Catalytic Organic Transformations Research Articles

Development of Catalytic Organic Transformations Using Carbon Dioxide toward Environmentally-Friendly Process

Development of Catalytic Organic Transformations Using Carbon Dioxide toward Environmentally-Friendly Process

The resurgence of old material: The impact of boehmite-derived catalytic material on the formation of dihydropyran compounds and its application to access fragrant derivatives

Bulk materials are the oldest in heterogeneous catalysis, but with the resurgence of recent interest, it has emerged as one of the best catalytic tools to unlock their full potential. Boehmite-derived alumina materials are widely studied for catalytic organic transformations. Despite the progress, understanding the mechanistic insights of its catalytic behaviour has remained obscure. Here, we demonstrate the catalytic performance of a boehmite-derived alumina material to a highly selective catalytic process for the preparation of dihydropyran compounds. The catalytic material displayed excellent activity in terms of conversion (up to 99%) and selectivity (up to 99%). The material was characterized using different techniques and observed that the γ-alumina phase with inherent mild acidic character are key feature for the catalytic activity. Based on NMR and in situ FT-IR spectroscopic investigations a probable mechanism is proposed. This study expands the application of robust material for the preparation of industrially important fragrance compounds. The scope of the catalytic study encompasses a range of substrates and scale-up activities.

2,4,6‐Trimethylpyridine‐Derived Vinylene‐Linked Covalent Organic Frameworks for Confined Catalytic Esterification

AbstractKnoevenagel condensation is a powerful tool for the construction of vinylene‐linked covalent organic frameworks. Herein, we established a concise approach to vinylene‐linked COFs by Knoevenagel condensation at the multi‐methyl groups of a pyridine ring through in situ formation of an N‐acyl pyridinium cation in the presence of various acylating reagents. Following this strategy, two vinylene‐linked COFs were constructed using 2,4,6‐trimethylpyridine and multi‐aldehyde‐substituted aromatic derivatives as monomers. The resultant COFs are highly crystalline and assembled into hexagonal lattices with specific surface areas as large as 1915 m2 g−1 (vs. 1972 m2 g−1 of the theoretical value). The stable and abundant pyridine‐decorated regular nanochannels within the COFs allow for catalyzing the esterification of several pharmaceutical intermediates with distinct spatially confined selectivity and recyclability, representing an environmentally friendly catalytic organic transformation.

2,4,6-Trimethylpyridine-Derived Vinylene-Linked Covalent Organic Frameworks for Confined Catalytic Esterification.

Knoevenagel condensation is a powerful tool for the construction of vinylene-linked covalent organic frameworks. Herein, we established a concise approach to vinylene-linked COFs by Knoevenagel condensation at the multi-methyl groups of a pyridine ring through in situ formation of an N-acyl pyridinium cation in the presence of various acylating reagents. Following this strategy, two vinylene-linked COFs were constructed using 2,4,6-trimethylpyridine and multi-aldehyde-substituted aromatic derivatives as monomers. The resultant COFs are highly crystalline and assembled into hexagonal lattices with specific surface areas as large as 1915 m2 g-1 (vs. 1972 m2 g-1 of the theoretical value). The stable and abundant pyridine-decorated regular nanochannels within the COFs allow for catalyzing the esterification of several pharmaceutical intermediates with distinct spatially confined selectivity and recyclability, representing an environmentally friendly catalytic organic transformation.

Noble metal nanoparticles dispersed on nanocellulose: a green platform for catalytic organic transformations

In recent years, plant-derived biomaterials, typically cellulose, acting as catalytic supports have a great impact on heterogeneous catalysis thanks to their biodegradability, non-toxicity, low-cost, availability and easy-implementation. As the most abundant biopolymer found in nature, cellulose consists of repeating cellobiose units which are built up from two anhydroglucose rings and linked by a β-1,4 glycosidic bond. The term of “nanocellulose” has been widely used to describe cellulose nano-objects, involving cellulose nanocrystals (CNCs), cellulose nanofibrils (CNFs) and bacterial cellulose (BC). Nanocellulose features high specific surface area and controllable surface chemistry, high crystalline structure, superior mechanical strength and thermal stability, resulting in its applications in food, cosmetics, pharmaceutical, biomedical and paper industries. Concerning to catalytic support application, the nanocellulose surface possesses the hydroxyl (in nature) or the sulfate ester groups (modified via acid hydrolysis), facilitating metal ions reduction towards the corresponding metal nanoparticles. In addition, the supramolecular structure of cellulose permits to disperse metal nanoparticles and prevent their agglomerations. In this context, nanocellulose is introduced as matrices for immobilizing noble metal nanoparticles and then applied to catalytic organic transformations.

