Palladium Nanoparticles Bonded to Two-Dimensional Iron Oxide Graphene Nanosheets: A Synergistic and Highly Reusable Catalyst for the Tsuji-Trost Reaction in Water and Air

Green protocols for Tsuji–Trost allylation: an overview

Since its inception in 1960s, the Tsuji–Trost reaction, an allylic substitution reaction with diverse nucleophiles such as phenols, amines, thiols, and active methylene compounds, has remained as one of the most useful and widely used organic reactions for the construction of C–C and C–heteroatom bonds. Allylic compounds such as allylic acetates, alcohols, halides, and carbonates undergo this transformation which plays an important role in the total synthesis of various natural products. The competence to incorporate synthetically demanding allylic functionalities makes it a beneficial tool for the synthesis of complex molecules. Over the last two decades, major advancements for this unique and facile Tsuji–Trost allylation reaction have been made with special emphasis to develop greener and sustainable protocols. This chapter presents an update on the significant progress focusing on the newly designed catalytic systems with high efficiency, the use of eco-friendly solvents or solvent-free conditions, low or room temperature conditions and waste management, along with future outlook.

Chitosan as capping agent in a robust one-pot procedure for a magnetic catalyst synthesis

Here, we report a one-pot solvothermal method for the development of magnetically recoverable catalysts with Ru or Ag nanoparticles (NPs) capped by chitosan (CS), a derivative of natural chitin. The formation of iron oxide NPs was carried out in situ in the presence of CS and iron acetylacetonate in boiling triethyleneglycol (TEG) due to CS solubilization in warm TEG. Coordination with Ru or Ag species and the NP formation take place in the same reaction solution, eliminating intermediate steps. In optimal conditions the method developed allows stabilization of 2.2 nm monodisperse Ru NPs (containing both Ru⁰ and Ru⁴⁺ species) that are evenly distributed through the catalyst, while for Ag NPs, this stabilizing medium is inferior, leading to exceptionally large Ag nanocrystals. Catalytic testing of CS-Ru magnetically recoverable catalysts in the reduction of 4-nitrophenol to 4-aminophenol with excess NaBH₄ revealed that the catalyst with 2.2 nm Ru NPs exhibits the highest catalytic activity compared to samples with larger Ru NPs (2.9-3.2 nm). Moreover, this catalyst displayed extraordinary shelf-life in the aqueous solution (up to ten months) and excellent reusability in ten consecutive reactions with easy magnetic separation at each step which were assigned to its conformational rigidity at a constant pH. These characteristics as well as favorable environmental factors of the catalyst fabrication, make it promising for nitroarene reduction.

Dehydrogenative Coupling of Alkanes and Benzene Enhanced by Slurry-Phase Interparticle Hydrogen Transfer

The dehydrogenative coupling reaction of alkanes and benzene has attracted attention as a method of direct conversion of alkanes to raw materials for useful chemical products. Here, we report the first combined catalyst system composed of hydrotalcite-supported palladium and solid acid aluminum-exchanged montmorillonite for the direct alkylation of benzene promoted by slurry-phase interparticle hydrogen transfer at 150 °C. The combination of the two catalytic particles showed excellent activity and achieved the maximum benzene conversion of 21% and target product selectivity of 84% in the reaction of n-heptane and benzene. Our results, thus, provide a feasible strategy to design efficient liquid-phase reaction systems employing simple physical mixing of two catalytic particles.

Nano-catalytic behavior of highly efficient and regenerable mussel-inspired Fe3O4@CFR@GO and Fe3O4@CFR@TiO2 magnetic nanospheres in the reduction of Evans blue dye

Fe₃O₄@catechol formaldehyde resin coated @Graphene Oxide nanocomposite (Fe₃O₄@CFR@GO) and Fe₃O₄@catechol formaldehyde resin coated @TiO₂ (Fe₃O₄@CFR@TiO₂) nanocomposite were fabricated by hydrothermal method. Particularly, catechol bunches on the highest layer of nanospheres to play a mussel-inspired chemistry to assist combined with graphene oxide (GO) to wrap the Fe₃O₄@ coated nanosphere. The prepared catalyst was proven to be very efficient with less than a minute and vey less dosage (15–17 mg) in the adsorptive degradation of Evans blue dye. The adsorptive degradation of Evans blue dye with Fe₃O₄@CFR@GO and Fe₃O₄@CFR@TiO₂ nanocomposites are studied by several variables like the dye concentration, dosage, pH, contact time and temperature. It shows maximum adsorption capacity of 0.1435 mg/g (Fe₃O₄@CFR@GO) and 9.345 mg/g (Fe₃O₄@CFR@TiO₂) nanocomposites. The equilibrium concentration and the adsorption capacity were evaluated using three different isothermal models. The kinetic study determined that Evans blue dye adsorption was in good analogy with the pseudo-first-order kinetic model.

