Enhancing Heterogeneous Catalysis through Cooperative Hybrid Organic–Inorganic Interfaces

Emerging trends in the development and applications of triazine-based covalent organic polymers: a comprehensive review

Owing to unique structural features, triazine-based covalent organic polymers (COPs) have attracted significant attention and emerged as novel catalysts or support materials for an array of applications. Typically formed by reacting triazine-based monomers or the in situ creation of triazine rings from nitrile monomers, these COPs possess 2D/3D meso/microporous structures held together via strong covalent linkages. The quest for efficient, stable and recyclable catalytic systems globally necessitates the need for a well-structured and comprehensive review summarizing the synthetic methodologies and applications of triazine-based COPs. This review explores the various synthetic routes and applications of these COPs in photocatalysis, heterogeneous catalysis, electrocatalysis, adsorption and sensing. By exploring the latest advancements and future directions, this review offers valuable insights into the synthesis and applications of triazine-based COPs.

Induced chirality at the surface: fixation of a dynamic M/P invertible helical Co3 complex on SiO2

Dynamic M/P invertible helicity was successfully induced at a SiO2 surface immobilized with a dynamic helical trinuclear cobalt complex, [LCo3(NHMe2)6](OTf)3, using chiral ((R) or (S))-1-phenylethylamine. Solid-state CD spectra and theoretical calculations suggested that the fixation of the M/P helical complex on the surface via coordination interactions was the key factor of the induced chirality at the surface.

Novel lignin-supported copper complex as a highly efficient and recyclable nanocatalyst for Ullmann reaction

In this work, we prepared polyhydroxylated lignin by demethylation and hydroxylation of lignin, and grafted phosphorus-containing groups by nucleophilic substitution reaction, the resulting material could be used as a carrier for the preparation of heterogeneous Cu-based catalysts (PHL-CuI-OPR₂). The optimal PHL-CuI-OP^tBu₂ catalyst was characterized by FT-IR, TGA, BET, XRD, SEM-EDS, ICP-OES, XPS. The catalytic performance of PHL-CuI-OP^tBu₂ in the Ullmann CN coupling reaction was evaluated using iodobenzene and nitroindole as model substrates under nitrogen atmosphere with DME and H₂O as cosolvent at 95 °C for 24 h. The applicability of modified lignin-supported copper catalyst was investigated of various aryl/heteroaryl halides with indoles under optimal conditions, the corresponding products were obtained with high yield. Additionally, it could be easily recovered from the reaction medium by an easy centrifugation and washing.

Recent Advances in Copper-Based Solid Heterogeneous Catalysts for Azide-Alkyne Cycloaddition Reactions

The copper(I)-catalyzed azide−alkyne cycloaddition (CuAAC) reaction is considered to be the most representative ligation process within the context of the “click chemistry” concept. This CuAAC reaction, which yields compounds containing a 1,2,3-triazole core, has become relevant in the construction of biologically complex systems, bioconjugation strategies, and supramolecular and material sciences. Although many CuAAC reactions are performed under homogenous conditions, heterogenous copper-based catalytic systems are gaining exponential interest, relying on the easy removal, recovery, and reusability of catalytically copper species. The present review covers the most recently developed copper-containing heterogenous solid catalytic systems that use solid inorganic/organic hybrid supports, and which have been used in promoting CuAAC reactions. Due to the demand for 1,2,3-triazoles as non-classical bioisosteres and as framework-based drugs, the CuAAC reaction promoted by solid heterogenous catalysts has greatly improved the recovery and removal of copper species, usually by simple filtration. In so doing, the solving of the toxicity issue regarding copper particles in compounds of biological interest has been achieved. This protocol is also expected to produce a practical chemical process for accessing such compounds on an industrial scale.

