Formation of C–C and C–Heteroatom Bonds by C–H Activation by Metal Organic Frameworks as Catalysts or Supports

Efficient base- and ligand-free palladium catalysed O-arylation of phenols in choline chloride:triethanolamine as a reusable deep eutectic solvent

In this paper, we present a novel and sustainable approach using choline chloride:triethanolamine as a green, efficient and reusable deep eutectic solvent (DES) for Pd-catalysed O-arylation reactions with Pd/BaSO4 (10%). By using the unique properties of DESs, we successfully achieved C-O bond formation without the need for additional solvents, bases and ligands. This solvent/catalyst system ([ChCl][TEA]2) functioned as a dual catalyst and solvent system, enabling fast and environmentally friendly C-O bond formation from phenol derivatives and electron-deficient aryl halides, leading to remarkable yields under mild reaction conditions. To identify and characterize this DES, we employed differential scanning calorimetry, thermogravimetric analysis, Fourier-transform infrared spectroscopy, refractive index, viscosity, the potential of hydrogen (pH) and conductivity measurements. One of the remarkable advantages of this DES system is its exceptional stability. This solvent/catalyst system exhibited high stability throughout the reaction cycles, showing no significant loss of activity. As a result, this DES and catalyst (Pd/BaSO4 (10%)) can be easily recycled and re-used for up to three consecutive cycles, making it an economically and environmentally attractive option for organic reactions. Our approach offers several key benefits, including simple catalyst preparation, quick reaction times and excellent production efficiency.

Stability of Zr-Based UiO-66 Metal-Organic Frameworks in Basic Solutions

Although Zr-based metal-organic frameworks (MOFs) exhibit robust chemical and physical stability in the presence of moisture and acidic conditions, their susceptibility to nucleophilic attacks from bases poses a critical challenge to their overall stability. Herein, we systematically investigate the stability of Zr-based UiO-66 (UiO = University of Oslo) MOFs in basic solutions. The impact of 11 standard bases, including inorganic salts and organic bases, on the stability of these MOFs is examined. The destruction of the framework is confirmed through powder X-ray diffraction (PXRD) patterns, and the monitored dissolution of ligands from the framework is assessed using nuclear magnetic resonance (NMR) spectroscopy. Our key findings reveal a direct correlation between the strength and concentration of the base and the destruction of the MOFs. The summarized data provide valuable insights that can guide the practical application of Zr-based UiO-66 MOFs under basic conditions, offering essential information for their optimal utilization in various settings.

Reaction mechanism - explored with the unified reaction valley approach

One of the ultimate goals of chemistry is to understand and manipulate chemical reactions, which implies the ability to monitor the reaction and its underlying mechanism at an atomic scale. In this article, we introduce the Unified Reaction Valley Approach (URVA) as a tool for elucidating reaction mechanisms, complementing existing computational procedures. URVA combines the concept of the potential energy surface with vibrational spectroscopy and describes a chemical reaction via the reaction path and the surrounding reaction valley traced out by the reacting species on the potential energy surface on their way from the entrance to the exit channel, where the products are located. The key feature of URVA is the focus on the curving of the reaction path. Moving along the reaction path, any electronic structure change of the reacting species is registered by a change in the normal vibrational modes spanning the reaction valley and their coupling with the path, which recovers the curvature of the reaction path. This leads to a unique curvature profile for each chemical reaction, with curvature minima reflecting minimal change and curvature maxima indicating the location of important chemical events such as bond breaking/formation, charge polarization and transfer, rehybridization, etc. A decomposition of the path curvature into internal coordinate components or other coordinates of relevance for the reaction under consideration, provides comprehensive insight into the origin of the chemical changes taking place. After giving an overview of current experimental and computational efforts to gain insight into the mechanism of a chemical reaction and presenting the theoretical background of URVA, we illustrate how URVA works for three diverse processes, (i) [1,3] hydrogen transfer reactions; (ii) α-keto-amino inhibitor for SARS-CoV-2 Mpro; (iii) Rh-catalyzed cyanation. We hope that this article will inspire our computational colleagues to add URVA to their repertoire and will serve as an incubator for new reaction mechanisms to be studied in collaboration with our experimental experts in the field.

