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Metallodendrimers containing redox-robust centres may have applications in molecular redox recognition, sensing, biosensing and catalysis. So far, however, no metallodendrimer is known in several oxidation states. Here we report metallodendrimers with two electronically communicating iron centres that are stable and isolated in both the Fe(II) and Fe(III) oxidation states, and in addition as class-II mixed-valent Fe(II)Fe(III) complexes. These dendrons are branched to arene-centred dendrimer cores either by Sonogashira coupling or 'click' reactions. The latter reaction involves the introduction of intradendritic 1,2,3-triazolyl ligands, which allows investigation of the selective role of these ligands in intradendritic Au(III) coordination and Au(0) nanoparticle stabilization. As a result, and using the various metallodendrimers with different oxidation states, small Au(0) nanoparticles are intradendritically stabilized by the triazole ligands, whereas with the related non-'click' dendrimers large Au(0) nanoparticles are formed outside the dendrimers and stabilized by a group of dendrimers.

The extraordinary development of the design and synthesis of dendrimers has allowed scientists to locate redox sites at precise positions (core, focal points, branching points, termini, cavities) of these perfectly defined macromolecules, which have generation-controlled sizes and topologies matching those of biomolecules. Redox-dendrimer engineering has led to fine modelling studies of electron-transfer metalloproteins, in which the branches of the dendrimers hinder access to the active site in a manner reminiscent of that of the protein. It has also enabled the construction of remarkable catalysts, sensors and printboards, including by sophisticated design of the interface between redox dendrimers and solid-state devices - for example by functionalizing electrodes and other surfaces. Electron-transfer processes between dendrimers and a variety of other molecules hold promising applications in diverse areas that range from bio-engineering to sensing, catalysis and energy materials.

This article is an account of the work carried out in the authors' laboratory illustrating the usefulness of dendrimer design for nanoparticle palladium catalysis. The "click" synthesis of dendrimers constructed generation by generation by 1-->3 C connectivity, introduces 1,2,3-triazolyl ligands insides the dendrimers at each generation. Complexation of the ligands by Pd(II) followed by reduction to Pd(0) forms dendrimer-stabilized Pd nanoparticles (PdNPs) that are extremely reactive in the catalysis of olefin hydrogenation and C-C bond coupling reactions. The stabilization can be outer-dendritic for the small zeroth-generation dendrimer or intra-dendritic for the larger first- and second-generation dendrimers. The example of the Miyaura-Suzuki reaction that can be catalyzed by down to 1 ppm of PdNPs with a "homeopathic" mechanism (the less, the better) is illustrated here, including catalysis in aqueous solvents.

Water-soluble arene-cored "clicked" and non-"clicked" dendrimers terminated by 27, 81, and 243 triethyleneglycol (TEG) tethers (respectively generations G0, G1, and G2) have been synthesized and shown to form dendrimer-encapsulated gold nanoparticles (DEAuNPs) and dendrimer-stabilized gold nanoparticles (DSAuNPs). The dendrimers have been characterized by IR, (1)H NMR, (13)C NMR, size-exclusion chromatography, elemental analysis, MALDI-TOF mass spectroscopy, DOSY NMR, and dynamic light scattering. The AuNPs have been generated and stabilized by these PEGylated dendrimers using a variety of reduction modes, including NaBH(4) in methanol, various single-electron metallocene-type reductants, and even in the absence of additional reductants. The active role of the "clicked" triazole rings, dendrimer generation, stoichiometry of Au precursor, and nature of the reductant and of the solvent are delineated, leading to DSAuNPs with the G0 dendrimer and smaller DEAuNPs with the G1 and G2 dendrimers. Altogether, AuNPs in the size range from 1.8 to 42 nm were formed and characterized by transmission electron microscopy (TEM), high resolution TEM (HRTEM) and UV-vis spectroscopy. Both 1,2,3-triazole and PEGylated Percec-type dendrons are required in the dendrimer structure for the stabilization of AuNPs upon NaBH(4) reduction of HAuCl(4) in methanol. On the other hand, in the absence of other reductant in water, only PEGylated Percec-type dendrons in dendrimers were found to be indispensable, because of their semicavitand shape, for the spontaneous reduction of HAuCl(4) and stabilization of DSAuNPs.