Advances in Graphene/Inorganic Nanoparticle Composites for Catalytic Applications

Graphene-based nanocomposites with inorganic (metal and metal oxide) nanoparticles leads to materials with high catalytic activity for a variety of chemical transformations. Graphene and its derivatives such as graphene oxide, highly reduced graphene oxide, or nitrogen-doped graphene are excellent support materials due to their high surface area, their extended π-system, and variable functionalities for effective chemical interactions to fabricate nanocomposites. The ability to fine-tune the surface composition for desired functionalities enhances the versatility of graphene-based nanocomposites in catalysis. This review summarizes the preparation of graphene/inorganic NPs based nanocomposites and their use in catalytic applications. We discuss the large-scale synthesis of graphene-based nanomaterials. We have also highlighted the interfacial electronic communication between graphene/inorganic nanoparticles and other factors resulting in increased catalytic efficiencies.

Reusable Manganese Catalyst for Site-Selective Pyridine C-H Arylations and Alkylations

Herein, we disclose a recyclable, hybrid manganese catalyst for site‐selective azine C−H activation by weak amide assistance. The novel, reusable catalyst enabled C3–H arylation and C3–H alkylation with ample scope, and was characterized by detailed transmission electron microscopy analysis.

Metal Nanoparticles Immobilized on Molecularly Modified Surfaces: Versatile Catalytic Systems for Controlled Hydrogenation and Hydrogenolysis

The synthesis and use of supported metal nanoparticle catalysts have a long-standing tradition in catalysis, typically associated with the field of heterogeneous catalysis. More recently, the development and understanding of catalytic systems composed of metal nanoparticles (NPs) that are synthesized from organometallic precursors on molecularly modified surfaces (MMSs) have opened a conceptually new approach to the design of multifunctional catalysts (NPs@MMS). These complex yet fascinating materials bridge molecular ("homogeneous") and material ("heterogeneous") approaches to catalysis and provide access to catalytic systems with tailor-made reactivity through judicious combinations of supports, molecular modifiers, and nanoparticle precursors. A particularly promising field of application is the controlled activation and transfer of dihydrogen, enabling highly selective hydrogenation and hydrogenolysis reactions as relevant for the conversion of biogenic feedstocks and platform chemicals as well as for novel synthetic pathways to fine chemicals and even pharmaceuticals. Consequently, the topic offers an emerging field for interdisciplinary research activities involving organometallic chemists, material scientists, synthetic organic chemists, and catalysis experts.This Account will provide a brief overview of the historical background and cover examples from the most recent developments in the field. A coherent account on the methodological and experimental basis will be given from the long-standing experience in our laboratories. MMSs are widely accessible via chemisorption and physisorption methods for the generation of stable molecular environments on solid surfaces, whereby a special emphasis is given here to ionic liquid-type molecules as modifiers (supported ionic liquid phases, SILPs) and silica as support material. Metal nanoparticles are synthesized following an organometallic approach, allowing the controlled formation of small and uniformly dispersed monometallic or multimetallic NPs in defined composition. A combination of techniques from molecular and material characterization provides a detailed insight into the structure of the resulting materials across various scales (electron microscopy, solid-state NMR, XPS, XAS, etc.).The molecular functionalities grafted on the silica surface have a pronounced influence on the formation, stabilization, and reactivity of the NPs. The complementary and synergistic fine-tuning of the metal and its molecular environment in NPs@MMSs allow in particular the control of the activation of hydrogen and its transfer to substrates. Monometallic (Ru, Rh, Pd) monofunctional NPs@MMSs possess excellent activities for the hydrogenation of alkenes, alkynes, and arenes for which a nonpolarized (homolytic) activation of H2 is predominant. The incorporation of 3d metals in noble metal NPs to give bimetallic (FeRu, CoRh, etc.) monofunctional NPs@MMSs favors a more polarized H2 activation and thus its transfer to the C═O bond, while at the same time preventing the arrangement of noble metal atoms necessary for ring hydrogenation. The incorporation of reactive functionalities, such as, for example, a -SO3H moiety on NPs@MMSs, results in bifunctional catalysts enabling the heterolytic cleavage corresponding to a formal H-/H+ transfer. Consequently, such catalysts possess excellent deoxygenation activity with strong synergistic effects arising from an intimate contact between the nanoparticles and the molecular functionality.While many more efforts are still required to explore, control, and understand the chemistry of NPs@MMS catalysts fully, the currently available examples already highlight the large potential of this approach for the rational design of multifunctional catalytic systems.

