Recent Progress of Metal Nanoparticle Catalysts for C–C Bond Forming Reactions
TL;DR: In this article, the authors classified and outlined the categories of transition metal NPs by the type of support, such as inorganic materials, magnetically recoverable materials, porous materials, organic-inorganic composites, carbon materials, polymers, and surfactants.
Abstract: Over the past few decades, the use of transition metal nanoparticles (NPs) in catalysis has attracted much attention and their use in C–C bond forming reactions constitutes one of their most important applications. A huge variety of metal NPs, which have showed high catalytic activity for C–C bond forming reactions, have been developed up to now. Many kinds of stabilizers, such as inorganic materials, magnetically recoverable materials, porous materials, organic–inorganic composites, carbon materials, polymers, and surfactants have been utilized to develop metal NPs catalysts. This review classified and outlined the categories of metal NPs by the type of support.
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TL;DR: In this paper , the authors highlight the importance of transition metal nanoparticles in the field of selective carbon-carbon bond-forming reactions such as Suzuki, Heck, and Sonogashira coupling reactions.
6 citations
TL;DR: In this article , the authors survey the unusual cases in which divergent selectivity is controlled by ligands or catalyst speciation, and discuss the remaining challenges and opportunities for the field of site-selective cross-coupling.
Abstract: The vast majority (≥90%) of literature reports agree on the regiochemical outcomes of Pd-catalyzed cross-coupling reactions for most classes of dihalogenated N-heteroarenes. Despite a well-established mechanistic rationale for typical selectivity, several examples reveal that changes to the catalyst can switch site selectivity, leading to the unconventional product. In this Perspective, we survey these unusual cases in which divergent selectivity is controlled by ligands or catalyst speciation. In some cases, the mechanistic origin of inverted selectivity has been established, but in others the mechanism remains unknown. This Perspective concludes with a discussion of remaining challenges and opportunities for the field of site-selective cross-coupling. These include developing a better understanding of oxidative addition mechanisms, understanding the role of catalyst speciation on selectivity, establishing an explanation for the influence of ring substituents on regiochemical outcome, inverting selectivity for some "stubborn" classes of substrates, and minimizing unwanted over-reaction of di- and polyhalogenated substrates.
5 citations
TL;DR: In this article , cellulose nanocrystals were isolated from corn leaf via chemical treatment involving alkalizing, bleaching and acid hydrolysis, and the crystallinity of obtained cellulose was evaluated in each step, focusing on the effects of reactant concentration and reaction time.
Abstract: As the most abundant natural biopolymer on earth, celluloses have long-term emerged as a capable platform for diverse purposes. In the context of metal nanoparticles applied to catalysis, the alternatives to traditional catalyst supports by using biomass-derived renewable materials, likely nanocelluloses, have been paid a great effort, in spite of being less exploited. In this study, cellulose nanocrystals were isolated from corn leaf via chemical treatment involving alkalizing, bleaching and acid hydrolysis. The crystallinity of obtained cellulose was evaluated in each step, focusing on the effects of reactant concentration and reaction time. Cellulose nanocrystals were characterized by powder X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), evidencing the presence of cellulose nanospheres (crystallinity index of 67.3% in comparison with 38.4% from untreated raw material) in the size range of 50 nm. Without using any additional surfactants or stabilizers, silver nanoparticles (AgNPs) well-dispersed on the surface of cellulose nanocrystals (silver content of 5.1 wt%) could be obtained by a simple chemical reduction using NaBH4 at room temperature. The catalytic activity was evaluated in the selective reductions of 4-nitrophenol towards 4-aminophenol and methyl orange towards aromatic amine derivatives in water at room temperature. The effects of catalyst amount and reaction time were also studied in both reduction processes, showing near-quantitative conversions within 5 minutes and obeying the pseudo-first-order kinetics, with the apparent kinetic rate constants of 8.9 × 10−3 s−1 (4-nitrophenol) and 13.6 × 10−3 s−1 (methyl orange). The chemical structure of the catalytic system was found to be highly stable during reaction and no metal leaching was detected in reaction medium, evidencing adaptability of cellulose nanocrystals in immobilizing noble metal nanoparticles.
3 citations
TL;DR: In this article , Covalent triazine frameworks (CTFs) with structure designability and multifunctionalities have aroused increasing attention in conventional thermocatalysis and modern photocatalysis/electrocatalysis.
Abstract: Covalent triazine frameworks (CTFs) with structure designability and multifunctionalities have aroused increasing attention in conventional thermocatalysis and modern photocatalysis/electrocatalysis. However, many obstacles still exist on the road to simultaneously achieving...