Heterogeneous Supported Palladium Catalysts for Liquid-Phase Allylation of Nucleophiles

In recent years, palladium-catalyzed allylation has become the focus of much research. However, conventional homogeneous Pd catalysts face problems regarding their recovery, reuse, and cost, especially with respect to green chemistry principles. Herein, we present an overview of the development of catalytic allylation with various heterogeneous Pd catalysts, because they can be easily and conveniently recovered and reused. We also emphasize the use of different solid supports such as polymers, silica, and other hybrid supports to inspire future research in this promising field. Moreover, the unique effects of support surfaces for enhancing catalysis by immobilized heterogeneous Pd species are introduced.

Multifunctional Catalytic Surface Design for Concerted Acceleration of One-Pot Hydrosilylation-CO2 Cycloaddition

Silica-supported Rh-ammonium iodide catalyst showed high performance for hydrosilylation-CO₂ cycloaddition reaction sequences. The catalyst was prepared by surface grafting of Rh and the silane-coupling reaction of the ammonium iodide moiety. The acceleration of each catalytic reaction was realized due to the concerted catalysis between Rh species, immobilized organic functions, and surface Si-OH groups. As a result, good to excellent yields of silyl carbonates were obtained from epoxyolefins, hydrosilanes, and CO₂ under mild reaction conditions.

Quaternized POSS modified rGO-supported Pd nanoparticles as a highly efficient catalyst for reduction and Suzuki coupling reactions

Hydrophilic QPOSS modified rGO nanosheets are fabricated as a robust catalyst support of PdNPs for reduction and Suzuki coupling reactions.

Mussel-Inspired Catechol-Formaldehyde Resin-Coated Fe3O4 Core-Shell Magnetic Nanospheres: An Effective Catalyst Support for Highly Active Palladium Nanoparticles

Magnetic Fe₃O₄@catechol-formaldehyde resin (CFR) core-shell nanospheres were fabricated via a controllable hydrothermal method. The shell thickness of Fe₃O₄@CFR nanospheres can be effectively regulated in the range of 10-170 nm via adjusting reaction parameters. In particular, catechol groups on the surface of nanospheres also play a significant role in mussel-inspired chemistry to further combine with graphene oxide (GO) to wrap the Fe₃O₄@CFR spheres. The obtained Fe₃O₄@CFR and Fe₃O₄@CFR@GO nanospheres can be used as the effective catalyst supports of small Pd nanoparticles (PdNPs, <10 nm) formed via an in situ synthesis route. The as-fabricated nanohybrid catalysts of Fe₃O₄@CFR@PdNPs and Fe₃O₄@CFR@GO@PdNPs with excellent dispersibility and stability are reusable after magnetic separation from catalytic systems. In particular, a super active performance was demonstrated for the catalytic reduction of methylene blue dye with highest turnover frequency (5260 min^-1) yet reported in the literature using a very low dosage of the Fe₃O₄@CFR@GO@PdNP catalyst. In addition, the Fe₃O₄@CFR@GO@PdNP catalyst also exhibits a highly catalytic efficiency for the Suzuki coupling reaction using pure water as a green solvent at room temperature.

Facile Synthesis of Magnetically Recoverable Pd and Ru Catalysts for 4-Nitrophenol Reduction: Identifying Key Factors

This paper reports the development of robust Pd- and Ru-containing magnetically recoverable catalysts in a one-pot procedure using commercially available, branched polyethyleneimine (PEI) as capping and reducing agent. For both catalytic metals, ∼3 nm nanoparticles (NPs) are stabilized in the PEI shell of magnetite NPs, whose aggregation allows for prompt magnetic separation. The catalyst properties were studied in a model reaction of 4-nitrophenol hydrogenation to 4-aminophenol with NaBH4. A similar catalytic NP size allowed us to decouple the NP size impact on the catalytic performance from other parameters and to follow the influence of the catalytic metal type and amount as well as the PEI amount on the catalytic activity. The best catalytic performances, the 1.2 min-1 rate constant and the 433.2 min-1 turnover frequency, are obtained for the Ru-containing catalyst. This is discussed in terms of stability of Ru hydride facilitating the surface-hydrogen transfer and the presence of Ru4+ species on the Ru NP surface facilitating the nitro group adsorption, both leading to an increased catalyst efficiency. High catalytic activity as well as the high stability of the catalyst performance in five consecutive catalytic cycles after magnetic separation makes this catalyst promising for nitroarene hydrogenation reactions.