Recyclable Magnetic Cu-MOF-74-Catalyzed C(sp2)-N Coupling and Cyclization under Microwave Irradiation: Synthesis of Imidazo[1,2-c]quinazolines and Their Analogues

Magnetic Cu-MOF-74 (Fe₃O₄@SiO₂@Cu-MOF-74) was synthesized for the first time by grafting MOF-74 (copper as the metal center) on the surface of core-shell magnetic carboxyl-functionalized silica gel (Fe₃O₄@SiO₂-COOH), which was prepared by coating core Fe₃O₄ nanoparticles with hydrolyzed 2-(3-(triethoxysilyl)propyl)succinic anhydride and tetraethyl orthosilicate. The structure of Fe₃O₄@SiO₂@Cu-MOF-74 nanoparticles was characterized by Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and transmission electron microscopy (TEM). The prepared Fe₃O₄@SiO₂@Cu-MOF-74 nanoparticles could be applied as a recyclable catalyst to the synthesis of N-fused hybrid scaffolds. 2-(2-Bromoaryl)imidazoles and 2-(2-bromovinyl)imidazoles were coupled and cyclized with cyanamide in DMF in the presence of a catalytic amount of Fe₃O₄@SiO₂@Cu-MOF-74 along with a base to give imidazo[1,2-c]quinazolines and imidazo[1,2-c]pyrimidines, respectively, in good yields. The Fe₃O₄@SiO₂@Cu-MOF-74 catalyst could be easily recovered by a super magnetic bar and recycled more than four times while almost maintaining catalytic activity.

Solubilizing Metal-Organic Frameworks for an In Situ IR-SEC Study of a CO2 Reduction Catalyst

Metal-organic frameworks (MOFs) are typically assembled by bridging metal centers with organic linkers for various applications, including providing robust support for heterogeneous catalysts for CO2 reduction. In this study, we have demonstrated the solubilization of a MOF tethered to a CO2-reducing electrocatalyst and studied its fundamental electrochemistry in THF solvent using infrared spectroelectrochemistry (IR-SEC). The fundamental electrochemical properties of this immobilized catalyst were compared to that of its homogeneous counterpart. This approach provides a foundation for future experimental studies to bridge the gap between homogeneous and heterogeneous electrocatalysis.

Metal-Organic Frameworks as Electrocatalysts

Transition metal complexes are well-known homogeneous electrocatalysts. In this regard, metal-organic frameworks (MOFs) can be considered as an ensemble of transition metal complexes ordered in a periodic arrangement. In addition, MOFs have several additional positive structural features that make them suitable for electrocatalysis, including large surface area, high porosity, and high content of accessible transition metal with exchangeable coordination positions. The present review describes the current state in the use of MOFs as electrocatalysts, both as host of electroactive guests and their direct electrocatalytic activity, particularly in the case of bimetallic MOFs. The field of MOF-derived materials is purposely not covered, focusing on the direct use of MOFs or its composites as electrocatalysts. Special attention has been paid to present strategies to overcome their poor electrical conductivity and limited stability.

Plasma Meets MOFs: Synthesis, Modifications, and Functionalities

As a porous and network materials consisting of metals and organic ligands, metal-organic frameworks (MOFs) have become one of excellent crystalline porous materials and play an important role in the era about materials science. Plasma, as a useful tool for stimulating efficient reactions under many conditions, and the plasma-assisted technology gets more attractions and endows MOFs more properties. Based on its feature, the research about the modifications and functionalities of MOFs have been developing a certain extent. This review contains a description of the methods for plasma-assisted modification and synthesis of MOFs, with specifically focusing on the plasma-assisted potential for modifications and functionalities of MOFs. The different applications of plasma-assisted MOFs were also presented.

Phosphomolybdic acid hydrate encapsulated in MIL-53 (Fe): a novel heterogeneous heteropoly acid catalyst for ultrasound-assisted regioselective nitration of phenols

