Go Hamasaka

Highly efficient iron(0) nanoparticle-catalyzed hydrogenation in water in flow

Highly efficient catalytic hydrogenations are achieved by using amphiphilic polymer-stabilized Fe(0) nanoparticle (Fe NP) catalysts in ethanol or water in a flow reactor. Alkenes, alkynes, aromatic imines and aldehydes were hydrogenated nearly quantitatively in most cases. Aliphatic amines and aldehydes, ketone, ester, arene, nitro, and aryl halide functionalities are not affected, which provides an interesting chemoselectivity. The Fe NPs used in this system are stabilized and protected by an amphiphilic polymer resin, providing a unique system that combines long-term stability and high activity. The NPs were characterized by TEM of microtomed resin, which established that iron remains in the zero-valent form despite exposure to water and oxygen. The amphiphilic resin-supported Fe(0) nanoparticles in water and in flow provide a novel, robust, cheap and environmentally benign catalyst system for chemoselective hydrogenations.

Molecular‐Architecture‐Based Administration of Catalysis in Water: Self‐Assembly of an Amphiphilic Palladium Pincer Complex

Biological membranes are known to play a key role in controlling life-related molecular functions (e.g., active/ passive transport, diffusion, filtration, selective permeation, etc.). Lipid bilayer membrane vesicles (i.e., liposomes) are small assemblies of amphiphilic molecules bearing both hydrophilic and hydrophobic groups and they offer promising prospects for the understanding of biological membranes. If less-catalytically active small molecules can self-assemble to form bilayer vesicles and, in so doing, gain unique catalytic functions for a given molecular transformation, this process could conceivably be used in a catalysis-driven system. We report herein the formation of a bilayer membrane vesicle from an amphiphilic palladium complex through self-assembly to realize palladium-catalyzed carbon–carbon bondforming reactions under ambient conditions (in water, under air, at room temperature), wherein the vesicle architecture is essential for the catalysis. The formation of a catalytically active vesicle and the vesicle-catalyzed organic transformations were both promoted in water by the hydrophobic properties of the substrates and catalysts, as opposed to conventional artificial organic chemical reaction systems (i.e., standard flask reactions) that are often promoted with external driving forces (e.g., heat, pressure, light, etc.). The pincer palladium complex 1 5] having pairs of hydrophobic dodecyl chains and hydrophilic tri(ethylene glycol) (TEG) chains located opposite to one another on the rigid planar backbone, was designed and prepared for use in the self-assembly formation of vesicles exhibiting catalytic activity in water (Scheme 1; see the Supporting Information). After the complex 1, which was obtained as an amorphous nanopowder (1amps; Figure 1a), was treated in water at 60 8C for 4 hours, the resulting aqueous mixture was cooled and subjected to a dynamic light scattering (DLS) study (Figure 1c) to demonstrate the formation of the vesicle 1vscl (average diameter = 550 nm). [7] Vesicle 1vscl was isolated by centrifugation and decantation in 10–40% yield based on the recovery of 1 as an amorphous powder from the supernatant. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) images of the isolated vesicle 1vscl are shown in Figures 1b and d, respectively. These microscopic studies revealed that 1vscl was obtained as hard vesicles. Their spherical form was confirmed by AFM (Figure 1d), and the thickness of the vesicle membrane was determined to be 6 nm by TEM methods (Figure 1b). These data are consistent with those of the bilayer membranous structure of 1mono having a monomer length of approximately 2.8 nm in the structure (Scheme 1). The incorporation of the fluorescent reagent, fluorescein, into the 1vscl revealed a hollow structure with an inner hydrophobic region in the exterior membrane. Thus, when the isolated 1vscl was exposed to fluorescein under aqueous conditions, the fluorescent vesicles, 1vscl/fluorescein, were isolated after rinsing with water. The fluorescence microscopic image and the Scheme 1. Formation of vesicle 1vscl by self-assembly of the pincer palladium complex 1.