Pyridine‐functionalized N‐heterocyclic carbene gold(I) binuclear complexes as molecular electrocatalysts for oxygen evolution reactions

N‐heterocyclic carbene (NHC) complexes of gold(I/III) attained immense interest in catalytic organic transformations and as anticancer agents against several types of human cancers; however, their potential as electrocatalysts is scarce. The electrocatalytic oxygen evolution reaction was performed for the first time using pyridine‐functionalized NHC gold(I) binuclear metallacycles (8 and 9) possessing aptly designed ligand field. Complexes were prepared by the transmetallation of corresponding silver(I) NHC complexes, which were prepared by in situ deprotonation of pyridine and aryl substituted 1,2,4‐triazolium hexafluorophosphate salts (6 and 7) with Ag2O under dark. Both triazolium salts and binuclear gold(I) metallacycles were thoroughly characterised by NMR and ATR‐IR spectral and elemental analyses. A bromide salt 4 and a binuclear gold complex 9 were elucidated for structure by single crystal X‐ray diffraction analysis. Complex 9 possesses distorted linear coordination geometry around the gold atoms by the coordination of carbene carbon and pyridine nitrogen atoms bearing close Au–Au interaction (3.251 Å). The binuclear gold complexes 8 and 9 (along with 10 wt% conductive mesoporous carbon) were investigated as molecular electrocatalysts in oxygen evolution reaction (OER), which evidenced an oxygen evolution overpotential of 2.422 and 2.370 V versus reversible hydrogen electrode (RHE), respectively, to attain a current density of 10 mA.cm−2. The Tafel slope values of 40.9 and 30.4 mV dec−1 for 8 and 9, respectively, indicate the reaction mechanism involved and the suitability of these complexes as apt electrocatalysts for OER. The stability of the prepared molecular electrocatalysts was investigated by cyclic voltammetry and chronoamperometry techniques.

Heterometal modified Fe3O4 hollow nanospheres as efficient catalysts for organic transformations

Iron oxides (e.g. Fe3O4) are ideal support materials for catalytic organic transformations owing to their sufficient natural abundance, excellent thermal stability and magnetic recycling property. Herein, we report the synthesis of active heterometal (M = Pd, Cu) modified Fe3O4 (M-Fe3O4) hollow nanospheres via a two-step solvothermal/annealing method. Due to the uniformly dispersed active heterometal species in the spherical shell of Fe3O4 hollow nanospheres, the as-prepared Pd-Fe3O4 catalyst exhibits remarkable catalytic activity toward 4-nitrophenol reduction with a turnover frequency of 145 min−1, and shows excellent stability and magnetic recyclability. The catalytic efficiency surpasses most of the similar Fe3O4 supported metal catalysts reported in literatures. Particularly, Cu-Fe3O4 exhibited 5 times higher activity for benzyl alcohol oxidation compared to that of bare Fe3O4 synthesized by the same procedure. An impressive conversion of 49.66% and an outstanding selectivity of 100% can be achieved. Moreover, the positive effects of Pd or Cu elements on the 4-NP molecule adsorption were further confirmed via both experimental results and theoretical studies. Our work demonstrate that the activity boost of iron oxides by heterometal modification is a promising strategy for performance improvement.