Mussel-inspired construction of thermo-responsive double-hydrophilic diblock copolymers-decorated reduced graphene oxide as effective catalyst supports for highly dispersed superfine Pd nanoparticles

Well-dispersed ultrafine palladium nanoparticles supported by reduced graphene oxide functionalized with catechol-terminated thermo-responsive block copolymer (PdNPs@BPrGO) were successfully constructed for highly efficient heterogeneous catalytic reduction. We first synthesized a novel temperature-responsive episulfide-containing double-hydrophilic diblock copolymer, poly(poly(ethylene glycol) methyl ether methacrylate-co-2,3-epithiopropyl methacrylate)-block-poly(N-isopropylacrylamide) (P(PEGMA-co-ETMA)-b-PNIPAM), through a reversible addition-fragmentation chain transfer (RAFT) polymerization utilizing a chain-transfer agent with a catechol unit as the end group. The obtained block copolymers can be facilely anchored to the surface of GO via mussel-inspired chemistry. The PdNPs were loaded on GO decorated with block copolymer brushes (BPrGO) as a support via the in situ reduction of palladium precursors with the episulfide ligands of the block copolymer as a stabilizer. The resulting PdNPs@BPrGO nanohybrid catalyst had good water dispersibility and stability. Furthermore, a low dosage of PdNPs@BPrGO catalyst exhibited excellent catalytic performance in the reduction of methylene blue and nitrophenols. The performance was attributed to the ability of PdNPs@BPrGO to facilitate the diffusion of reactants compared to PdNPs@GO without polymer modification. PdNPs@BPrGO also possessed an interesting temperature-responsive catalytic property due to the reversible "coil-to-globule" phase transition behaviour of PNIPAM blocks onto the surface of catalyst. The PdNPs@BPrGO catalyst was successfully recovered and reused five times without any detectible loss in catalytic activity, demonstrating its great potential in a wide range of industrial catalytic applications.

Facile Fabrication of Highly Active Magnetic Aminoclay Supported Palladium Nanoparticles for the Room Temperature Catalytic Reduction of Nitrophenol and Nitroanilines

Magnetically recyclable nanocatalysts with excellent performance are urgent need in heterogeneous catalysis, due to their magnetic nature, which allows for convenient and efficient separation with the help of an external magnetic field. In this research, we developed a simple and rapid method to fabricate a magnetic aminoclay (AC) based an AC@Fe₃O₄@Pd nanocatalyst by depositing palladium nanoparticles (Pd NPs) on the surface of the magnetic aminoclay nanocomposite. The microstructure and the magnetic properties of as-prepared AC@Fe₃O₄@Pd were tested using transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and vibrating sample magnetometry (VSM) analyses. The resultant AC@Fe₃O₄@Pd nanocatalyst with the magnetic Fe-based inner shell, catalytically activate the outer noble metal shell, which when combined with ultrafine Pd NPs, synergistically enhanced the catalytic activity and recyclability in organocatalysis. As the aminoclay displayed good water dispersibility, the nanocatalyst indicated satisfactory catalytic performance in the reaction of reducing nitrophenol and nitroanilines to the corresponding aminobenzene derivatives. Meanwhile, the AC@Fe₃O₄@Pd nanocatalyst exhibited excellent reusability, while still maintaining good activity after several catalytic cycles.

Highly efficient Tsuji–Trost allylation in water catalyzed by Pd-nanoparticles

Palladium nanoparticles stabilized by poly(vinylpyrrolidone) catalyze Tsuji–Trost allylations in water with very high turnover numbers.