A Recyclable “Boomerang” Linear Polystyrene-Stabilized Pd Nanoparticles for the Suzuki Coupling Reaction of Aryl Chlorides in Water

A polymer-supported “boomerang” catalyst that operates through the reversible release of homogeneous catalyst into the solution phase from the polymer support has the advantages of both homogeneous (high activity) and heterogeneous (recovery and recyclability) catalysts. For example, Reiser et al. developed a method for the reversible immobilization of pyrene-tagged palladium–N-heterocyclic carbene complexes on highly magnetic, graphene-coated cobalt nanoparticles (NPs) through p–p stacking interactions. In contrast, metal NPs as catalysts have attracted attention because they possess high catalytic activity in water. Metal NPs have been used not only as a semi-heterogeneous catalyst but also as a semi-heterogeneous support. However, the heterogenization of metal NPs decreased catalytic activity. In addition, the recovery and reuse of metal NPs has been difficult to achieve because of a significant loss and/or morphology change of the metal NPs during the reaction and workup. Because leaching of soluble metal species from the support is a major cause of catalyst deactivation, efforts have been made to develop an effective support that prevents leaching of metal species. In contrast, leaching of palladium species has been observed directly, which showed high catalytic activity in some systems. Palladium NPs generated in situ for the Suzuki coupling reaction and aerobic alcohol oxidation in water were recovered with linear polystyrene, even in the presence of organic compounds. These reports prompted efforts to find recyclable “boomerang” NPs that can overcome the aforementioned problems. This communication describes the development of a catch–release system for soluble palladium species in water with linear polystyrene as an efficient reservoir. Linear polystyrene-stabilized PdO NPs (PS-PdONPs) were prepared through the thermal decomposition of Pd(OAc)2 in the presence of polystyrene, as described previously. The composition (PdO) and size (2.6 0.3 nm) of the NPs were observed by using XRD and TEM, respectively (Figures S1 and S2). The loading value of palladium (2.5 mmol g ) was confirmed by inductively coupled plasma-atomic emission spectrometry (ICPAES) analysis. The SEM image showed that PS-PdONPs possessed a particle aggregate-like structure (Figure S3). According to the nitrogen adsorption analysis, the BET surface area of PSPdONPs was 27.3 m g 1 after vacuum pretreatment at 100 8C. PS-PdONPs had an irregular hollow shape, with a hollow size distribution centered at 2.7, 8.6, and 10.6 nm (Figures S4 and S5). In the Suzuki coupling reaction of aryl bromides with arylboronic acids in the presence of PS-PdONPs, no leaching of palladium into the reaction solution occurred after the reaction, as confirmed by ICP-AES analysis. No increase in the yield of coupling product was observed in the hot filtration test. In addition, the TEM image of the recovered catalyst showed that the size of the NPs was maintained even after the tenth run. With these results in mind, we checked leaching of palladium after the exposure of PS-PdONPs to different reagents in 1.5 mol L 1 of aqueous KOH solution at 80 8C for 1 h (Table 1). No detectable levels of palladium (<0.1 ppm) were observed in the absence of reagent (entry 1) or in the presence of 4-methylphenylboronic acid (entry 2). However, 19 % of palladium leached into the aqueous solution when the mixture of PS-PdONPs and bromobenzene was heated in 1.5 mol L 1 of aqueous KOH solution at 80 8C for 1 h (entry 3). These results indicated that a recyclable homogeneous/heterogeneous catalytic system could be constructed with PS-PdONPs and aryl halide.

Hydrogenation of Hindered Ketones Catalyzed by a Silica-Supported Compact Phosphine−Rh System

A heterogeneous mono(phosphine)-Rh catalyst system silica-SMAP-Rh(OMe)(cod), where silica-SMAP stands for a caged, compact trialkylphosphine (SMAP) supported on silica gel, showed broad applicability toward the hydrogenation of hindered ketones. Doubly alpha-branched ketones such as diisopropyl ketone was hydrogenated under nearly atmospheric conditions. Di-tert-butyl ketone could be hydrogenated under more forcing conditions.

Detailed Structural Analysis of a Self-Assembled Vesicular Amphiphilic NCN-Pincer Palladium Complex by Using Wide-Angle X-Ray Scattering and Molecular Dynamics Calculations.

Wide-angle X-ray scattering experiments and all-atomistic molecular dynamics calculations were performed to elucidate the detailed structure of bilayer vesicles constructed by self-assembly of an amphiphilic palladium NCN-pincer complex. We found an excellent agreement between the experimental and calculated X-ray spectra, and between the membrane thickness determined from a TEM image and that calculated from an electron-density profile, which indicated that the calculated structure was highly reliable. The analysis of the simulated bilayer structure showed that in general the membrane was softer than other phospholipid bilayer membranes. In this bilayer assemblage, the degree of alignment of complex molecules in the bilayer membrane was quite low. An analysis of the electron-density profile shows that the bilayer assemblage contains a space through which organic molecules can exit. Furthermore, the catalytically active center is near this space and is easily accessible by organic molecules, which permits the bilayer membrane to act as a nanoreactor. The free energy of permeation of water through the bilayer membrane of the amphiphilic complex was 12 kJ mol-1 , which is much lower than that for phospholipid bilayer membranes in general. Organic molecules are expected to pass though the bilayer membrane. The self-assembled vesicles were shown to be catalytically active in a Miyaura-Michael reaction in water.