In this study, a heterogeneous catalyst, PMA@MIL-53 (Fe) (MIL ⇒ Matériaux de l'Institut Lavoisier), has been used to replace the usual mineral acids such as sulfuric acid. A wide variety of nitration methods require the use of a mixture of acids such as concentrated nitric acid and sulfuric acid, which result in producing a large amount of acidic waste. During recent years, the use of the heterogeneous system for the nitration of aromatic compounds has been highly considered and used by chemists due to some specific advantages, i.e. easy separation of the product from the reaction mixture, the possibility of recycling and reusing the catalyst, etc. Herein, the catalyst was synthesized using a metal-organic framework and a heteropoly phosphomolybdic acid. The PMA@MIL-53 (Fe) was prepared using a similar method of MIL-53 (Fe) synthesis. Afterwards, FeCl3·6H2O and 1,4-benzene dicarboxylic acid (BDC) in a dimethylformamide solution were placed in an ultrasound bath and, then, HPA (heteropoly acid) was added to the reaction mixture. The PMA (phosphomolybdic acid) encapsulation in MIL-53 (Fe) was confirmed using various analysis. Under optimal conditions, the catalytic activity of PMA@MIL-53 (Fe) was evaluated in nitration of phenol under ultrasonic waves. Besides, the ratio of the two products of ortho and para was obtained using GC. Optimum conditions were reached after 15 minutes, in such a way that the loaded PMA was 0.02 g under optimal conditions, the efficiencies of ortho-nitrophenol and para nitrophenol were 54.98 and 45.01, respectively.

Cu-α-diimine Compounds Encapsulated in Porous Materials as Catalysts for Electrophilic Amination of Aromatic C-H Bonds

Electrophilic amination has emerged as a more environmentally benign approach to construct arene C-N bonds. However, heterogeneous catalysts remain largely unexplored in this area, even though their use could facilitate product purification and catalyst recovery. Here we investigate strategies to heterogenize a Cu(2,2'-bipyridine) catalyst for the amination of arenes lacking a directing group with hydroxylamine-O-sulfonic acid (HOSA). Besides immobilization of Cu on a metal-organic framework (MOF) or covalent organic framework (COF) with embedded 2,2'-bipyridines, a ship-in-a-bottle approach was followed in which the Cu complex is encapsulated in the pores of a zeolite. Recyclability and hot centrifugation tests show that zeolite Beta-entrapped Cu^II(2,2'-bipyridine) is superior in terms of stability. With N-methylmorpholine as a weakly coordinating, weak base, simple arenes, such as mesitylene, could be aminated with yields up to 59%, corresponding to a catalyst TON of 24. The zeolite could be used in three consecutive runs without a decrease in activity. Characterization of the catalyst by EPR and XAS showed that the active catalytic complex consisted of a site-isolated Cu^II species with one 2,2'-bipyridine ligand.

Simultaneous Generation of Methyl Esters and CO in Lignin Transformation

Lignin is an abundant renewable carbon source. Due to its complex structure, utilization of lignin is very challenging. Herein, we describe an efficient strategy for the simultaneous utilization of lignin, in which the methoxy groups in lignin react with carboxylic acids to generate methyl carboxylates and the other alkyl and phenyl carbons react with oxygen to predominantly form CO that can be used directly in carbonylation reactions. The method was applied to the methylation of various functionalized aryl and alkyl carboxylic acids, including natural compounds, to produce valuable chemicals, including pharmaceuticals. No solid or liquid residues remain after the reaction. Mechanistic studies demonstrate that a well-ordered C-C and C-O bond activation sequence takes place to realize total transformation of lignin. This work opens a way for transformation of the entire lignin polymer into valuable products, exemplified by the synthesis of the pharmaceutical, Ramipril, on a gram scale.

Supported Palladium Nanoparticles Catalyzed Intermolecular Carbopalladation of Nitriles and Organoboron Compounds

The first heterogeneous catalyzed example for the direct synthesis of aromatic ketones via intermolecular carbopalladation of aliphatic nitriles and organoboron compounds was developed. This mild method proceeds with a supported palladium nanoparticles catalyst that could be reused and recycled five times. The fresh and used catalysts were characterized by XPS and TEM. The XPS analysis indicated that Pd0 was the active species for the reaction. This methodology provides a mild and cost-effective strategy for the efficient synthesis of ketones.

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.

C–N coupling reactions with arenes through C–H activation: the state-of-the-art versus the principles of green chemistry

Herein, we discuss the state-of-the-art in arene C–N coupling through C–H activation and to what extent it complies with the principles of green chemistry, with a focus on heterogeneously catalysed systems.

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.

