High-Valence Mn MOF Inspired by Laccase Mediators Enables Versatile Nature-Mimicking Catalysis

In nature, active Mn3+ -ligand complexes produced by laccase catalyzed oxidation can act as the low-molecular mass, diffusible redox mediators to oxidize the phenolic substrates overcoming the limitations of natural enzymes. Learning from the metal-ligand coordination of natural functional units, high-valence Mn metal-organic framework (Mn MOF) is constructed to simulate the catalysis in natural mediator system. Benefiting from the characteristics of nanoscale size, rich metal coordination unsaturated sites, and mixed valence state dominated by Mn(III), Nano Mn(III)-TP exhibits superior laccase-mimicking activity, whose Vmax (maximal reaction rate) is much higher than that of natural laccase. Referring to natural systems, relevant free radical experiments prove that the material induces the production of active oxygen species with the assistance of carboxylic acid, and active oxygen species further oxidize phenolic substrates. Based on its robust performances, the primary oxidative degradation of an emerging pollutant triclosan (TCS) is creatively applied, an important antiasthmatic medicine terbutaline sulfate (TBT) detection, and the synthesis of non-toxic and black near-natural dyes for dyeing. By simulating the essential mediators of natural enzymatic catalysis, an Mn MOF-based material that demonstrates multiple novel applications is successfully developed, which introduces a new reliable strategy for achieving versatile nature-mimicking catalysis.

Bis(2-butoxyethyl) Ether-Promoted O2-Mediated Oxidation of Alkyl Aromatics to Ketones under Clean Conditions

Conventional oxidation processes for alkyl aromatics to ketones employ oxidants that tend to generate harmful byproducts and cause severe equipment corrosion, ultimately creating critical environmental problems. Thus, in this study, a practical, efficient, and green method was developed for the synthesis of aromatic ketones by applying a bis(2-butoxyethyl) ether/O2 system under external catalyst-, additive-, and base-free conditions. This O2-mediated oxidation system can tolerate various functional groups and is suitable for large-scale synthesis. Diverse target ketones were prepared under clean conditions in moderate-to-high yields. The late-stage functionalization of drug derivatives with the corresponding ketones and one-pot sequential chemical conversions to ketone downstream products further broaden the application prospects of this approach.

Base-Assisted Aerobic C-H Oxidation of Alkylarenes with a Murdochite-Type Oxide Mg6MnO8 Nanoparticle Catalyst

Heterogeneously catalyzed aerobic oxidative C-H functionalization under mild conditions is a chemical process to obtain desired oxygenated products directly. Nanosized murdochite-type oxide Mg₆MnO₈ (Mg₆MnO₈-MA) was successfully synthesized by the sol-gel method using malic acid. The specific surface area reached up to 104 m² g^-1, which is about 7 times higher than those (2-15 m² g^-1) of Mg₆MnO₈ synthesized by previously reported methods. Mg₆MnO₈-MA exhibited superior catalytic performance to those of other Mn- and Mg-based oxides, including manganese oxides with Mn-O-Mn active sites for the oxidation of fluorene with molecular oxygen (O₂) as the sole oxidant under mild conditions (40 °C). The present catalytic system was applicable to the aerobic oxidation of various substrates. The catalyst could be recovered by simple filtration and reused several times without obvious loss of its high catalytic performance. The correlation between the reactivity and the pK_a of the substrates, basic properties of catalysts, and kinetic isotope effects suggest a basicity-controlled mechanism of hydrogen atom transfer. The ¹⁸O-labeling experiments, kinetics, and mechanistic studies showed that H abstraction of the hydrocarbon proceeds via a mechanism involving O₂ activation. The structure of Mg₆MnO₈ consisting of isolated Mn⁴⁺ species located in a basic MgO matrix plays an important role in the present oxidation.

