Engineering Heterogeneous Catalysis with Strong Metal–Support Interactions: Characterization,Theory and Manipulation

Strong metal–support interactions (SMSI) represent a classic yet fast-growing area in catalysis research. The SMSI phenomenon results in the encapsulation and stabilization of metal nanoparticles (NPs) with the support material that significantly impacts the catalytic performance through regulation of the interfacial interactions. Engineering SMSI provides a promising approach to steer catalytic performance in various chemical processes, which serves as an effective tool to tackle energy and environmental challenges. Our Minireview covers characterization, theory, catalytic activity, dependence on the catalytic structure and inducing environment of SMSI phenomena. By providing an overview and outlook on the cutting-edge techniques in this multidisciplinary research field, we not only want to provide insights into the further exploitation of SMSI in catalysis, but we also hope to inspire rational designs and characterization in the broad field of material science and physical chemistry.     

Controlled Annealing in Adaptive Multicomponent Gels

We use a pH-driven annealing process to convert between co-assembled and self-sorted networks in multicomponent gels. The initially formed gels at low pH are co-assembled, with the two components coexisting within the same self-assembled structures. We use an enzymatic approach to increase the pH, resulting in a gel-to-sol transition, followed by a hydrolysis to lower the pH once again. As the pH decreases, a self-sorted network is formed by a two-stage gelation process determined by the pK_a of each component. This approach can be expanded to layered systems to generate many varied systems by changing composition and rates of pH change, adapting their microstructure and so allowing access to a far greater range of morphologies and complexity than can be achieved in single component systems.     

Targeted Synthesis of Isomeric Naphthalene-Based 2D Kagome Covalent Organic Frameworks

Targeted synthesis of kagome ( kgm ) topologic 2D covalent organic frameworks remains challenging, presumably due to the severe dependence on building units and synthetic conditions. Herein, two isomeric “two-in-one” monomers with different lengths of substituted arms based on naphthalene core (p-Naph and m-Naph) are elaborately designed and utilized for the defined synthesis of isomeric kgm Naph-COFs. The two isomeric frameworks exhibit splendid crystallinity and showcase the same chemical composition and topologic structure with, however, different pore channels. Interestingly, C₆₀ is able to uniformly be encapsulated into the triangle channels of m-Naph-COF via in situ incorporation method, while not the isomeric p-Naph-COF, likely due to the different pore structures of the two isomeric COFs. The resulting stable C₆₀@m-Naph-COF composite exhibits much higher photoconductivity than the m-Naph-COF owing to charge transfer between the conjugated skeletons and C₆₀ guests.     

Enantioselective Synthesis of N−N Biaryl Atropisomers through Iridium(I)-Catalyzed C−H Alkylation with Acrylates

Enantioselective synthesis of N−N biaryl atropisomers is an emerging area but remains underexplored. The development of efficient synthesis of N−N biaryl atropisomers is in great demand. Herein, the construction of N−N biaryl atropisomers through iridium-catalyzed asymmetric C−H alkylation is reported for the first time. In the presence of readily available Ir precursor and Xyl-BINAP, a variety of axially chiral molecules based on indole-pyrrole skeleton were obtained in good yields (up to 98 %) with excellent enantioselectivity (up to 99 % ee). In addition, N−N bispyrrole atropisomers could also be synthesized in excellent yields and enantioselectivity. This method features perfect atom economy, wide substrate scope, and multifunctionalized products allowing diverse transformations.     

Transition Metal Catalysis in Living Cells: Progress,Challenges, and Novel Supramolecular Solutions

The importance of transition metal catalysis is exemplified by its wide range of applications, for example in the synthesis of chemicals, natural products, and pharmaceuticals. However, one relatively new application is for carrying out new-to-nature reactions inside living cells. The complex environment of a living cell is not welcoming to transition metal catalysts, as a diverse range of biological components have the potential to inhibit or deactivate the catalyst. Here we review the current progress in the field of transition metal catalysis, and evaluation of catalysis efficiency in living cells and under biological (relevant) conditions. Catalyst poisoning is a ubiquitous problem in this field, and we propose that future research into the development of physical and kinetic protection strategies may provide a route to improve the reactivity of catalysts in cells.     