Surface and Interface Engineering: Molybdenum Carbide-Based Nanomaterials for Electrochemical Energy Conversion

Molybdenum carbide (Mo_x C)-based nanomaterials have shown competitive performances for energy conversion applications based on their unique physicochemical properties. A large surface area and proper surface atomic configuration are essential to explore potentiality of Mo_x C in electrochemical applications. Although considerable efforts are made on the development of advanced Mo_x C-based catalysts for energy conversion with high efficiency and stability, some urgent issues, such as low electronic conductivity, low catalytic efficiency, and structural instability, have to be resolved in accordance with their application environments. Surface and interface engineering have shown bright prospects to construct highly efficient Mo_x C-based electrocatalysts for energy conversion including the hydrogen evolution reaction, oxygen evolution reaction, nitrogen reduction reaction, and carbon dioxide reduction reaction. In this Review, the recent progresses in terms of surface and interface engineering of Mo_x C-based electrocatalytic materials are summarized, including the increased number of active sites by decreasing the particle size or introducing porous or hierarchical structures and surface modification by introducing heteroatom(s), defects, carbon materials, and others electronic conductive species. Finally, the challenges and prospects for energy conversion on Mo_x C-based nanomaterials are discussed in terms of key performance parameters for the catalytic performance.

Recyclable Ruthenium Catalyst for Distal meta-C-H Activation

We disclose the unprecedented hybrid-ruthenium catalysis for distal meta-C-H activation. The hybrid-ruthenium catalyst was recyclable, as was proven by various heterogeneity tests, and fully characterized with various microscopic and spectroscopic techniques, highlighting the physical and chemical stability. Thereby, the hybrid-ruthenium catalysis proved broadly applicable for meta-C-H alkylations of among others purine-based nucleosides and natural product conjugates. Additionally, its versatility was further reflected by meta-C-H activations through visible-light irradiation, as well as para-selective C-H activations.

On the Importance of Silane Infusion Order on the Microscopic and Macroscopic Properties of Multifunctional Charge Gradients

Four multicomponent charge gradients containing acidic and basic functionalities were prepared via sol-gel processes and the controlled-rate infusion (CRI) method to more clearly understand how preparation conditions influence macroscopic properties. CRI is used to form gradients by infusing reactive alkoxysilanes into a glass vial housing a vertically oriented modified silicon wafer. The concentration and time of infusion of the silane solutions were kept constant. Only the sequence of infusion of the silane solutions was changed. The first set of samples was prepared by initially infusing a solution containing 3-aminopropyltriethoxysilane (APTES) followed by a mercaptopropyltrimethoxysilane (MPTMS) solution. The individual gradients were formed either in an aligned or opposed fashion with respect to the initial gradient. The second set of samples was prepared by infusing the MPTMS solution first followed by the APTES solution, again in either an aligned or opposed fashion. To create charge gradients (NH3 +, SO3 -), the samples were immersed into H2O2. The extent of modification, the degree of protonation of the amine, and the thicknesses of the individual layers were examined by X-ray photoelectron spectroscopy (XPS) and spectroscopic ellipsometry. The wettability of the individual gradients was assessed via static contact angle measurements. The results demonstrate the importance of infusion order and how it influences the macroscopic and microscopic properties of gradient surfaces including the surface concentration, packing density, degree of protonation, and ultimately wettability. When the gradient materials are prepared via infusion of the APTES sol first, it results in increased deposition of both the amine and thiol groups as evidenced by XPS. Interestingly, the total thickness evaluated from ellipsometry was independent of the infusion order for the aligned gradients, indicative of significant differences in the film density. For the opposed gradients, however, the infusion of APTES first leads to a significantly thicker composite film. Furthermore, it also leads to a more pronounced gradient in the protonation of the amine, which introduces a very different surface wettability. The use of aminosilanes provides a viable approach to create gradient surfaces with different functional group distributions. These studies demonstrate that the controlled placement of functional groups on a surface can provide a new route to prepare gradient materials with improved performance.