Highly catalytically active core–shell nanoparticles (NPs) have attracted great attention towards applications. Herein, core–shell Au@AgNPs were simply obtained via a green and cheap one-step method using tannic acid (TA) as both a reductant and a stabilizer. TA was used to cross-link poly(vinyl alcohol) (PVA), forming a PVA/TA hydrogel with the repeated freezing–thawing method. The gelation mechanism was confirmed by urea-treatment experiment, UV-vis, IR, TG, and DSC. The freezing–thawing treatment endows TA and PVA with better conditions to form hydrogen bonds, and the intensive hydrogen bond interactions and weak crystallization interactions work in synergy to maintain the three-dimensional network of the PVA/TA hydrogel. Owing to favorable mechanical properties and suitable pore size, the PVA/TA hydrogel further served as a support for the immobilization of Au@AgNPs that exhibited excellent and recyclable catalytic degradation ability for 4-nitrophenol, 2-nitrophenol, methylene blue, and Congo red. [ABSTRACT FROM AUTHOR]

Sodium borohydride hydrolysis catalyzed by composite nanomaterials has long been proposed as a viable possibility for hydrogen generation, but it required either expensive noble metals or sophisticated composites. Herein, the catalysis of NaBH4 hydrolysis is studied with single earth‐abundant Fe, Co, Ni, and Cu nanoparticles supported by a metal organic framework (MOF), ZIF‐8. It appears that CoNPs@ZIF‐8 is the most efficient and selective catalyst in this series. The turnover frequency (TOF) related to the total atoms number within the cobalt nanoparticles reaches 14000 mLH2 min−1 gCo−1 at 30 °C, and the TOF(s) related to the number of surface atoms of the cobalt nanoparticles 19400 mLH2 min−1 gCo−1 at 30 °C. Kinetic studies including a high kinetic isotope effect disclosed using D2O (kH/kD=6.85) and the favorable effect of NaOH lead to the suggestion of an oxidative addition of a O−H bond of water in the rate‐determining step. Earth‐abundant nanocatalyst: CoNPs@ZIF‐8 showed excellent efficiency and selectivity in the hydrolysis of NaBH4 for the generation of H2. The performance of this nanocatalyst is better than those of most non‐noble metal catalysts, and even some noble metal catalysts. [ABSTRACT FROM AUTHOR]

Abstract: Click ferrocenyl‐terminal dentromers, a family of arene‐cored dendrimers with triple branching (9‐Fc, 27‐Fc, 81‐Fc, and 243‐Fc), reduce AuIII to ferricinium dentromer‐stabilized Au nanoparticles (AuNPs). Cyclic voltammetry studies in CH2Cl2 show reversible CV waves with some adsorption for the 243‐Fc dentromer and the number of redox groups found, 255±25, by using the Bard–Anson method, is close to the theoretical number of 243. The dentromers reduce aqueous HAuCl4 to water‐soluble ferricinium chloride dentromer‐stabilized AuNPs with core sizes between 30 and 47 nm. These triazolylferricinium dentromer‐stabilized AuNPs are reduced by cobaltocene to cobalticinium chloride and ferrocene dentromer weakly stabilized AuNPs together with a redshift of the AuNP plasmon. The weakness of the AuNP stabilization is characterized by dentromer extraction with CH2Cl2 along with irreversible AuNP agglomeration for the 9, 27, and 81‐ferrocenyl dentromer, with only the 243‐ferrocenyl dentromer‐AuNP withstanding this process. Altogether, this demonstrates the electronic switching of the dentromer‐mediated AuNP stabilization. [ABSTRACT FROM AUTHOR]

Graphene-based nanomaterials are promising in a wide range of applications due to their unique structural, chemical and physical properties that have recently led to their investigations as co-catalysts and nanoparticle catalyst templates for organic, electrochemical and photochemical reactions. Herein, we present an overview of hybrid metal nanoparticle-graphene catalysts with specific attention to the most recent achievements since 2015. The state-of-the-art of their synthesis and characterization is also summarized, and the synergistic metallic nanoparticle-graphene interactions and their functions in catalysis are discussed. Finally, challenges and future outlooks for this hot area are envisaged. [ABSTRACT FROM AUTHOR]