Electron-Donors–Acceptors Interaction Enhancing Electrocatalytic Activity of Metal-Organic Polymers for Oxygen Reduction

Catalysts with metal-N_x sites have long been considered as effective electrocatalysts for oxygen reduction reaction (ORR), yet the accurate structure-property correlations of these active sites remain debatable. Report here is a proof-of-concept method to construct 1,4,8,11-tetraaza[14]annulene (TAA)-based polymer nanocomposites with well-managed electronic microenvironment via electron-donors/acceptors interaction of altering electron-withdrawing β-site substituents. DFT calculation proves the optimal −Cl substituted catalyst (CoTAA−Cl@GR) tailored the key OH* intermediate interaction with Co−N₄ sites under the d-orbital regulation, hence reaching the top of ORR performance with excellent turnover frequency (0.49 e s⁻¹ site⁻¹). The combination of in situ scanning electrochemical microscopy and variable-frequency square wave voltammetry techniques contribute the great ORR kinetics of CoTAA−Cl@GR to the relatively high accessible site density (7.71×10¹⁹ site g⁻¹) and fast electron outbound propagation mechanism. This work provides theoretical guidance for rational design of high-performance catalysts for ORR and beyond.     

Ruthenium-Catalyzed Activation of Nonpolar C−C Bonds via π-Coordination-Enabled Aromatization

Activation of C−C bonds allows editing of molecular skeletons, but methods for selective activation of nonpolar C−C bonds in the absence of a chelation effect or a driving force derived from opening of a strained ring are scarce. Herein, we report a method for ruthenium-catalyzed activation of nonpolar C−C bonds of pro-aromatic compounds by means of π-coordination-enabled aromatization. This method was effective for cleavage of C−C(alkyl) and C−C(aryl) bonds and for ring-opening of spirocyclic compounds, providing an array of benzene-ring-containing products. The isolation of a methyl ruthenium complex intermediate supports a mechanism involving ruthenium-mediated C−C bond cleavage.     

A Strategy for Controlling the Polymerizations of Thiyl Radical Propagation by RAFT Agents

The ability to extend the polymerizations of thiyl radical propagation to be regulated by existing controlled methods would be highly desirable, yet remained very challenging to achieve because the thiyl radicals still cannot be reversibly controlled by these methods. In this article, we reported a novel strategy that could enable the radical ring-opening polymerization of macrocyclic allylic sulfides, wherein propagating specie is thiyl radical, to be controlled by reversible addition–fragmentation chain transfer (RAFT) agents. The key to the success of this strategy is the propagating thiyl radical can undergo desulfurization with isocyanide and generate a stabilized alkyl radical for reversible control. Systematic optimization of the reaction conditions allowed good control over the polymerization, leading to the formation of polymers with well-defined architectures, exemplified by the radical block copolymerization of macrocyclic allylic sulfides and vinyl monomers and the incorporation of sequence-defined segments into the polymer backbone. This work represents a significant step toward directly enabling the polymerizations of heteroatom-centered radical propagation to be regulated by existing reversible-deactivation radical polymerization techniques.     

Visible-Light-Induced Control over Reversible Single-Chain Nanoparticle Folding

We introduce a class of single-chain nanoparticles (SCNPs) that respond to visible light (λ_max=415 nm) with complete unfolding from their compact structure into linear chain analogues. The initial folding is achieved by a simple esterification reaction of the polymer backbone constituted of acrylic acid and polyethylene glycol carrying monomer units, introducing bimane moieties, which allow for the photochemical unfolding, reversing the ester-bond formation. The compaction and the light driven unfolding proceed cleanly and are readily followed by size exclusion chromatography (SEC) and diffusion ordered NMR spectroscopy (DOSY), monitoring the change in the hydrodynamic radius (R_H). Importantly, the folding reaction and the light-induced unfolding are reversible, supported by the high conversion of the photo cleavage. As the unfolding reaction occurs in aqueous systems, the system holds promise for controlling the unfolding of SCNPs in biological environments.