Porous Organic Frameworks Featured by Distinct Confining Fields for the Selective Hydrogenation of Biomass-Derived Ketones

The asymmetric hydrogenation of biomass-derived molecules for the preparation of single enantiomer compounds is an effective method to reduce the rapid consumption of fossil resources. Porous organic frameworks (POFs) with pure organic surfaces may provide unusual confinement effects for organic substrates in chiral catalysis. Here, a series of POF catalysts are designed with chiral active centers decorated into sharply defined one-dimensional channels with diameters in the range of 1.2-2.9 nm. Due to the synergistic effect originating from the conjugated inner wall, the POF material (aperture size 2.4 nm) concentrates over 90% of aromatic species into the porous architecture, and its affinity is one or two orders of magnitude higher than those of classical porous solids. As determined by PBE+D3 calculation, the phenyl fragment reveals strong π-π interaction for steric hindrance around the metal active site to achieve stronger asymmetric induction. Therefore, this POF catalyst achieves high conversion (>99% yield) and enantioselectivity (>99% ee) for various substrates. The advantages of using the POF platform as a chiral catalyst can provide new perspectives on POF-based solid-state host-guest chemistry and asymmetric heterogeneous catalysis.

Photoinduced Heterogeneous C-H Arylation by a Reusable Hybrid Copper Catalyst

Heterogeneous copper catalysis enabled photoinduced C-H arylations under exceedingly mild conditions at room temperature. The versatile hybrid copper catalyst provided step-economical access to arylated heteroarenes, terpenes and alkaloid natural products with various aryl halides. The hybrid copper catalyst could be reused without significant loss of catalytic efficacy. Detailed studies in terms of TEM, HRTEM and XPS analysis of the hybrid copper catalyst, among others, supported its outstanding stability and reusability.

Heterogeneous Synergistic Catalysis for Promoting Aza-Michael–Henry Tandem Reaction for the Synthesis of Chiral 3-Nitro-1,2-Dihydroquinoline

Heterogeneous synergistic catalysis by SBA-15 immobilized chiral amines catalysts has promoted efficient aza-Michael–Henry tandem reaction for the synthesis of chiral 3-Nitro-1,2-Dihydroquinoline. Final products in the asymmetric aza-Michael–Henry cascade reactions between 2-aminobenzaldehyde and β-nitrostyrolene were afforded in a yield of 85% and an enantiomeric excess (ee) value of 98% on (S)-(–)-2-aminomethyl-1-ethylpyrrolidine immobilized SBA-15. SBA-15-AEP catalyst has been also extended to the asymmetric aza-Michael–Henry cascade reaction of substituted R1-2-aminobenzaldehyde and R2-substituted nitroolefin. The heterogeneous synergistic mechanism for both tertiary amine and secondary amine immobilized mesoporous has been proposed in detail including the geometrical constraints in the ee promotion.

Synthesis of discrete catalytic oligomers and their potential in silica-supported cooperative catalysis

The synthesis of discrete catalytic oligomers and their potential in supported cooperative catalysis are presented.

Organic-Inorganic Hybrid Materials: Multi-Functional Solids for Multi-Step Reaction Processes