Abstract: Nanoparticles (NPs) are actively investigated for their efficient use in catalysis, but their means of synthesis is a key factor influencing their catalytic properties owing to surface coverage with byproducts. Here, neutral electron‐ and hydride‐rich late transition metal organometallics are compared for the synthesis of late transition metal NPs in the presence of poly(vinylpirolidone) (PVP). In particular, the effect of electron‐reservoir donors, hydride‐reservoir donors, and electron‐rich dimers yielding NPs electrostatically stabilized by cationic organometallics are compared in terms of NP size and catalytic efficiency. The catalytic reactions scrutinized with excellent results include 4‐nitrophenol reduction to 4‐aminophenol by NaBH4 for the AuNPs and PdNPs, and Suzuki–Miyaura reactions for the PdNPs. The nature of the reductant has more influence on the NP size in the case of AuNPs than PdNPs, and the best NP catalysts are obtained with hydride‐reservoir complexes as reductants. The less bulky hydride donors are superior, with the complex [CoCp(ŋ4‐C5H6)] (Cp=ŋ5‐C5H5) giving the NPs with the best catalyst efficiencies for both reactions. Protection of the NP cores by the organometallic sandwich salt is found to be the key to catalytic efficiency. [ABSTRACT FROM AUTHOR]

Preservation from easy aerobic Cu(0) oxidation in Cu nanoparticles (NPs) is of interest for electronic, sensing, optical and catalytic properties. An anti-galvanic (AG) method is presented here for this purpose. Remarkably, alloying CuNPs with AuNPs or AgNPs followed by exposure to air only leads to Cu(0) oxidation to Cu(i) in AgCu alloyed NPs, whereas Cu(0) is not oxidized in AuCu alloyed NPs in which Au(i) forms. This result is also verified by “click” catalysis experiments. [ABSTRACT FROM AUTHOR]

A ligand design is proposed for transition metal nanoparticle (TMNP) catalysts in aqueous solution. Thus, a tris(triazolyl)-polyethylene glycol (tris-trz-PEG) amphiphilic ligand, 2, is used for the synthesis of very small TMNPs with Fe, Co, Ni, Cu, Ru, Pd, Ag, Pt, and Au. These TMNP- 2 catalysts were evaluated and compared for the model 4-nitrophenol reduction, and proved to be extremely efficient. High catalytic efficiencies involving the use of only a few ppm metal of PdNPs, RuNPs, and CuNPs were also exemplified in Suzuki-Miyaura, transfer hydrogenation, and click reactions, respectively. [ABSTRACT FROM AUTHOR]

We report the first pentamethylferrocene (PMF) polymers and the redox chemistry of their robust polycationic pentamethylferricenium (PMFium) analogues. The PMF polymers were synthesized by ring-opening metathesis polymerization (ROMP) of a PMF-containing norbornene derivative by using the third-generation Grubbs ruthenium metathesis catalyst. Cyclic voltammetry studies allowed us to determine confidently the number of monomer units in the polymers through the Bard-Anson method. Stoichiometric oxidation by using ferricenium hexafluorophosphate quantitatively and instantaneously provided fully stable (even in aerobic solutions) blue d5 FeIII metallopolymers. Alternatively, oxidation of the PMF-containing polymers was conducted by reactions with AgI or AuIII, to give PMFium polymer-embedded Ag and Au nanoparticles (NPs). In the presence of I2, oxidation by using AgI gave polymer-embedded Ag/AgI NPs and AgNPs at the surface of AgI NPs. Oxidation by using AuIII also produced an AuI intermediate that was trapped and characterized. Engineered single-electron transfer reactions of these redox-robust nanomaterial precursors appear to be a new way to control their formation, size, and environment in a supramolecular way. [ABSTRACT FROM AUTHOR]