Hierarchical Porous MIL-101(Cr) Solid Acid-Catalyzed Production of Value-Added Acetals from Biomass-Derived Furfural

Considering economic and environmental impacts, catalytic biomass conversion to valuable compounds has attracted more and more attention. Of particular interest is furfural, a versatile biorefinery platform molecule used as a feedstock for the production of fuels and fine chemicals. In this study, the Cr-based metal-organic frameworks (MOFs) MIL-101 were modified by chlorosulfonic acid, and MIL-101 was changed into a hierarchical MOF structure with smaller particles and lower particle crystallinity by CTAB, which significantly improved the acidic sites of the MOFs. The original and modified MIL-101(Cr) catalysts were characterized by XRD, N₂ adsorption-desorption, SEM, TEM, and FT-IR. The effects of different catalysts, reaction temperature, catalyst amount, and alcohol type on the reaction were studied. Under the action of the MOFs catalyst, a new mild route for the condensation of furfural with various alkyl alcohols to the biofuel molecules (acetals) was proposed. The conversion route includes the conversion of furfural up to 91% yield of acetal could be obtained within 1 h solvent-free and in room-temperature reaction conditions. The sulfonic acid-functionalized MIL-101(Cr) is easy to recover and reuse, and can still maintain good catalytic activity after ten runs.

Mechanistic insights into the α-branched amine formation with pivalic acid assisted C-H bond activation catalysed by Cp*Rh complexes

Density functional theory computations revealed a pivalic acid assisted C-H bond activation mechanism for rhodium catalyzed formation of α-branched amines with C-C and C-N bond couplings. The reaction energies of the [Cp*RhCl₂]₂ dimer and silver cations indicate that the Cp*RhCl⁺ cation is the active catalyst. The essential role of pivalic acid is a co-catalyst for the activation of the ortho-C(sp²)-H bond in phenyl(pyrrolidin-1-yl)methanone, while the reaction of NaHCO₃ and HCl reduces the overall barrier of the catalytic cycle. In the presence of both pivalic acid and NaHCO₃ in the reaction, the C(sp²)-H bond is activated through a concerted metallation deprotonation process, and the C-C bond coupling is the rate-determining step with a total free energy barrier of 23.9 kcal mol^-1. Without pivalic acid and NaHCO₃, the C(sp²)-H bond can only be activated through a σ-bond metathesis process and the free energy barrier increases to 32.2 kcal mol^-1. We also investigated the mechanisms of a side reaction for β-branched amine formation and the reaction without styrene and found that their free energy barriers are 33.4 and 30.5 kcal mol^-1, respectively.

Copper-Loaded Layered Bismuth Subcarbonate-Efficient Multifunctional Heterogeneous Catalyst for Concerted C-S/C-N Heterocyclization

An efficient self-supported Cu(II)Bi(III) bimetallic catalyst with a layered structure was designed and developed. By careful characterization of the as-prepared material, the host structure was identified to exhibit a Sillen-type bismutite framework, with copper(II) ions being loaded as guests. The heterogeneous catalyst enabled C–N and C–S arylations under mild reaction conditions and with high chemoselectivities, thus furnishing valuable phenothiazines via heterocyclization with wide substrate tolerance. As corroborated by detailed catalytic studies, the cooperative, bifunctional catalyst, bearing Lewis acid sites along with copper(II) catalytic sites, facilitated an intriguing concerted C–N/C–S heterocyclization mechanism. The heterogeneous nature of the catalytic reactions was verified experimentally. Importantly, the catalyst was successfully recycled and reused multiple times, persevering its original structural order as well as its initial activity.

Three Polyoxovanadates-Based Organic-Inorganic Hybrids: Structural Variation, Bifunctional Electrocatalytic Activities, and Computational Studies

Three bimetallic organic-inorganic hybrids based on the [V₂O₆]^2- building unit, [Cu(pty)(V₂O₆)]·H₂O (1), [Cu(pty)(V₂O₆)] (2), [Cu(tpy)(V₂O₆)] (3), (pty = 4'-(4″-pyridyl)-2,2':6',2″-terpyridine, tpy = 2,2':6',2″-terpyridine), were synthesized via a one-pot method. Hybrid 1 has a 1D straight chain architecture with [V₂O₆]^2- clusters and Cu-pty complexes; hybrids 2 and 3 possess a 2D sheet structure including 10-membered rings assembled from four [Cu(pty)]²⁺ motifs and six [V₂O₆]^2- clusters in 2, and two [Cu(tpy)]²⁺ units and eight [V₂O₆]^2- clusters in 3. Noteworthy, hybrids 1-3 can be employed as bifunctional electrocatalysts for electroreduction of nitrite and electrooxidation of ascorbic acid. Additionally, theoretical calculations including the molecular electrostatic potential and the frontier molecular orbital were performed to estimate the electronic structure of hybrids 1-3. The natural bond orbital analysis was also calculated to interpret the electron charge distribution.

