Palladium(0) Nanoparticles on Glass-Polymer Composite Materials as Recyclable Catalysts: A Comparison Study on their Use in Batch and Continuous Flow Processes

Inductive heating and flow chemistry – a perfect synergy of emerging enabling technologies

Inductive heating has developed into a powerful and rapid indirect heating technique used in various fields of chemistry, but also in medicine. Traditionally, inductive heating is used in industry, e.g., for heating large metallic objects including bending, bonding, and welding pipes. In addition, inductive heating has emerged as a partner for flow chemistry, both of which are enabling technologies for organic synthesis. This report reviews the combination of flow chemistry and inductive heating in industrial settings as well as academic research and demonstrates that the two technologies ideally complement each other.

Hollow porous organic nanospheres for anchoring Pd(PPh3)4 through a co-hyper-crosslinking mediated self-assembly strategy

A facile synthesis of Pd(PPh₃)₄-functionalized hollow porous organic nanospheres with excellent catalytic activity is reported for the first time.

Suzuki–Miyaura Coupling Using Monolithic Pd Reactors and Scaling-Up by Series Connection of the Reactors

The space integration of the lithiation of aryl halides, the borylation of aryllithiums, and Suzuki–Miyaura coupling using a Pd catalyst supported by a polymer monolith flow reactor without using an intentionally added base was achieved. To scale up the process, a series connection of the monolith Pd reactor was examined. To suppress the increase in the pressure drop caused by the series connection, a monolith reactor having larger pore sizes was developed by varying the temperature of the monolith preparation. The monolithic Pd reactor having larger pore sizes enabled Suzuki–Miyaura coupling at a higher flow rate because of a lower pressure drop and, therefore, an increase in productivity. The present study indicates that series connection of the reactors with a higher flow rate serves as a good method for increasing the productivity without decreasing the yields.

My Twenty Years in Microwave Chemistry: From Kitchen Ovens to Microwaves that aren't Microwaves

This Personal Account describes the author's involvement in the field of microwave-assisted organic synthesis (MAOS) from the late 1990's starting out with kitchen microwave ovens right through to the development of a reactor in 2016 that - although not using microwave technology - in many ways mimics the performance of a modern laboratory microwave. The reader is taken along a journey that has spanned two decades of intense research on various aspects of microwave chemistry, and, at the same time, was intimately linked to key innovations regarding equipment design and development. A "behind the scenes" approach is taken in this article to share - from a very personal point of view - how specific projects and research ideas were conceived and developed in my research group, and how in general the field of microwave chemistry has progressed in the last two decades.

Continuous-Flow Suzuki-Miyaura and Mizoroki-Heck Reactions under Microwave Heating Conditions

Microwave-assisted continuous-flow reactions have attracted significant interest from synthetic organic chemists, especially process chemists from practical points of view, due to a less complicated shift to large-scale synthesis based on simple and continuous access to products with low energy requirements. In this personal account, we focused on the Suzuki-Miyaura and Mizoroki-Heck reactions, both of which are significantly important cross-coupling reactions for the synthesis of various functional materials. Microwave power is effective for heating. Typical homogeneous palladium catalysts, such as PdCl₂ (PPh₃ )₂ , Pd(PPh₃ )₄ , and Pd(OAc)₂ , as well as heterogeneous palladium catalysts, such as Pd-film, Pd/Al₂ O₃ , Pd/SiO₂ , and Pd supported on polymers, can be used for these reactions.

Ecofriendly Palladium on Wool Nanocatalysts for Cyclohexene Hydrogenation

Use of natural wool fiber supports in the fabrication of novel composite materials incorporating metal nanoparticles, which offer the possibility of “environmentally friendly” catalytic materials, has been investigated. The catalytic hydrogenation of cyclohexene to cyclohexane by palladium nanoparticles immobilized on wool (Pd/wool) was studied using moderate pressure of pure hydrogen gas. The performance of wool-supported catalysts was explored over a palladium nanoparticle loading ranging from 1.6 to 2.6 wt %. The effect of the catalytic testing conditions, including stirring rate, amount of reactants, gas pressure, and target temperature were explored. A systematic series of catalytic-activity tests carried out at 400 psi H₂ for 5 and 24 h reaction times at 40 °C using a stirring rate 750 rpm allowed us to identify differences in performance within the series of Pd/wool nanocatalysts studied. The most catalytically active samples contained Pd nanoparticles with average sizes of ca. 5 nm located predominantly on the surface and within the topmost layer of wool fibers, making them more accessible to the reactants.

Predesigned Metal-Anchored Building Block for In Situ Generation of Pd Nanoparticles in Porous Covalent Organic Framework: Application in Heterogeneous Tandem Catalysis

The development of nanoparticle-polymer-hybrid-based heterogeneous catalysts with high reactivity and good recyclability is highly desired for their applications in the chemical and pharmaceutical industries. Herein, we have developed a novel synthetic strategy by choosing a predesigned metal-anchored building block for in situ generation of metal (Pd) nanoparticles in the stable, porous, and crystalline covalent organic framework (COF), without using conventional reducing agents. In situ generation of Pd nanoparticles in the COF skeleton is explicitly confirmed from PXRD, XPS, TEM images, and ¹⁵N NMR spectral analysis. This hybrid material is found to be an excellent reusable heterogeneous catalyst for the synthesis of biologically and pharmaceutically important 2-substituted benzofurans from 2-bromophenols and terminal alkynes via a tandem process with the turnover number up to 1101. The heterogeneity of the catalytic process is unambiguously verified by a mercury poisoning experiment and leaching test. This hybrid material shows superior catalytic performance compared to commercially available homogeneous as well as heterogeneous Pd catalysts.