Modern methods that involve intradendritic catalysis are introduced in this feature article. Supramolecular principles, therefore, derive from the concept of the unimolecular dendritic micelle introduced by Newkome. When the micellar effect is combined with intradendritic ligand acceleration, copper(I) catalysts or palladium nanoparticles (PdNPs) are required at the ppm level for efficient reactions. Applications range from organic catalysis to catalysis by metal complexes of intradendritic ligands and dendrimer-stabilized nanoparticles (NPs) that are located at the dendrimer core or between the dendrimer tethers. Bimetallic nanoparticle-cored dendrimers including superparamagnetic iron oxide nanoparticles (SPIONs) are especially promising due to very facile magnetic separation. [ABSTRACT FROM AUTHOR]

Four different triazolylbiferrocenyl-containing polymers were used for the stabilization of palladium nanoparticles (PdNPs) upon reducing triazole-coordinated Pd(II) both in organic solvents and in water. The resulting PdNPs were active in the Suzuki-Miyaura coupling of bromoaromatics even with down to only 20 ppm of Pd. The comparison between the four different polymer-stabilized PdNPs allows concluding that a flexible polyethylene glycol moiety in the linear triazolylbiferrocenyl polymer permits a better stabilization of the PdNPs than polymers containing triazolylbiferrocenyl side chains with a rigid styrene or succinimide moieties. [ABSTRACT FROM AUTHOR]

The simple impregnation of γ-Fe2O3(core)/SiO2(shell) magnetic nanoparticles with a dendrimer that contains stabilized Pd nanoparticles is presented as a new method to produce highly efficient heterogeneous catalysts. This technique provides much better stability, recyclability, and activity in CC cross-coupling reactions and selective oxidation of benzyl alcohol to benzaldehyde in water than unsupported Pd nanoparticles. [ABSTRACT FROM AUTHOR]

Various types of mixed-valent metallodendrimers and star-shaped macromolecules containing ferrocenyl, biferrocenyl, or other redox-robust iron groups with rigid or flexible tethers of short and long lengths mostly studied in the authors’ laboratory including the class type in terms of Robin-Day classification and their functions including electrode modification, sensing, and nanoparticle templates are discussed in this mini review. [ABSTRACT FROM PUBLISHER]

Palladium nanoparticles stabilized by glycodendrimers (PdDSNs) in water were prepared by coordination of PdII to intradendritic triazole ligands upon reaction of K2PdCl4 with the dendrimer in water followed by aqueous NaBH4 reduction to Pd0. TEM images show that the PdDSNs are small (average diameter: 2.3 nm) and relatively monodisperse owing to a low concentration of metal precursor. The catalytic activity of these PdDSNs was evaluated for the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) by NaBH4 (only 0.2 mol-% of Pd per mol substrate is used) and for the Miyaura-Suzuki C-C coupling with various substituted aryl bromides (only 0.01 mol-% of Pd per mol substrate is used). Comparisons of the catalytic activities of these PdDSNs with those of larger PdDSNs (diameter: 14 nm) reveal that smaller NPs catalyze faster 4-NP reduction than their larger counterparts but lack any notable surface dependency for Suzuki-Miyaura catalysis. [ABSTRACT FROM AUTHOR]

Simple 'click' polycondensation metallopolymers of redox-robust bis(ethynyl)biferrocene (biFc) and di(azido) poly(ethylene glycol) (PEG400 and PEG1000) were designed for multiple functions including improvement of water solubility and biocompatibility, the introduction of mixed valency and sensing capabilities, and as nanoparticle stabilizers for catalysis. [ABSTRACT FROM AUTHOR]

A large family of bifunctional 1,2,3-triazole derivatives that contain both a polyethylene glycol (PEG) chain and another functional fragment (e.g., a polymer, dendron, alcohol, carboxylic acid, allyl, fluorescence dye, redox-robust metal complex, or a β-cyclodextrin unit) has been synthesized by facile 'click' chemistry and mildly coordinated to nanogold particles, thus providing stable water-soluble gold nanoparticles (AuNPs) in the size range 3.0-11.2 nm with various properties and applications. In particular, the sensing properties of these AuNPs are illustrated through the detection of an analogue of a warfare agent (i.e., sulfur mustard) by means of a fluorescence 'turn-on' assay, and the catalytic activity of the smallest triazole-AuNPs (core of 3.0 nm) is excellent for the reduction of 4-nitrophenol in water. [ABSTRACT FROM AUTHOR]