Self-Driven Reactive Oxygen Species Generation via Interfacial Oxygen Vacancies on Carbon-Coated TiO2-x with Versatile Applications

The effective activation and utilization of O₂ have always been the focus of scientists because of its wide applications in catalysis, organic synthesis, life and medical science. Here, a novel method for activating O₂ spontaneously via interfacial oxygen vacancies on carbon-coated TiO_2-x to generate reactive oxygen species (ROS) with versatile applications is reported. The interfacial oxygen vacancies can be stabilized by the carbon layer and hold its intrinsic properties for spontaneous oxygen activation without light irradiation, while common surface oxygen vacancies on TiO_2-x are always consumed by the capture of H₂O to form the surface hydroxyls. Thus, O₂ absorbed at the interface of carbon and TiO_2-x can be directly activated into singlet oxygen (¹O₂) or superoxide radicals (·O₂^-), confirmed both experimentally and theoretically. These reactive oxygen species exhibit excellent performance in oxidation reactions and inhibition of MCF-7 cancer cells, providing new insight into the effective utilization of O₂ via oxygen vacancies on metal oxides.

Finely dispersed CuO on nitrogen-doped carbon hollow nanospheres for selective oxidation of sp3 C–H bonds

Selective oxidation of sp3 C–H bonds has been demonstrated using a novel nanocomposite, CuO/N-C-HNSs, as the catalyst.

Control of the Porosity in Manganese Trimer-Based Metal-Organic Frameworks by Linker Functionalization

Manganese complexes have attracted significant interest in chemical industries and academic research for their application as catalysts owing to their ability to attain a variety of oxidation states. Generally, sterically bulky ligands are required to isolate molecular homogeneous catalysts in order to prevent decomposition. Herein, we capitalize on the catalytic properties of Mn and circumvent the instability of these complexes through incorporation of Mn-atoms into porous crystalline frameworks, such as metal-organic frameworks (MOFs). MOFs are able to enhance the stability of these catalysts while also providing accessibility to the Mn sites for enhanced reactivity. We solvothermally synthesized two trinuclear Mn-based MOFs, namely [Mn₃O(BDC)₃(H₂O)₃]_n (Mn-MIL-88, where H₂BDC = benzene-1,4-dicarboxylic acid) and [Mn₃O(BDC-Me₄)₃(H₂O)₃]_n (Mn-MIL-88-Me₄, where H₂BDC-Me₄ = 2,3,5,6-tetramethylterephthalic acid). Through comprehensive single-crystal X-ray diffraction, spectroscopic, and magnetic studies, we revealed that both MOFs are in a Mn(II/III) mixed-valence state instead of the commonly observed Mn(III) oxidation state. Furthermore, the use of a methylated linker (BDC-Me₄) allowed access to permanent porosity in Mn-MIL-88-Me₄, which is an analogue of the flexible MIL-88 family, yielding a catalyst for alcohol oxidation.

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.

Controllable Sulfur, Nitrogen Co-doped Porous Carbon for Ethylbenzene Oxidation: The Role of Nano-CaCO3

Heteroatom-doped porous carbon materials have exhibited promising applications in various fields. In this work, sulfur, nitrogen co-doped carbon materials (SNCs) with abundant pore structure were prepared by pyrolysis of sulfur, nitrogen-containing porous organic polymers (POPs) mixed with nano-CaCO₃ at high temperature. Among the resultant materials, SNC-Ca-850 possesses a relatively high level of doped heteroatoms and exhibits an excellent catalytic performance for the selective oxidation of benzylic C-H bonds. It is noteworthy that nano-CaCO₃ increases the doped sulfur content in the synthesized carbon materials to a large extent and impacts the existence modes of sulfur. In addition, it enhances the porous structure and specific surface area of the resultant SNCs significantly. This work provides a viable strategy to promote the doping of sulfur into carbon materials during the pyrolysis process.