Metal Nanoparticles as Sustainable Tools for C-N Bond Formation via C-H Activation

The design of highly active metal nanoparticles to be employed as efficient heterogeneous catalysts is a key tool for the construction of complex organic molecules and the minimization of their environmental costs. The formation of novel C-N bonds via C-H activation is an effective atom-economical strategy to access high value materials in pharmaceuticals, polymers, and natural product production. In this contribution, the literature of the last ten years on the use of metal nanoparticles in the processes involving direct C-N bond formation will be discussed. Where possible, a discussion on the role and influence of the support used for the immobilization and/or the metal chosen is reported. Particular attention was given to the description of the experiments performed to elucidate the active mechanism.

Electrochemical activation of C-H by electron-deficient W2C nanocrystals for simultaneous alkoxylation and hydrogen evolution

The activation of C-H bonds is a central challenge in organic chemistry and usually a key step for the retro-synthesis of functional natural products due to the high chemical stability of C-H bonds. Electrochemical methods are a powerful alternative for C-H activation, but this approach usually requires high overpotential and homogeneous mediators. Here, we design electron-deficient W2C nanocrystal-based electrodes to boost the heterogeneous activation of C-H bonds under mild conditions via an additive-free, purely heterogeneous electrocatalytic strategy. The electron density of W2C nanocrystals is tuned by constructing Schottky heterojunctions with nitrogen-doped carbon support to facilitate the preadsorption and activation of benzylic C-H bonds of ethylbenzene on the W2C surface, enabling a high turnover frequency (18.8 h-1) at a comparably low work potential (2 V versus SCE). The pronounced electron deficiency of the W2C nanocatalysts substantially facilitates the direct deprotonation process to ensure electrode durability without self-oxidation. The efficient oxidation process also boosts the balancing hydrogen production from as-formed protons on the cathode by a factor of 10 compared to an inert reference electrode. The whole process meets the requirements of atomic economy and electric energy utilization in terms of sustainable chemical synthesis.

α,β-Enone Borylation by Bis(Pinacolato)Diboron Catalyzed by Cu3(BTC)2 Using Cesium Carbonate as a Base

Cu₃(BTC)₂ (BTC: 1,3,5-benzenetricarboxylate) as a heterogeneous catalyst in the presence of cesium carbonate as a base is reported for the borylation of α,β-conjugated enones by bis(pinacolato)diboron (B₂pin₂). According to the hot-filtration test, Cu₃(BTC)₂ is acting as a heterogeneous catalyst. Further, Cu₃(BTC)₂ exhibits a wide substrate scope and can be reused in consecutive runs, maintaining a crystal structure as evidenced by powder X-ray diffraction (XRD). A suitable mechanism is also proposed for this transformation using Cu₃(BTC)₂ as catalyst.

A Hierarchical-Structured Impeller with Engineered Pd Nanoparticles Catalyzing Suzuki Coupling Reactions for High-Purity Biphenyl

Suzuki cross-coupling reactions catalyzed by palladium are authoritative protocols in fine-chemical synthesis. Mass transfer and catalyst activity are both significant factors affecting the reaction efficiency in heterogeneous reactions. Although the holistic catalysts hold great promise in heterogeneous reactions due to the enhanced mass transport and convenient recycling, the unsatisfied catalytic activity has impeded further large-scale applications. In addition, another pronounced barrier is the product separation in the intricate system. Here, the catalytic production and separation of biphenyl (purity of 99.7%) were achieved by integrating the Suzuki cross-coupling reactions and the crystallization separation for the first time. A hierarchical-structured impeller with Pd nanoparticles (NPs) loaded on the Ni(OH)₂ nanosheets was prepared to catalyze the Suzuki reactions for bromobenzene, which exhibits a high turnover frequency (TOF) value of 25,976 h^-1 and a yield of 99.5%. The X-ray absorption fine structure (XAFS) analysis has unveiled that the electron transfer between the Pd NPs and Ni(OH)₂ accounts for the greatly enhanced catalytic activity. The findings inspire new insights toward rational engineering of highly efficient holistic catalysts for Suzuki reaction, and the innovative integrated technology offers an avenue for the separation and collection of products.