Direct Estimation of the Surface Location of Immobilized Functional Groups for Concerted Catalysis Using a Probe Molecule

The location of active sites during concerted catalysis by a metal complex and tertiary amine on a SiO2 surface is discussed based on the interaction between the functionalized SiO2 surface and a probe molecule, p-formyl phenylboronic acid. The interactions of the probe molecule with the surface functionalities, diamine ligand, and tertiary amine, were analyzed by FT-IR and solid-state (13)C and (11)B MAS NMR. For the catalyst exhibiting high 1,4-addition activity, the diamine ligand and tertiary amine base exist in closer proximity than in the catalyst with low activity.

Rational synthesis of Pd nanoparticle-embedded reduced graphene oxide frameworks with enhanced selective catalysis in water

A three-dimensional (3D) Pd-reduced graphene oxide framework (Pd-rGOF) with hierarchical macro- and mesoporous structures has been developed via covalence- and coordination-assisted self-assembly approach. In this facile fabrication process, GO was first cross-linked with triethylene tetramine (TETA) to form 3D GOF, in which well-dispersed and ultrasmall Pd nanoparticles (NPs) in situ grew and embedded the framework. The obtained nanopores, 3D Pd-rGOF, can act as nanoreactors to help the reaction substrates thoroughly contact with the surface of Pd NPs, thereby exhibiting high activity and selectivity toward the Tsuji-Trost reaction in water, with 99% conversion and selectivity for most substrates. Moreover, the 3D Pd-rGOF catalyst can be reused more than ten times without significant loss of activity, rendering this catalyst long-term stability. The abovementioned observations make the rGOF a universal platform to coordinate other noble metal ions (NM) to construct desired NM-rGOF nanocatalysts with improved activity, selectivity, and durability that can be used in a broad range of practical applications.

Metal-supported carbon-based materials: opportunities and challenges in the synthesis of valuable products

We summarize relevant applications and limitations of metal-supported carbons and nanocarbons in the synthesis of valuable products and the recent advances in this field.

Green synthesis and characterization of gold nanoparticles embedded into magnetic carbon nanocages and their highly efficient degradation of methylene blue

We reported the Au NPs/MCNSs nanohybrids as the catalysts for the highly efficient and selective degradation of methylene blue.

1,4-Dihydroxyanthraquinone–copper(ii) supported on superparamagnetic Fe3O4@SiO2: an efficient catalyst for N-arylation of nitrogen heterocycles and alkylamines with aryl halides and click synthesis of 1-aryl-1,2,3-triazole derivatives

1,4-Dihydroxyanthraquinone–copper(ii) supported on superparamagnetic Fe₃O₄@SiO₂ catalyst was employed for the N-arylation of nitrogen heterocycles and alkylamines.

A strongly coupled Au/Fe3O4/GO hybrid material with enhanced nanozyme activity for highly sensitive colorimetric detection, and rapid and efficient removal of Hg(2+) in aqueous solutions

We have developed an efficient strategy for synthesizing a strongly coupled Au/Fe3O4/GO hybrid material to improve the catalytic activity, stability, and separation capability of Au nanoparticles (NPs) and Hg(2+). The hybrid material can be synthesized by the direct anchoring of Au and Fe3O4 NPs on the functional groups of GO. This approach affords strong chemical attachments between the NPs and GO, allowing this hybrid material to ultrasensitively detect Hg(2+) in aqueous solutions with a detection limit as low as 0.15 nM. In addition, the deposition of Hg(0) on the surface of Au/Fe3O4/GO could be quickly (within 30 min) and efficiently (>99% elimination efficiency) removed by the simple application of an external magnetic field and then Au/Fe3O4/GO could be subsequently reused at least 15 times, with the elimination efficiency remaining high (>96%).

Heterogeneous double-activation catalysis: Rh complex and tertiary amine on the same solid surface for the 1,4-addition reaction of aryl- and alkylboronic acids

Double-activation catalysis by a rhodium complex/tertiary amine catalyst for the 1,4-addition of organoboronic acids was investigated.

Highly efficient degradation of organic dyes by palladium nanoparticles decorated on 2D magnetic reduced graphene oxide nanosheets

We report a novel and effective strategy to synthesize Pd/Fe₃O₄-PEI-RGO nanohybrids for highly efficient degradation of organic dyes.

Size- and shape-dependent peroxidase-like catalytic activity of MnFe2O4 Nanoparticles and their applications in highly efficient colorimetric detection of target cancer cells

FA- and FITC-labeled MnFe₂O₄ nanohybrid exhibits highly efficient colorimetric detection of target cancer cells.