Computational Approach to Molecular Catalysis by 3d Transition Metals: Challenges and Opportunities

Computational chemistry provides a versatile toolbox for studying mechanistic details of catalytic reactions and holds promise to deliver practical strategies to enable the rational in silico catalyst design. The versatile reactivity and nontrivial electronic structure effects, common for systems based on 3d transition metals, introduce additional complexity that may represent a particular challenge to the standard computational strategies. In this review, we discuss the challenges and capabilities of modern electronic structure methods for studying the reaction mechanisms promoted by 3d transition metal molecular catalysts. Particular focus will be placed on the ways of addressing the multiconfigurational problem in electronic structure calculations and the role of expert bias in the practical utilization of the available methods. The development of density functionals designed to address transition metals is also discussed. Special emphasis is placed on the methods that account for solvation effects and the multicomponent nature of practical catalytic systems. This is followed by an overview of recent computational studies addressing the mechanistic complexity of catalytic processes by molecular catalysts based on 3d metals. Cases that involve noninnocent ligands, multicomponent reaction systems, metal-ligand and metal-metal cooperativity, as well as modeling complex catalytic systems such as metal-organic frameworks are presented. Conventionally, computational studies on catalytic mechanisms are heavily dependent on the chemical intuition and expert input of the researcher. Recent developments in advanced automated methods for reaction path analysis hold promise for eliminating such human-bias from computational catalysis studies. A brief overview of these approaches is presented in the final section of the review. The paper is closed with general concluding remarks.

Incorporation of a Ru complex into an amine-functionalized metal–organic framework for enhanced activity in photocatalytic aerobic benzyl alcohol oxidation

Encapsulation of [Ru(bpy)₃]²⁺ in the cavity of a metal–organic framework was found to enhance its activity in the photocatalytic aerobic oxidation of benzyl alcohol.

Aerobic conversion of benzylic sp3 C–H in diphenylmethanes and benzyl ethers to CO bonds under catalyst-, additive- and light-free conditions

Catalyst-, additive- and light-free aerobic conversion of benzylic C–H to CO bonds is, for the first time, reported.

Recent Advances in Homogeneous Metal-Catalyzed Aerobic C–H Oxidation of Benzylic Compounds

Csp3–H oxidation of benzylic methylene compounds is an established strategy for the synthesis of aromatic ketones, esters, and amides. The need for more sustainable oxidizers has encouraged researchers to explore the use of molecular oxygen. In particular, homogeneous metal-catalyzed aerobic oxidation of benzylic methylenes has attracted much attention. This account summarizes the development of this oxidative strategy in the last two decades, examining key factors such as reaction yields, substrate:catalyst ratio, substrate scope, selectivity over other oxidation byproducts, and reaction conditions including solvents and temperature. Finally, several mechanistic proposals to explain the observed results will be discussed.

Metal-Organic Frameworks Encapsulating Active Nanoparticles as Emerging Composites for Catalysis: Recent Progress and Perspectives

Beyond conventional porous materials, metal-organic frameworks (MOFs) have aroused great interest in the construction of nanocatalysts with the characteristics of catalytically active nanoparticles (NPs) confined into the cavities/channels of MOFs or surrounded by MOFs. The advantages of adopting MOFs as the encapsulating matrix are multifold: uniform and long-range ordered cavities can effectively promote the mass transfer and diffusion of substrates and products, while the diverse metal nodes and tunable organic linkers may enable outstanding synergy functions with the encapsulated active NPs. Herein, some key issues related to MOFs for catalysis are discussed. Then, state-of-the art progress in the encapsulation of catalytically active NPs by MOFs as well as their synergy functions for enhanced catalytic performance in the fields of thermo-, photo-, and electrocatalysis are summarized. Notably, encapsulation-structured nanocatalysts exhibit distinct advantages over conventional supported catalysts, especially in terms of the catalytic selectivity and stability. Finally, challenges and future developments in MOF-based encapsulation-structured nanocatalysts are proposed. The aim is to deliver better insight into the design of well-defined nanocatalysts with atomically accurate structures and high performance in challenging reactions.