Electrospinning NH2-MIL-101/PAN nanofiber mats: A promising catalyst with Lewis acidic and basic bifunctional sites for organic transformation reactions

Because of their distinctive characteristics, like great surface area and capability of structure modifications, Metal-organic frameworks (MOFs) were endorsed as outstanding candidates for catalysis purposes. The incorporation of MOF into an organic polymer frameworks is thought to be a promising approach to enhance the catalysts performance, however, a facile and low-cost approach to prepare such catalysts is currently missing. Herein, a direct approach for integration the MOF into nanofibers with improved catalytic organic transformation reactions without film rupture is reported. The electrospun NH2-MIL-101 @polyacrylonitrile (PAN) catalyst nanofibers with varied MOF to PAN mass ratio was fabricated by a facile electrospinning approach and used as integrated catalyst for Friedel–Crafts acylation of anisole, esterification of amyl alcohol, and Knoveonagel condensation reaction of aldehydes. The fabricated MOF-catalysts nanofibers NH2-MIL-101 @PAN show effective anisole acylation, ester production, and Knoveonagel condensation reaction. The anisole acylation, ester production, and Knoveonagel condensation efficiency boosted to 90%, 79%, and 98% after incorporating NH2-MIL-101 nanocrystals into the elctrospun PAN nanofibers. The great surface area, available active centers in the pore architecture, and unsaturated Cr3+ Lewis acid centers are responsible for this exceptional performance. Because of its adaptability, our approach offers a cutting-edge and intriguing platform for the future tailoring of MOF fabrics with a wide range of practical uses.

Z-Scheme In2 S3 /NU-1000 Heterojunction for Boosting Photo-Oxidation of Sulfide into Sulfoxide under Ambient Conditions.

Photocatalytic oxidation of sulfide into sulfoxide has attracted extensive attention as an environmentally friendly strategy for chemical transformations or toxic chemicals degradation. Herein, we construct a series of In2 S3 /NU-1000 heterojunction photocatalysts, which can efficiently catalyze the oxidation of sulfides to form sulfoxides as the sole product under LED lamp (full-spectrum) illumination in air at room temperature. Especially, the sulfur mustard simulant, 2-chloroethyl ethyl sulfide (CEES), can also be photocatalytically oxidized with In2 S3 /NU-1000 to afford nontoxic 2-chloroethyl ethyl sulfoxide (CEESO) selectively and effectively. In contrast, individual NU-1000 and In2 S3 show very low catalytic activity on this reaction. The significantly improved photocatalytic activity is ascribed to the constructing of an efficient Z-scheme photocatalysts In2 S3 /NU-1000, which exhibits the enhancement of light harvesting, the promotion of photogenerated electron-hole separation, and the retention of high porosity of the parent MOF. Moreover, mechanism studies in photocatalytic oxidation reveal that the superoxide radical (. O2 - ) and singlet oxygen (1 O2 ) are the main oxidative species in the oxidation system. This work exploits the opportunities for the construction of porous Z-scheme photocatalysts based on the photoactive MOFs materials and inorganic semiconductors for promoting catalytic organic transformations. More importantly, it provides a route to the rational design of efficient photocatalysts for the detoxification of mustard gas.

Solvent-free autocatalytic supramolecular polymerization.

Solvent-free chemical manufacturing is one of the awaited technologies for addressing an emergent issue of environmental pollution. Here, we report solvent-free autocatalytic supramolecular polymerization (SF-ASP), which provides an inhibition-free template-assisted catalytic organic transformation that takes great advantage of the fact that the product (template) undergoes a termination-free nucleation-elongation assembly (living supramolecular polymerization) under solvent-free conditions. SF-ASP allows for reductive cyclotetramerization of hydrogen-bonding phthalonitriles into the corresponding phthalocyanines in exceptionally high yields (>80%). SF-ASP requires the growing polymer to form hexagonally packed crystalline fibres, which possibly preorganize the phthalonitriles at their cross-sectional edges for their efficient transformation. With metal oleates, SF-ASP produces single-crystalline fibres of metallophthalocyanines again in exceptionally high yields, which grow in both directions without terminal coupling until the phthalonitrile precursors are completely consumed. By taking advantage of this living nature of polymerization, multistep SF-ASP without/with metal oleates allows for the precision synthesis of multi-block supramolecular copolymers.