Metal-Organic Frameworks as Versatile Heterogeneous Solid Catalysts for Henry Reactions

Metal–organic frameworks (MOFs) have become one of the versatile solid materials used for a wide range of applications, such as gas storage, gas separation, proton conductivity, sensors and catalysis. Among these fields, one of the more well-studied areas is the use of MOFs as heterogeneous catalysts for a broad range of organic reactions. In the present review, the employment of MOFs as solid catalysts for the Henry reaction is discussed, and the available literature data from the last decade are grouped. The review is organized with a brief introduction of the importance of Henry reactions and structural properties of MOFs that are suitable for catalysis. The second part of the review discusses the use of MOFs as solid catalysts for the Henry reaction involving metal nodes as active sites, while the third section provides data utilizing basic sites (primary amine, secondary amine, amides and urea-donating sites). While commenting on the catalytic results in these two sections, the advantage of MOFs over other solid catalysts is compared in terms of activity by providing turnover number (TON) values and the structural stability of MOFs during the course of the reaction. The final section provides our views on further directions in this field.

Rhodium-Catalyzed Redox-Neutral Olefination of Aryldiazenes with Acrylate Esters via C-H Activation and Transfer Hydrogenation

Rh(III)-catalyzed redox-neutral C-H olefination of aryldiazenecarboxylates has been realized using arylate esters as the olefinating reagents. This reaction proceeds under mild and redox-neutral conditions, resulting in integration of C-H activation and transfer hydrogenation. The chemoselectivity complements that of previously reported rhodium-catalyzed coupling of the same substrates.

Rhodium(i)/bisoxazolinephosphine-catalyzed regio- and enantioselective amination of allylic carbonates: a computational study

DFT calculations were performed to investigate the rhodium(i)/bisoxazolinephosphine-catalyzed regio- and enantioselective amination of allylic carbonates.

Boosting free radical type photocatalysis over Pd/Fe-MOFs by coordination structure engineering

The development of novel heterogeneous photocatalytic systems, along with a deep understanding of the relationship between the catalytic center chemical environment and the catalytic performance, is of great significance.

C(sp3)-H Monoarylation of Methanol Enabled by a Bidentate Auxiliary

With the assistance of a practical directing group (COAQ), the first catalytic protocol for the palladium-catalyzed C(sp³)-H monoarylation of methanol has been developed, offering an invaluable synthesis means to establish extensive derivatives of crucial arylmethanol functional fragments. Furthermore, the gram-scale reaction, broad substrate scope, excellent functional group compatibility, and even the practical synthesis of medicines further demonstrate the usefulness of this strategy.

Heterogeneous Single-Site Catalysts for C-H Activation Reactions: Pd(II)-Loaded S,O-Functionalized Metal Oxide-Bisphosphonates

Heterogeneous single-site catalysts contain spatially isolated, well-defined active sites. This allows not only their easy recovery by solid-liquid separation but also the detailed active site design similar to homogeneous catalysts. Here, heterogeneous Pd(II) single-site catalysts were assembled, based on mesoporous metal oxide-bisphosphonate materials as supports. This new family of hybrid organic-inorganic materials with tunable porosity was further functionalized with thioether ligands containing S,O-binding sites that enhance the activity of Pd(II) for C-H activation reactions. The structures of the resulting Pd(II) single-site catalysts were carefully analyzed via solid-state NMR spectroscopy, via texture analysis by N₂ physisorption, infrared spectroscopy, and transmission electron microscopy. Furthermore, the immediate environment of the isolated Pd(II) active sites was studied with X-ray absorption spectroscopy. A clear relationship between the thioether ligand surface density and catalyst activity could be established. Significantly higher yields were obtained using highly porous metal oxide-bisphosphonate materials as supports compared to materials with lower porosities, such as conventional metal oxides, indicating that the high surface area facilitates the presence of isolated, well-accessible S,O-supported Pd(II) active sites. A wide scope of model substrates, including industrially relevant arenes, can be converted with high yields by the optimal heterogeneous Pd catalyst.

Synthesis of 1,2-dihydro-1,3,5-triazine derivatives via Cu(II)-catalyzed C(sp3)-H activation of N,N-dimethylethanolamine with amidines

1,2-Dihydro-1,3,5-triazines and symmetrical 1,3,5-triazines were obtained in up to 81% yields from amidines and N,N-dimethylethanolamine catalyzed by CuCl2. The reaction involves three C-N bond formations during the oxidative annulation process and the mechanism was proposed. This efficient synthesis of 1,2-dihydro-1,3,5-triazines was developed for the first time.