Air-stable gold nanoparticles stabilized by glycodendrimers (AuDSNs) in water were prepared in the presence of a reducing agent, NaBH4. A UV/Vis spectroscopy study demonstrates that no spontaneous reduction of Au3+ ions occurs in the presence of glycodendrimers. The AuDSNs were characterized by UV/Vis spectroscopy and transmission electron microscopy (TEM). TEM images show that the AuDSNs were very small (average diameter: 2.6 nm). The catalytic activity of these AuDSNs was evaluated for the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) by NaBH4 monitored by UV/Vis spectroscopy. Studies of the reduction reaction reveal that the rate constant depends on the concentration of 4-NP. [ABSTRACT FROM AUTHOR]

Nanoparticle-supported tris(triazolyl)-CuBr, with a diameter of approximately 25 nm measured by TEM spectroscopy, has been easily prepared, and its catalytic activity was evaluated in the copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction. In initial experiments, 0.5 mol % loading successfully promoted the CuAAC reaction between benzyl azide and phenylacetylene, in water at room temperature (25 °C). During this process, the iron oxide nanoparticle-supported tris(triazolyl)-CuBr displayed good monodispersity, excellent recoverability, and outstanding reusability. Indeed, it was simply collected and separated from the reaction medium by using an external magnet, then used for another five catalytic cycles without significant loss of catalytic activity. Inductively coupled plasma (ICP) analysis for the first cycle revealed that the amount of copper leached from the catalyst into the reaction medium is negligible (1.5 ppm). The substrate scope has been examined, and it was found that the procedure can be successfully extended to various organic azides and alkynes and can also be applied to the one-pot synthesis of triazoles, through a cascade reaction involving benzyl bromides, alkynes, and sodium azide. In addition, the catalyst was shown to be an efficient CuAAC catalyst for the synthesis of allyl- and TEG-ended (TEG=triethylene glycol) 27-branch dendrimers. [ABSTRACT FROM AUTHOR]

The article presents a research that examines the homeopathic catalytic activity and atom-leaching mechanism in Miyaura-Suzuki reactions based on ambient conditions with precise dendrimer-stabilized palladium nanoparticles (PdNPs). As per mechanistic investigations, all catalytic steps in hydrogenation mechanism occur on the PdNP surface. It concludes that the development of Pd is slower than other quenching mechanism and does not limit yields of the reactions catalyzed by alkyl thiolate PdNPs.

Palladium nanoparticles (size=1.6±0.3 nm) stabilized by a polyethylene glycol containing triazolyl rings, synthesized by click reaction in water, are efficient catalysts for the Suzuki-Miyaura coupling of bromoarenes in aqueous ethanol and the borohydride reduction of 4-nitrophenol in water. Turnover numbers (TONs) reach 99,000 and turnover frequencies (TOFs) are up to 198,000 h−1 for the CC cross coupling reactions in water/ethanol. [ABSTRACT FROM AUTHOR]

Highlights: [•] Overview of basic concepts, seminal studies, recent progress and breakthroughs in dendritic catalysis. [•] Locations of catalytic entities include core, periphery, nanoparticles and building block. [•] Metallodendritic catalysts, dendrimer-stabilized nanoparticle catalysts and dendritic organocatalysts. [•] Essential new concepts have emerged with various positive and negative dendritic effects. [Copyright &y& Elsevier]

Mono-, bis-, and tris(4-ferrocenyl-1,2,3-triazolylmethyl)arene-β-cyclodextrin adducts have been used to prepare new Pd0 nanoparticle (PdNP) catalysts for C-C cross-coupling reactions in EtOH/H2O. The results show that these catalysts work well in Miyaura-Suzuki and Heck reactions with iodoarenes at 25 and 80 °C, respectively, with turnover numbers (TONs) of up to 31000 for standard Miyaura-Suzuki reactions of PhI when 10 ppm of the Pd catalyst (5 nm PdNPs) were used. The results show the benefit for PdNP catalysis of encapsulating hydrophobic catalytic systems between peripheral water-solubilizing cyclodextrins as bolamphiphile-like materials because the open monoferrocenyltriazolylmethylbenzene system shows a considerably reduced catalytic efficiency compared with bis- and tris(4-ferrocenyl-1,2,3-triazolylmethyl)arene-β-cyclodextrin adducts. [ABSTRACT FROM AUTHOR]