A hierarchical flower-like hollow alumina supported bimetallic AuPd nanoparticle catalyst for enhanced solvent-free ethylbenzene oxidation

Currently, oxidation of alkylaromatics is considered as one of the most crucial chemical technologies to produce high added-value alcohols, ketones and carboxylic acids, due to its significant importance both in fine synthetic chemistry and in the academic field. In this work, a novel hierarchical marigold-like hollow alumina supported bimetallic AuPd nanoparticle catalyst was successfully fabricated and employed for highly efficient solvent-free ethylbenzene oxidation to produce acetophenone with the coexistence of both molecular oxygen and tert-butyl hydroperoxide as the oxidant and the initiator. The as-fabricated bimetallic AuPd nanocatalyst conferred a superior catalytic performance to the corresponding monometallic counterparts and commercial Al2O3 or solid Al2O3 microsphere supported AuPd ones, along with a high acetophenone selectivity of 88.2% at a conversion of 50.9% under mild reaction conditions (120 °C and oxygen pressure of 1.0 MPa), as well as an unprecedentedly high turnover frequency value of 46 768 h-1. Such exceptional efficiency of the catalyst was related to both the significant synergy between the Au-Pd atoms and strong metal-support interactions, and the unique hierarchical micro/nanostructure of the support being beneficial to the close contact of reactants with surface adsorption and reaction sites and easy product diffusion. Moreover, the present bimetallic AuPd catalyst was recyclable and stable. The developed approach is expected to offer exciting opportunities for designing other supported monometallic or bimetallic catalysts with various active components applied in heterogeneous catalysis.

Design of Single-Site Photocatalysts by Using Metal-Organic Frameworks as a Matrix

Single-site photocatalysts generally display excellent photocatalytic activity and considerably high stability compared with homogeneous catalytic systems. A rational structural design of single-site photocatalysts with isolated, uniform, and spatially separated active sites in a given solid is of prime importance to achieve high photocatalytic activity. Intense attention has been focused on the design and fabrication of single-site photocatalysts by using porous materials as a platform. Metal-organic frameworks (MOFs) have great potential in the design and fabrication of single-site photocatalysts due to their remarkable porosity, ultrahigh surface area, extraordinary tailorability, and significant diversity. MOFs can provide an abundant number of binding sites to anchor active sites, which results in a significant enhancement in photocatalytic performance. In this focus review, the development of single-site MOF photocatalysts that perform important and challenging chemical redox reactions, such as photocatalytic H2 production, photocatalytic CO2 conversion, and organic transformations, is summarized thoroughly. Successful strategies for the construction of single-site MOF photocatalysts are summarized and major challenges in their practical applications are noted.

Degradation paths of manganese-based MOF materials in a model oxidative environment: a computational study

Understanding MOF degradation for controlled drug delivery.

Catalytic combustion of diesel soot over Fe and Ag-doped manganese oxides: role of heteroatoms in the catalytic performances

Fe/Ag-doped manganese oxides show promising catalytic activities in diesel soot combustion, which occurviamechanisms involving activated surface/lattice oxygen species.

Enhanced catalytic activity of MnCo-MOF-74 for highly selective aerobic oxidation of substituted toluene

Novel MnCo-MOF-74 catalysts were prepared and used for highly selective aerobic oxidation of substituted toluene under mild conditions.

Photocatalytic production of hydrogen peroxide through selective two-electron reduction of dioxygen utilizing amine-functionalized MIL-125 deposited with nickel oxide nanoparticles

Photocatalytic H₂O₂ production via two-electron reduction of O₂ is realized by visible-light irradiation of a Ti-based metal–organic framework, MIL-125-NH₂.

Solvent-dependent variations of both structure and catalytic performance in three manganese coordination polymers

Three new Mn-based MOFs have been prepared, and a 3D framework can act as an efficient and recycled catalyst in CO₂ cycloaddition with different epoxides.