Amphipathic monolith-supported palladium catalysts for chemoselective hydrogenation and cross-coupling reactions

Monolithic polymer-supported, effective, and reusable palladium catalysts were developed for cross-coupling reactions and hydrogenation.

Integration of borylation of aryllithiums and Suzuki–Miyaura coupling using monolithic Pd catalyst

Integration of the preparation of arylboronic esters and Suzuki–Miyaura coupling using monolithic Pd catalyst was successfully achieved.

A nitrogen and sulphur functionalized graphene oxide–palladium nanoparticle hybrid catalyst for an efficient Heck coupling

A nanohybrid of Pd on GO functionalized with N and S has been fabricated, and demonstrated as an efficient catalyst for Heck coupling with a substantially low catalytic loading (0.02 mol%).

Nanocatalysis in Flow

Nanocatalysis in flow is catalysis by metallic nanoparticles (NPs; 1-50 nm) performed in microstructured reactors. These catalytic processes make use of the enhanced catalytic activity and selectivity of NPs and fulfill the requirements of green chemistry. Anchoring catalytically active metal NPs within a microfluidic reactor enhances the reagent/catalyst interaction, while avoiding diffusion limitations experienced in classical approaches. Different strategies for supporting NPs are reviewed herein, namely, packed-bed reactors, monolithic flow-through reactors, wall catalysts, and a selection of novel approaches (NPs embedded on nanotubes, nanowires, catalytic membranes, and magnetic NPs). Through a number of catalytic reactions, such as hydrogenations, oxidations, and cross-coupling reactions, the advantages and possible drawbacks of each approach are illustrated.

Palladium salt and functional reduced graphene oxide complex: in situ preparation of a generally applicable catalyst for C–C coupling reactions

A simple scheme of Pd²⁺ fixed on FRGO as a highly efficient coupling catalyst.

A green approach for the decoration of Pd nanoparticles on graphene nanosheets: An in situ process for the reduction of C–C double bonds and a reusable catalyst for the Suzuki cross-coupling reaction

In situ synthesis of Pd nanoparticles on graphene nanosheets with simultaneous reduction of alkene to alkane using hydrogen gas were utilized as efficient catalysts for the Suzuki cross-coupling reaction.

Palladium catalyst supported on PEGylated imidazolium based phosphinite ionic liquid-modified magnetic silica core–shell nanoparticles: a worthy and highly water-dispersible catalyst for organic reactions in water

A highly water-dispersible palladium nanocatalyst was fabricated by the immobilization of Pd onto the surface of PEGylated imidazolium based phosphinite ionic liquid functionalized γ-Fe₂O₃@SiO₂ core–shell nanoparticles.

Palladium-phosphorus/sulfur nanoparticles (NPs) decorated on graphene oxide: synthesis using the same precursor for NPs and catalytic applications in Suzuki-Miyaura coupling

PdP2 and Pd4S nanoparticles (NPs) (size: ∼2-6 and 9-15 nm respectively) have been prepared for the first time from a single source precursor complex [Pd(L)Cl2] (1) by its one pot thermolysis at 200 °C in TOP and OA/ODE (1 : 1) respectively. These NPs were stirred with graphene oxide (GO) at room temperature to prepare NP composites, GO-PdP2 and GO-Pd4S. The GO-PdP2 NPs have been synthesized for the first time. The thioether ligand L prepared by reaction of 1,3-dibromo-2-propanol with the in situ generated PhSNa reacts with [PdCl2(CH3CN)2] in CH3CN at 70 °C resulting in 1. The L and 1 have been characterized by (1)H and (13)C{(1)H} NMR and HR-MS. The single crystal structure of 1 determined by X-ray diffraction reveals nearly square planar geometry around the Pd metal centre. The catalytic activities of two palladium nano-phases having phosphorus and sulphur respectively as a co-constituent for Suzuki-Miyaura coupling have been found to be exceptionally different, as PdP2 nanoparticles (NPs) grafted on graphene oxide (GO-PdP2) are significantly more efficient than Pd4S NPs grafted on GO. Without grafting PdP2 and Pd4S both have low efficiency. This is the first report comparing the influence of P and S on the catalytic activity of Pd NPs. TEM, SEM-EDX and powder-XRD have been used to authenticate all NPs. The GO-PdP2 NPs have been found to be efficient catalysts for Suzuki-Miyaura coupling reactions (yield up to 96% in 30 min) at room temperature to 80 °C. Their recyclability has been found up to 6 cycles. In contrast, GO-Pd4S NPs are little active in comparison with GO-PdP2 NPs. The size of NPs and their distribution on GO appear to be key factors affecting the catalytic efficiency of the composite NPs. Leaching of Pd from GO-PdP2 NPs contributes significantly to the catalysis as evidenced by the three phase test, hot-filtration and recycling experiments. The catalysis is almost homogeneous.