Applications of Covalent Triazine Polymers in Catalytic Organic Transformations

Among the porous organic polymers, Covalent Triazine Polymers (CTPs) have emerged as an important class of materials with versatile applications such as energy storage and conversion, gas adsorption and separation, photocatalysis and heterogeneous catalysis. Particularly, CTPs have been often used as catalyst/catalyst support due to their excellent thermal and chemical stability, as well as recyclability in catalytic reactions. Moreover, the expanding methods available for the synthesis of CTPs, convenient functionalization and presence of nitrogen sites in the framework make them a suitable candidate to develop catalysts for organic transformations. In this review, the methods of synthesis, characterization of CTPs and mainly their applications as catalyst/ catalyst support in organic transformations are summarized.

Advances in Chiral Metal-Organic and Covalent Organic Frameworks for Asymmetric Catalysis.

Asymmetric catalysis is of crucial importance owing to the huge and rising demand for optically pure substances. Metal-organic frameworks (MOFs) and covalent organic frameworks (COFs), as two emerging crystalline porous materials, have presented great promising applications for heterogeneous asymmetric catalysis. The unique properties, such as, highly regular porous structures, prominent structural tunability, and well-ordered catalytic sites, render chiral MOFs (CMOFs) and chiral COFs (CCOFs) highly active and enantioselective for a large number of asymmetric catalytic organic transformations. Furthermore, they provide a useful platform for facile mechanistic understanding and catalyst design. This review provides an overview of the advancements in CMOFs and CCOFs for asymmetric catalysis. The designs, syntheses and structures of these crystalline porous materials, and their asymmetric catalytic performance are described. And the perspectives on challenges and opportunities in development of CMOFs and CCOFs are discussed. It is anticipated that this review will shed light on the heterogeneous asymmetric catalysis with CMOFs and CCOFs and motivate further research in this promising field.

Understanding and Improving Photocatalytic Activity of Pd-Loaded BiVO4 Microspheres: Application to Visible Light-Induced Suzuki-Miyaura Coupling Reaction.

The effective utilization of visible light is required for exploiting photocatalytic reactions in indoor and outdoor environments. In this study, Pd-supported BiVO4 microspheres (Pd-BiVO4) were prepared for visible light-induced photocatalytic reactions. Under irradiation with a white light-emitting diode, the obtained Pd-BiVO4 composite exhibited considerably improved catalytic activity for the decomposition of an organic dye compared with other BiVO4 catalysts. The Pd-BiVO4 composite was also effective for catalytic organic transformation via the visible light-induced Suzuki-Miyaura coupling reaction. The photogenerated electrons in the conduction band of BiVO4 flowed to the Pd nanoparticles and amplified cross-coupling reaction. The influence of the crystal structure and grain size of BiVO4 and the role of the deposited Pd nanoparticles were fully investigated to elucidate the visible light activity of the catalyst. This system highlights the possibility of an indoor light source with low energy density for sustainable organic transformations.

Ion-exchange Resins and Polypeptide Supported Catalysts: A Critical Review

Heterogeneous catalysis represents one of the important areas in the field of organic synthesis. Major developments have been emerged during last few decades and polymer-supported catalysts have been employed successfully in various catalytic organic transformations. Ion-exchange resins and polypeptides are two important examples of such heterogeneous polymer-supported catalysts among others because of their easy accessibility, stability, recoverability and reusability. Cross-linked ion-exchange resins and polypeptides are highly insoluble, which make them better choice in terms of their easy separation from the reaction mixture and subsequent recyclability. The present review article provides an overview of different types of ion exchange resins as polymer-supported catalysts such as amberlite resin, polystyrene resin, polyionic gel-based systems, ion-exchange resins and prolineimmobilized species, PEG-bound poly (amino acid), amino acid anchored with Merrifild resin, amphiphilic block polypeptides etc. Their preparation, characterizations and catalytic applications in diverse organic transformations have been presented with critical analysis on their stability, mechanistic overview and suitability etc.

Metal‐Metal Cooperation in Dinucleating Complexes Involving Late Transition Metals Directed towards Organic Catalysis

Cooperatively bimetallic organic catalysis, coupling actions of two metal centers in a catalytic organic transformation via co‐activation of a single molecule or synergistic activation of two molecules, has witnessed rapid development in the last decades. This cooperative reacting mode creates new catalytic platforms to facilitate the characterization of bimetallic reaction pathways, offers remarkable improvements to some well‐established reactions, or exhibit unprecedented reactivity. Herein, we demonstrate perspectives of some significant contributions in the field of cooperatively bimetallic organic catalysis using dinucleating complexes with late transition metals. Based on different activation modes for the catalysis, the major advances are classified into: (1) bimetallic co‐activation of small molecules; (2) bimetallic co‐activation of single molecules; (3) bimetallic dual‐activation of two molecules. The mechanisms are also discussed to facilitate the understanding of the way of the metal‐metal cooperation involved in the catalytic cycles.