lkyne protection by complexation of ethynylferrocene with dicobalt octacarbonyl followed by regioselective acetylation, then deprotection and “click” reaction with a nona-azido-terminated arene-cored dendrimer leads to the heterodifunctional nona(1,2,3-triazolyl-acetylferrocenyl) dendrimer. Cyclic voltammetry of this metallodendrimer shows recognition of both ATP and Pd. HAuCl is reduced much more slowly to gold nanoparticles by the nona(triazolyl-acetylferrocenyl dendrimer than by the nona(triazolylferrocenyl) dendrimer due to the shift of redox potential in the new heterodifunctional dendrimer compared to that of the parent ferrocenyl dendrimer. [ABSTRACT FROM AUTHOR]

Abstract: Dendritic Pd catalysts, dendrimer-stabilized Pd nanoparticle (PdNP) catalysts, and their comparison and combined use for carbon–carbon coupling reactions are discussed with emphasis on the research carried out in the author’s laboratory during the last decade. Multinuclear star-shaped catalysts rather than dendritic catalysts can reach the efficiency of the best monometallic catalysts, whereas PdNPs stabilized by dendrimers can react with turnover numbers close to 106 and bring useful mechanistic indications. In both areas, leaching issues are examined. Finally, results of the literature in asymmetric Pd catalysis by chiral dendrimers and Pd nanoparticles stabilized by chiral ligands are also reviewed, revealing the importance of the dendritic and molecular ligand design and the role of leaching Pd atoms. [ABSTRACT FROM AUTHOR]

Small aminosilica nanoparticles (NPs, 12 nm SiO2core) were covered with ferrocenyl (Fc) and pentamethylferrocenyl (Fc*) groups by reactions with metallocenyl carbonyl chlorides. Cyclic voltammetry in methanol/acetonitrile showed a single fully chemically- and electrochemically-reversible wave with a diffusion-controlled current; colorimetric titrations with [FcCOMe][BF4] of the Fc-SiO2and Fc*-SiO2NPs indicated a coverage of the aminosilica NPs of 335 ? 50 Fc or 240 ? 40 Fc* groups. [ABSTRACT FROM AUTHOR]

This micro-review shows how a simple but powerful organometallic C-H activation could be made very useful for the construction of a large variety of stars, dendritic cores, dendrons and dendrimers of variable sizes including giant dendrimers and gold-nanoparticle-cored dendrimers. The synthesis of ferrocenyl-terminated dendrimers was then achieved by reactions of chlorocarbonylferrocene with polyamino dendrimers, ferrocenylsilylation of polyolefin dendrons and dendrimers and 'click' reactions of ferrocenyl acetylene with azido-terminated dendrimers. The functions of these metallodendrimers include molecular electronics (molecular batteries), molecular redox recognition and sensing and catalysis using dendritic stabilization of nanoparticle catalysts. [ABSTRACT FROM AUTHOR]

Examines the assembly, supramolecular chemistry, quantum-size-related properties of gold nanoparticles and its applications toward biology, catalysis, and nanotechnology. Maintenance of the spheroid suspension; Improvement of the synthesis of Schmid's cluster; Causes of the formation of of the microemulsion; Extraction of metal ions from the aqueous phase to the organic phase; Synthesis of the bimetallic nanoparticles.

