2)4⊂1 allows low-power blue LEDs irradiation to promote this process.

A New Coumarin-Acridone Compound as a Fluorescence Probe for Fe3+ and Its Application in Living Cells and Zebrafish

A new coumarin-acridone fluorescent probe S was designed and synthesized, and the structure was confirmed with ¹H/¹³C NMR spectrometry, single-crystal X-ray diffraction, and high-resolution mass spectrometry. This probe has high sensitivity and selectivity for Fe³⁺ over other testing metal ions at 420 or 436 nm in acetonitrile-MOPS (3-Morpholinopropanesulfonic Acid) buffer solution (20.0 μM, pH = 6.9, 8:2 (v/v)). Under physiological conditions, the probe displayed satisfying time stability with a detection limit of 1.77 µM. In addition, probe S was successfully used to detect intracellular iron changes through a fluorescence-off mode, and the imaging results of cells and zebrafish confirmed their low cytotoxicity and satisfactory cell membrane permeability, as well as their potential biological applications.

One-Step Construction of a Hollow Au@Bimetal-Organic Framework Core-Shell Catalytic Nanoreactor for Selective Alcohol Oxidation Reaction

Hollow core-shell catalytic nanoreactors have received tremendous attention due to their high mass transfer in catalysis applications. Herein, we present a novel type of well-arranged, hollow core-shell nanoreactors featured with a bimetallic porous Zn/Ni-MOF-2 shell and a tiny Au nanoparticle core. The well-designed hollow Au@Zn/Ni-MOF-2 nanoreactors were constructed through the strategy of a facile one step from a rare crystal-structure transformation without any additional template. These nanoreactors exhibit outstanding multifunctional catalysis for a broad range of alcohol oxidation under the green oxidant environment. Moreover, such hollow nanoreactors show excellent recyclability toward the selective alcohol oxidation. These findings might provide a promising platform for a general construct of various metal-organic framework-based hollow core-shell nanostructures and further highly augmented catalytic applications.

On the limit of proton-coupled electronic doping in a Ti(iv)-containing MOF

Ti^IV-containing metal–organic frameworks are known to accumulate electrons in their conduction bands, accompanied by protons, when irradiated in the presence of alcohols. The archetypal system, MIL-125, was recently shown to reach a limit of 2e⁻ per Ti₈ octomeric node. However, the origin of this limit and the broader applicability of this unique chemistry relies not only on the presence of Ti^IV, but also access to inorganic inner-sphere Lewis basic anions in the MOF nodes. Here, we study the loading of protons and electrons in MIL-125, and assess the thermodynamic limit of doping these materials. We find that the limit is determined by the reduction potential of protons: in high charging regimes the MOF exceeds the H⁺/H₂ potential. Generally, we offer the design principle that inorganic anions in MOF nodes can host adatomic protons, which may stabilize meta-stable low valent transition metals. This approach highlights the unique chemistry afforded by MOFs built from inorganic clusters, and provides one avenue to developing novel catalytic scaffolds for hydrogen evolution and transfer hydrogenation.

Photo-promoted doping of MIL-125 is limited by the potential of MOF-bound protons exceeding the hydrogen evolution reaction.