Surveying Iron–Organic Framework TAL-1-Derived Materials in Ligandless Heterogeneous Oxidative Catalytic Transformations of Alkylarenes

The use of carbonized materials derived from metal–organic frameworks (MOFs) in catalytic organic transformations is less well explored than is the use of MOFs. Here, we survey the oxidative performance of heterogeneous catalyst materials derived from the polycrystalline iron–organic framework TAL-1.

Catalyst as colour indicator for endpoint detection to enable selective alkyne trans-hydrogenation with ethanol

The stereoselective semi-hydrogenation of internal alkynes to E-alkenes is an important, but challenging, transformation, partly because of over-reduction to undesired alkanes. A stop criterion that enables determination of the endpoint of the semi-hydrogenation is thus required to eliminate this over-hydrogenation. Despite its widespread applications in analytic chemistry, the strategy of using colour change for endpoint detection is very rarely applied in catalytic organic transformations. Here we report that an iridium complex catalyses the semi-hydrogenation of internal alkynes using ethanol as the hydrogen donor to afford E-alkenes and ethyl acetate. Importantly, issues of over-reduction and stereoselection have been successfully addressed by using a colour change effect due to the shift of the catalyst resting states, thereby precisely detecting the endpoint of the reaction. This catalytic system is applicable to a wide variety of internal alkynes bearing many auxiliary functional groups, and its utility for synthesis of biologically relevant molecules has been demonstrated. The reduction of alkynes to alkenes is complicated by the potential for over-reduction to the alkane. Here, for the iridium-catalysed semi-hydrogenation of alkynes, the endpoint of the reaction is clearly identified by a colour change of the metal complex.

Valorization of Oceanic Waste Biomass: A Catalytic Perspective.

Efficacious waste utilization is vital in context of sustainability. The past decade has witnessed attempts of usage of land biomass and wastes for various applications, contributing towards a sustainable society. Exploitation of the marine biomass, which does not compete with habitation and food production like land biomass has been largely unnoticed and therefore not being utilized judiciously. Researchers have mainly exploited these resources as functional materials having significant potential applications. However, a catalytic perspective for the valorisation of these polymers arising from oceanic waste widens their scope and ameliorates its use. The objective of the present review is to demonstrate the effectiveness of chitin/chitosan as a catalyst and as a feedstock for deriving important fuels and chemicals. It displays all the reactions heterogeneously catalyzed by them along with the strategic methodology. Their important catalytic organic transformations attempted so far, have also been discussed. The future perspectives are also presented which if inculcated would improve the value addition of the waste, paving a way for greener and imperishable world.

Synthesis and Structures of Stable PtII and PtIV Alkylidenes: Evidence for π-Bonding and Relativistic Stabilization.

Isolable cationic PtII and PtIV alkylidenes, proposed intermediates in catalytic organic transformations, are reported. The bonding in these species was probed by experimental, structural, spectroscopic, electrochemical and computational methods, providing direct evidence for π-bonding, the often-theorized relativistic stabilization of these species, and the influence of oxidation state.

Iron Catalysis in Reduction and Hydrometalation Reactions.

The last two decades have seen an impressive improvement of the use of iron as a fascinating and valuable alternative transition metal in homogeneous catalysis in terms of sustainability and economy. It was efficiently used in catalytic organic synthetic transformations, which in particular include the reduction of unsaturated bonds. This review summarizes the fast development and the recent advances in selective reductions of olefins, alkynes, carbonyl and carboxylic derivatives, imines, and nitro compounds promoted by iron catalysts. The topical hydrogen-borrowing reactions and hydroboration of unsaturated compounds are also reported. It is hoped that this account not only provides an overview of the state of the art in iron catalysis but also stimulates the development of superior greener catalytic systems in the near future.