Ligand-Introduction Synthesis of NCN-Pincer Complexes and their Chemical Properties

Abstract In this chapter, we describe the synthesis by the ligand-introduction route of a wide range of palladium NCN-pincer complexes, including N-alkylimino and N-arylimino palladium NCN-pincer complexes, palladium NCN-pincer complexes bearing chiral pyrroloimidazolone groups, and [2,6-bis(2-oxazolinyl)phenyl] palladium complexes. We also describe some applications of these ligands. The prepared NCN-pincer complexes show good catalytic performances in asymmetric Michael reactions and Mizoroki-Heck reactions. A palladium NCN-imino pincer complex has also been used as a probe molecule to index the coordination ability of various monodentate ligands. Amphiphilic palladium N-arylimino pincer complexes are capable of self-assembly to form vesicular architectures that act as good catalysts for organic reactions in water. The ligand-introduction route deserves to be recognized as an alternative synthetic route for the synthesis of pincer complexes.

Spirocyclization of Alkyne-Tethered Aromatics with Silver Nitrate/Silica

Significance: Silica-supported silver nitrate (AgNO3/SiO2) catalyzed the dearomatizing spirocyclization of alkyne-tethered aromatics to give the corresponding spirocycles in 86–100% yield (eqs. 1–4). Comment: The continuous-flow reaction of 1(1H-indol-3-yl)-4-phenylbut-3-yn-2-one on a column of AgNO3/SiO2 gave 5-phenyl-3H-spiro[cyclopent-4-ene-1,3′-indol]-3-one in quantitative yield (eq. 5). AgNO3/SiO2 (1 mol% Ag) CH2Cl2, r.t. to 45 °C 10 min to 24 h (1)

Graphene Oxide Promoted C–H Arylation of Benzene with Aryl Halides

533 Y . G A O, P . TA NG , H . Z H O U , W. Z H A N G , H . YA N G, N . YA N , G . H U, D . M E I , J . WA NG , * D . M A * ( P E K I N G U N I V E R S I T Y, B E I J I N G, Z HE JI A N G U NI VE R S I T Y O F TE C H N O L OG Y, HA N G Z H O U , I S R A E L C H E M I C A L S L T D . , S H AN G H A I , P. R . O F C HI NA ; N A T I O N A L U NI V E R S I T Y O F SINGAPORE, SINGAPORE; AND PACIFIC NORTHWEST NATIONAL LABORATORY, RICHLAND, U S A) Graphene Oxide Catalyzed C–H Bond Activation: The Importance of Oxygen Functional Groups for Biaryl Construction Angew. Chem. Int. Ed. 2016, 55, 3124–3128.

Asymmetric Michael and Aldol Reactions with a Supported Chiral Diamine

1097 A . YI N G, * S . L I U , Z . L I , G . CH E N , J . YA N G , H . YA N , S . XU * ( TA I Z H O U U N I V E R S I T Y, N A N K A I U N I V E R S I T Y, TI A N JI N , A N D TI A N JI N U N I V E R SI T Y, P. R . O F C H I N A) Magnetic Nanoparticles-Supported Chiral Catalyst with an Imidazolium Ionic Moiety: An Efficient and Recyclable Catalyst for Asymmetric Michael and Aldol Reactions Adv. Synth. Catal. 2016, 358, 2116–2125.

C–H Borylation of Cyclopropanes and Cyclobutanes with Silica-SMAP–Iridium

Significance: The heteroatom-directed C–H borylation of cyclopropanes and cyclobutanes with bis(pinacolato)diboron was carried out in the presence of [Ir(OMe)(cod)]2 and silica-SMAP to give the corresponding borylated products in up to 168% yield based on bis(pinacolato)diboron (eqs. 1 and 2). Comment: In the reaction of 2-cyclopropylpyridine with bis(pinacolato)diboron, the catalytic activity of the silica-SMAP–iridium system was superior to that of the other ligand–iridium systems (for example, 0% yield for Ph-SMAP–Ir, Me3P–Ir, t-Bu3P–Ir, Ph3P–Ir, XPhos–Ir, dtbpy–Ir, and 2,9-Me2Phen–Ir). Si P