Efficient heterogeneous catalytic hydrogenation of acetone to isopropanol on semihollow and porous palladium nanocatalyst

Highly efficient and remarkable selective acetone conversion to isopropanol has been achieved via a heterogeneous catalytic hydrogenation of acetone by NaBH4 in the presence of semihollow palladium nanoparticles (PdNPs) grown on ITO substrate. PdNPs with high surface defect grown on an indium tin oxide (ITO) surface were prepared via a simple immersion of the substrate into a solution containing K2PdCl6, sodium dodecyl sulphate (SDS), and formic acid for 2 h at room temperature. The sample showed remarkably high heterogeneous catalytic efficiency by producing 99.8% of isopropanol within 6 min using only 0.28 μg of PdNPs on the ITO surface. The present system exhibits heterogenenous catalytic hydrogenation efficiency 1 × 10(6) time higher than using the conventional Raney Ni system.

One-step synthesis of pyridines and dihydropyridines in a continuous flow microwave reactor

The Bohlmann-Rahtz pyridine synthesis and the Hantzsch dihydropyridine synthesis can be carried out in a microwave flow reactor or using a conductive heating flow platform for the continuous processing of material. In the Bohlmann-Rahtz reaction, the use of a Brønsted acid catalyst allows Michael addition and cyclodehydration to be carried out in a single step without isolation of intermediates to give the corresponding trisubstituted pyridine as a single regioisomer in good yield. Furthermore, 3-substituted propargyl aldehydes undergo Hantzsch dihydropyridine synthesis in preference to Bohlmann-Rahtz reaction in a very high yielding process that is readily transferred to continuous flow processing.

Selective hydrogenation over Pd nanoparticles supported on a pore-flow-through silica monolith microreactor with hierarchical porosity

Well-dispersed Pd nanoparticles have been synthesized inside the mesoporosity of a silica monolith featuring hierarchical porosity of homogeneous interconnected macropores (4 microns) and mesopores (11 nm). These monoliths have been implemented as microreactors for selective hydrogenation reactions. Conversion and selectivity can be tuned by adjusting the flow rates of hydrogen and substrates. In the selective hydrogenation of cyclooctadiene, a conversion of 95% and a selectivity of 90% in the monohydrogenated product, constant over a period of 70 h, have been reached. These figures correspond to a productivity of 4.2 mmol s(-1) g(-1)(MonoSil) (or 0.32 mol s(-1) g(-1)(Pd)). In the stereoselective hydrogenation of 3-hexyn-1-ol a constant conversion of 85% was observed, with however moderate selectivity into the cis isomer, over a test period of 7 h. These results open the route to the synthesis of important chemicals and intermediates via safe and green processes.

Suzuki Polycondensation: Polyarylenes à la Carte

This review draws a rather comprehensive picture of how Suzuki polycondensation was discovered in 1989 and how it was subsequently developed into the most powerful polymerization method for polyarylenes during the last 20 years. It combines insights into synthetic issues with classes of polymers prepared and touches upon aspects of this method's technological importance. Because a significant part of the developmental work was carried out in industry, the present review makes reference to an unusually large number of patents.

Scaling up of continuous-flow, microwave-assisted, organic reactions by varying the size of Pd-functionalized catalytic monoliths

A product-scalable, catalytically mediated flow system has been developed to perform Suzuki-Miyaura reactions under a microwave heating regime, in which the volumetric throughput of a Pd-supported silica monolith can be used to increase the quantity of the product without changing the optimal operating conditions. Two silica monoliths (both 3 cm long), with comparable pore diameters and surface areas, were fabricated with diameters of 3.2 and 6.4 mm to give volumetric capacities of 0.205 and 0.790 mL, respectively. The two monoliths were functionalized with a loading of 4.5 wt % Pd and then sealed in heat-shrinkable Teflon(®) tubing to form a monolithic flow reactor. The Pd-supported silica monolith flow reactor was then placed into the microwave cavity and connected to an HPLC pump and a backpressure regulator to minimize the formation of gas bubbles. The flow rate and microwave power were varied to optimize the reactant contact time and temperature, respectively. Under optimal reaction conditions the quantity of product could be increased from 31 mg per hour to 340 mg per hour simply by changing the volumetric capacity of the monolith.

Continuous flow hydrogenation using polysilane-supported palladium/alumina hybrid catalysts

Continuous flow systems for hydrogenation using polysilane-supported palladium/alumina (Pd/(PSi-Al(2)O(3))) hybrid catalysts were developed. Our original Pd/(PSi-Al(2)O(3)) catalysts were used successfully in these systems and the hydrogenation of unsaturated C-C bonds and a nitro group, deprotection of a carbobenzyloxy (Cbz) group, and a dehalogenation reaction proceeded smoothly. The catalyst retained high activity for at least 8 h under neat conditions.