The research recently carried out in our laboratories is summarized and discussed in the literature context towards green chemistry (dendritic catalysts) and nanotechnology: (i) construction of giant dendrimers far beyond the De Gennes dense-packing limit using building blocks efficiently synthesized by organo-iron activation of simple arene; (ii) use of water-soluble star-shaped organo-iron redox catalysts for nitrate and nitrite cathodic reduction in water; (iii) synthesis of giant dendritic stars from three generations of ruthenium-carbene dendrimers using ROMP and remarkable dendritic effects; (iv) assembly of dendronized gold nanoparticles that selectively recognized H2PO4– and ATP2–; (v) electron-reservoir metallodendrimers serving as molecular batteries and the example of C60. To cite this article: D. Astruc et al., C. R. Chimie 6 (2003). [Copyright &y& Elsevier]

Palladium nanoparticles (PdNPs) with a size of 1.4 nm are stabilized by dendritic nanoreactors containing 1,2,3-triazole ligands with hydrophilic triethylene glycol (TEG) termini. These PdNPs are stable for months under air and are extremely active for the Suzuki–Miyaura reactions of aryl bromides down to sub-ppm levels. [ABSTRACT FROM AUTHOR]

A magnetically separable ruthenium catalyst was synthesized through immobilizing a pentamethylcyclopentadienyl ruthenium complex on iron oxide nanoparticles. The catalyst is highly active and selective for the synthesis of 1,5-disubstituted 1,2,3-trizoles via cycloaddition of alkynes and organic azides and can be recycled at least 5 times. [ABSTRACT FROM AUTHOR]

[Display omitted] Unsaturated furanic aldehydes are derived from lignocellulosic biomass resources and subsequently used to produce valuable chemicals. However, the highly efficient, selective hydrogenation of the biomass-derived unsaturated furan C O bond remains challenging. Here we report that graphene-like nitrogen doped porous carbon (GNPC) nanosheets are synthesized from carbon-rich, sustainable, and renewable biomass precursors (glucose, fructose and 5-hydroxymethylfurfural, HMF) with high surface areas, large pore volumes and narrow mesopores. GNPC derived from HMF is an excellent catalyst support for PtCo nanoparticles with ultrafine nanoparticles size and homogeneous distributions. This catalyst is highly efficient for hydrogenation of biomass-derived furan-based unsaturated aldehydes, with high yields, to the corresponding unsaturated alcohols under mild conditions. This design strategy should further allow the development of selective, simple, green heterogeneous catalysts for challenging chemical transformations. [ABSTRACT FROM AUTHOR]

Dendronized polymers (DPs) are an increasing field at the interfaces between organic chemistry, polymer synthesis, and materials science, and in particular DPs are expected to provide designed applications as nanoparticle (NP) sensors and catalysts. Herein, we report a new highly-branched amphiphilic dendronized diblock copolymer containing bulky hydrophilic triethylene glycol (TEG) and hydrophobic ferrocenyl (Fc) groups via the living and controlled ring-opening metathesis polymerization. The amphiphilicity drives the self-assembly of the resulting DP into spherical nanoscale micelles in water using THF or DMSO as cosolvents. AuNPs and AgNPs of various sizes depending on the presence of NaBH 4 are successfully prepared using the DP as stabilizers or reductants and used as excellent catalysts for the reduction of 4-nitrophenol (4-NP) to 4-aminophenol by NaBH 4. The obtained AuNPs about 2.1 nm show TONs up to 25 000 and TOFs of 26 400 h−1 and remain stable and efficient for this catalysis after two months. Highly-branched amphiphilic ferrocenyl-containing dendronized diblock copolymer is prepared by ROMP and used as stabilizers or reductants to synthesize AuNPs and AgNPs for high-efficiency catalysis in 4-nitrophenol reduction. Image 1 • Ferrocenyl dendronized diblock copolymer is synthesized by ROMP. • Dendronized copolymer can self-assemble into nanoscale spherical micelles. • Dendronized copolymer can be used as reducing and stabilizing agents for AuNPs/AgNPs. • AuNPs and AgNPs show high catalytic activity for 4-nitrophenol reduction. • AuNPs and AgNPs show long-term stability and efficiency for catalysis. [ABSTRACT FROM AUTHOR]

Review: 158 refs. [ABSTRACT FROM AUTHOR]

Examines the properties of supramolecular gold nanoparticles for the redox recognition of oxoanions. Synthesis of amidoferrocenyl alkanethiol gold colloids by ligand substitution; Utilization of colloids in sensors; Influence of Cp stereoelectronic effects on redox recognition properties.