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TL;DR: This Review will compare the results obtained from different systems and try to give a picture on how different types of metal species work in different reactions and give perspectives on the future directions toward better understanding of the catalytic behavior of different metal entities in a unifying manner.
Abstract: Metal species with different size (single atoms, nanoclusters, and nanoparticles) show different catalytic behavior for various heterogeneous catalytic reactions. It has been shown in the literature that many factors including the particle size, shape, chemical composition, metal–support interaction, and metal–reactant/solvent interaction can have significant influences on the catalytic properties of metal catalysts. The recent developments of well-controlled synthesis methodologies and advanced characterization tools allow one to correlate the relationships at the molecular level. In this Review, the electronic and geometric structures of single atoms, nanoclusters, and nanoparticles will be discussed. Furthermore, we will summarize the catalytic applications of single atoms, nanoclusters, and nanoparticles for different types of reactions, including CO oxidation, selective oxidation, selective hydrogenation, organic reactions, electrocatalytic, and photocatalytic reactions. We will compare the results o...
2,700 citations
TL;DR: In this article, a template synthesis strategy for preparing Cu nanoclusters within dendrimer 'nanoreactors' is demonstrated, where Cu(2+) ions are first quantitatively sorbed into the dendromer via a strong coordinative interaction with interior amines and then chemically reduced to yield Cu nanclusters.
Abstract: : A new template synthesis strategy for preparing Cu nanoclusters within dendrimer 'nanoreactors' is demonstrated. Hydroxyl-terminated polyamidoamine (PAMAM) dendrimers of generation higher than 2 act as monodispersed templates as well as stabilizers for nanocluster synthesis. Cu(2+) ions are first quantitatively sorbed into the dendrimer via a strong coordinative interaction with interior amines and then chemically reduced to yield Cu nanoclusters. The nanoclusters are composed of a well-defined number of atoms. Importantly, cluster size can be controlled by varying the size of the host dendrimer nanoreactor (16-atom Cu cluster in G4 and 64-atom Cu cluster in G6 dendrimers). The clusters remain trapped within the dendrimers for extended periods of time, do not agglomerate, and do not precipitate. The clusters can also be oxidized to yield dendrimer-encapsulated Cu(2+).
889 citations
TL;DR: This review provides a critical overview on recent applications of Pd metal catalysts in cross-couplings and related reactions, with particular attention to the discussion of the mechanistic pathways that have been proposed to explain the catalytic role of PD metal.
Abstract: Cross-couplings and related reactions are a class of highly efficient synthetic protocols that are generally promoted by molecular Pd species as catalysts. However, catalysts based on more or less highly dispersed Pd metal have been also employed for this purpose, and their use, which was largely limited to the Heck reaction until the turn of the century, has been extended in recent years to most reactions of this class. This review provides a critical overview on these recent applications of Pd metal catalysts. Particular attention is devoted to the discussion of the mechanistic pathways that have been proposed to explain the catalytic role of Pd metal. Furthermore, the most outstanding Pd metal based catalytic systems that have emerged are illustrated, together with the development of novel approaches to boost the reactivity of Pd metal. A section summarizing the current industrial applications of Pd metal catalyzed reactions of this kind concludes the review.
782 citations
644 citations
TL;DR: The as-prepared COF-supported ultrafine Pt NPs and Pd NPs show excellent catalytic activity respectively in nitrophenol reduction and Suzuki-Miyaura coupling reaction under mild conditions and low catalyst loading.
Abstract: Covalent organic frameworks (COFs) with well-defined and customizable pore structures are promising templates for the synthesis of nanomaterials with controllable sizes and dispersity. Herein, a thioether-containing COF has been rationally designed and used for the confined growth of ultrafine metal nanoparticles (NPs). Pt or Pd nanoparticles (Pt NPs and Pd NPs) immobilized inside the cavity of the COF material have been successfully prepared at a high loading with a narrow size distribution (1.7 ± 0.2 nm). We found the crystallinity of the COF support and the presence of thioether groups inside the cavities are critical for the size-controlled synthesis of ultrafine NPs. The as-prepared COF-supported ultrafine Pt NPs and Pd NPs show excellent catalytic activity respectively in nitrophenol reduction and Suzuki–Miyaura coupling reaction under mild conditions and low catalyst loading. More importantly, they are highly stable and easily recycled and reused without loss of their catalytic activities. Such COF...
458 citations