The design of new hybrid materials with tailored properties at the nano-, meso-, and macro-scale, with the use of structural functional nanobuilding units, is carried out to obtain specific multi-functional materials. Organization into controlled 1D, 2D, and 3D architectures with selected functionalities is key for developing advanced catalysts, but this is hardly accomplished using conventional synthesis procedures. The use of pre-formed nanostructures, derived either from known materials or made with specific innovative synthetic methodologies, has enormous potential in the generation of multi-site catalytic materials for one-pot processes. The present concept article introduces a new archetype wherein self-assembled nanostructured builder units are the base for the design of multifunctional catalysts, which combine catalytic efficiency with fast reactant and product diffusion. The article addresses a new generation of versatile hybrid organic-inorganic multi-site catalytic materials for their use in the production of (chiral) high-added-value products within the scope of chemicals and fine chemicals production. The use of those multi-reactive solids for more nanotechnological applications, such as sensors, due to the inclusion of electron donor-acceptor structural arrays is also considered, together with the adsorption-desorption capacities due to the combination of hydrophobic and hydrophilic sub-domains. The innovative structured hybrid materials for multipurpose processes here considered, can allow the development of multi-stage one-pot reactions with industrial applications, using the materials as one nanoreactor systems, favoring more sustainable production pathways with economic, environmental and energetic advantages.

Chiral catalysts immobilized on achiral polymers: effect of the polymer support on the performance of the catalyst

Achiral polymeric supports can have important positive effects on the activity, stability and selectivity of supported chiral catalysts.

Acid–base bifunctional amphiphilic organic nanotubes as a catalyst for one-pot cascade reactions in water

A novel acid–base bifunctional amphiphilic organic nanotube is synthesized and used for one-pot deacetalization-Knoevenagel cascade reactions in water.

Molecular catalysis at polarized interfaces created by ferroelectric BaTiO3

Colloidal suspensions of ferroelectric BaTiO₃ nanoparticles act as a dispersible polarized interface that can influence the selectivity of non-faradaic reactions.

The local environment at polarized solid–liquid interfaces provides a unique medium for chemical reactions that could be exploited to control the selectivity of non-faradaic reactions. Polarized interfaces are commonly prepared by applying a voltage to an electrode in an electrolyte solution, but it is challenging to achieve high surface charge densities while suppressing faradaic reactions. Ferroelectric materials have permanent surface charge densities that arise from the dipole moments of ferroelectric domains and can be used to create polarized solid–liquid interfaces without applying a voltage. We studied the effects of ferroelectric oxides on the selectivity of a Rh porphyrin-catalyzed carbene rearrangement. The addition of ferroelectric BaTiO₃ nanoparticles to the reaction solution changed the product ratio in the same direction and by a similar magnitude as performing the reaction at an electrode–electrolyte interface polarized by a voltage. The results demonstrate that colloidal suspensions of BaTiO₃ nanoparticles act as a dispersible polarized interface that can influence the selectivity of non-faradaic reactions.

Heterogeneous enantioselective synthesis of chromans via the oxa-Michael–Michael cascade reaction synergically catalyzed by grafted chiral bases and inherent hydroxyls on mesoporous silica surface

A heterogeneous enantioselective oxa-Michael–Michael reaction for the synthesis of chromans has been developed on bifunctional catalysts, resulting in excellent catalytic performance.

Preparation and catalytic performance of a molecularly imprinted Pd complex catalyst for Suzuki cross-coupling reactions

A molecularly imprinted Pd complex catalyst was successfully designed and prepared on a SiO₂ surface for shape-selective Suzuki cross-coupling reaction.

Probing Heterogeneity and Bonding at Silica Surfaces through Single-Molecule Investigation of Base-Mediated Linkage Failure

The nature of silica surfaces is relevant to many chemical systems, including heterogeneous catalysis and chromatographies utilizing functionalized-silica stationary phases. Surface linkages must be robust to achieve wide and reliable applicability. However, silyl ether-silica support linkages are known to be susceptible to detachment when exposed to basic conditions. We use single-molecule spectroscopy to examine the rate of surface linkage failure upon exposure to base at a variety of deposition conditions. Kinetic analysis elucidates the role of thermal annealing and addition of blocking layers in increasing stability. Critically, it was found that successful surface modification strategies alter the rate at which base molecules approach the silica surface as opposed to reducing surface linkage reactivity. Our results also demonstrate that the innate structural diversity of the silica surface is likely the cause of observed heterogeneity in surface-linkage disruption kinetics.