Abstract: Palladium based dendrimer-encapsulated metal nanoparticles (DEMNs) are prepared by reduction of an aqueous solution of palladium (II) and five generations of amino terminated dendrimers (DAB (diaminobutane) dendrimers). The average size of the palladium nanoparticles formed is 1.7–2.8nm. Catalytic performances of these DEMNs have been studied in the Suzuki cross-coupling reaction. [Copyright &y& Elsevier]

Janus molecular architectures have recently attracted attention due to their structures and properties that differ from those of traditional symmetric structures. Herein, two new small redox-reversible mixed-dendron star-shape molecules containing three ferrocenyl groups have been synthesized by linking two distinct dendrons using an esterification reaction. These organometallic nano structures were characterized by 1 H and 13 C NMR, MS, IR and UV–vis. spectroscopies and cyclic voltammetry confirming the number of ferrocenyl groups and AFM and DLS showing micellar assemblies. Au and Ag nanoparticles were stabilized in the presence of a mixed-dendron structure having amidoferrocene termini upon reaction of the nanoparticle metal precursor with NaBH 4 . Compared reactions of the two star-molecules with HAuCl 4 showed a slow redox reaction leading to Au nanoparticles only with the star-molecule terminated with triazolyferrocene termini, which is taken into account by the difference of their redox potentials. [ABSTRACT FROM AUTHOR]

• Recent advances on nanoparticles for NRR are summarized. • Fundamentals of NRR and brief theoretical calculations are discussed. • Strategies for boosting the intrinsic catalytic properties of the NRR are outlined. • The challenges, perspectives, and research directions in NRR are highlighted. Ammonia is an essential raw ingredient for fertilizers, a carbon-free hydrogen carrier, and an alternative fuel. The natural process of producing ammonia cannot meet the rapidly growing global demand. On the other hand, the conventional industrial Haber-Bosch process for ammonia production demands high energy and generates massive greenhouse gases. Recently, the research community has focused on designing environmentally friendly nanocatalysts for the electrocatalytic N 2 reduction reaction (NRR) that involves less energy consumption. However, the NRR is still far from industrial implementation because of the low faradic efficiency and ammonia formation rate. In this comprehensive review, we start with a brief overview of the fundamentals of NRR related to thermodynamic perspectives and discuss the reaction mechanisms for ammonia synthesis. We then critically introduce the research methods for electrocatalytic NRR and various nanocatalysts, including transition metals, non-metals, main group elements, and noble-metal-based NRR electrocatalysts. Finally, some outlooks are provided on the research progress of the NRR electrocatalytic nanomaterials, methods and techniques toward ammonia production. [ABSTRACT FROM AUTHOR]

Reports on the influence of supramolecular assemblies on the recognition of H[sub 2]PO[sub 4][sup -]. Recognition of small anions using metallodendrimers and gold nanoparticles as exoreceptors; Assembly of redox-active metallodendrimers by multiple H-bonding that can possibly benefit from positive dendritic effects.

Abstract: A new water-soluble glycodendrimer containing 9 terminal modified xylose branches was prepared from nona-azide terminated dendrimer by ‘click’ chemistry. The glycodendrimer was analyzed by 1H, 13C NMR and mass spectroscopy and used to stabilize palladium (PdNPs) and platine (PtNPs) nanoparticles. These DSN are stable in water and were characterized by TEM. The platinum NPs showed a remarkable catalytically activity for olefin hydrogenation in water at room temperature. [Copyright &y& Elsevier]

Olefin cross metathesis was used to efficiently functionalize polyolefin dendrimers, polymers, and gold nanoparticles using the second-generation Grubbs catalyst. In these structures, the tethers were lengthened to prevent the facile cross metathesis that otherwise predominates in polyolefin dendrimers having short tethers. This synthetic strategy allows the one-step access to polyacid, polyester, and polyferrocenyl structures from polyolefins. Cross metathesis is also used to efficiently achieve an iterative divergent dendritic construction. All the cross metathesis reactions were monitored by ¹H NMR showing the chemio-, regio-, and stereoselectivity. MALDI-TOF mass spectrometry was a very useful technique to confirm the efficiency of this synthetic strategy. [ABSTRACT FROM AUTHOR]