Atsushi Ohtaka

Synthesis and characterization of polypyrrole-palladium nanocomposite-coated latex particles and their use as a catalyst for Suzuki coupling reaction in aqueous media.

Polypyrrole-palladium (PPy-Pd) nanocomposite was deposited in situ from aqueous solution onto micrometer-sized polystyrene (PS) latex particles. The PS seed particles and resulting composite particles were extensively characterized with respect to particle size and size distribution, morphology, surface/bulk chemical compositions, and conductivity. PPy-Pd nanocomposite loading onto the PS seed latex particles was systematically controlled over a wide range (10-60 wt %) by changing the weight ratio of the PS latex and PPy-Pd nanocomposite. Pd loading was also controlled between 6 and 33 wt %. The conductivity of pressed pellets increased with the PPy-Pd nanocomposite loading and four-point probe measurements indicated conductivities ranging from 3.0 x 10(-1) to 7.9 x 10(-6) S cm(-1). Hollow capsule and broken egg-shell morphologies were observed by scanning/transmission electron microscopy after extraction of the PS component from the composite particles, which confirmed a PS core and PPy-Pd nanocomposite shell morphology. X-ray diffraction confirmed that the production of elemental Pd and X-ray photoelectron spectroscopy indicated the existence of elemental Pd on the surface of the composite particles. Transmission electron microscopy confirmed that nanometer-sized Pd particles were distributed in the shell. The nanocomposite particles functioned as an efficient catalyst for Suzuki-type coupling reactions in aqueous media for the formation of carbon-carbon bonds.

Linear polystyrene-stabilized palladium nanoparticles-catalyzed C-C coupling reaction in water.

Linear polystyrene-stabilized PdO nanoparticles (PS-PdONPs) were prepared in water by thermal decomposition of Pd(OAc)(2) in the presence of polystyrene. The immobilization degree of palladium was dependent on the molecular weight of polystyrene, while the size of the Pd nanoparticles was not. Linear polystyrene-stabilized Pd nanoparticles (PS-PdNPs) were also prepared using NaBH(4) and phenylboronic acid as reductants. The catalytic activity of PS-PdONPs was slightly higher than that of PS-PdNPs for Suzuki coupling reaction in water. PS-PdONPs exhibited high catalytic activity for Suzuki and copper-free Sonogashira coupling reactions in water and recycled without loss of activity.

Facile preparation of linear polystyrene-stabilized Pd nanoparticles in water

Palladium nanoparticles can be readily stabilized onto linear polystyrene by a simple procedure. The resultant polystyrene-stabilized Pd has high catalytic activity for Suzuki-Miyaura cross-coupling reaction in water and can be reused without loss of activity.

Recyclable Polymer-Supported Nanometal Catalysts in Water

Two types of polymer-supported nanometal catalysts with high catalytic activity and recyclability in water have been developed. One catalyst was composed of linear polystyrene-stabilized metal nanoparticles (PS-MtNPs). A palladium catalyst (PS-PdONPs) was prepared in water by the thermal decomposition of Pd(OAc)2 in the presence of polystyrene. The degree of immobilization of Pd, but not the size of the Pd nanoparticles, was dependent on the molecular weight and cross-linking of the polystyrene. The PS-PdONPs exhibited high catalytic activity for Suzuki, Heck, and Sonogashira coupling reactions in water and they could be recycled without loss of activity. Linear polystyrene was also suitable as a stabilizer for in situ generated PdNPs and PtNPs. The second catalyst was a polyion complex that was composed of poly[4-chloromethylstyrene-co-(4-vinylbenzyl)tributylammonium chloride] and poly(acrylic acid)-stabilized PdNPs (PIC-PdNPs). Aggregation and redispersion of PIC-PdNPs were easily controlled by adjusting the pH value of the solution.

Linear polystyrene-stabilized PdO nanoparticle-catalyzed Mizoroki-Heck reactions in water.

Linear polystyrene-stabilized PdO nanoparticles (PS-PdONPs) were prepared by thermal decomposition of Pd(OAc)2 in the presence of polystyrene. X-ray diffraction (XRD) and transmission electron microscopy (TEM) indicated the production of PdO nanoparticles. The loading of palladium was determined by inductively coupled plasma-atomic emission spectroscopy (ICP-AES). PS-PdONPs exhibited high catalytic activity for Mizoroki-Heck reactions under air in water and could be recycled without loss of activity.

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.

One-step synthesis of magnetic iron–conducting polymer–palladium ternary nanocomposite microspheres with applications as a recyclable catalyst

Magnetic iron–conducting polymer–palladium ternary nanocomposite microspheres were synthesized in a one-pot, single step process via aqueous chemical oxidative polymerization. These microspheres functioned as an efficient catalyst for the Suzuki–Miyaura cross-coupling reaction and can be readily recycled using only a magnetic field.

Conducting Polymer-Metal Nanocomposite Coating on Fibers

Conducting polymers continue to be the focus of active research in diverse fields including electronics (Burroughes et al., 1988; Sailor et al., 1990; Gustafsson et al., 1992; Zhang et al., 1994), energy storage (Conway, 1991; Genies, 1991; Li et al., 1991), catalysis (Andrieux et al., 1982 ; Bull et al., 1983; Hable et al., 1993), chemical sensing (Josowicz et al., 1986; Heller, 1992; Gardner et al., 1993; Kuwabata et al., 1994; Freund et al., 1995) and biochemistry (Miller, 1988; Guimard et al., 2007). Despite the promise of these new materials and their widespread study, the scope of commercial uses remains small and relatively few viable technologies have emerged from the laboratory proof-of-concept stage. Limitations of processability such as low mechanical strength, poor flexibility and high cost have prevented conducting polymers from making significant commercial impact. In order to improve the processability of the conducting polymers, several approaches have been developed over the years: (1) synthesis of soluble conducting polymers by the addition of bulky side chains along the backbone (Wang et al., 2003), (2) synthesis in the form of colloidal dispersions by dispersion and emulsion polymerizations (Armes, 1998; Chehimi et al., 2004), (3) the use of metastable mixtures of monomer and oxidant that enable processability followed by in situ polymerization initiated by solvent evaporation (Grimaldo et al., 2007) and (4) fabrication of composite consisting of conducting polymers and substrates with high workability (Niwa et al., 1984; Paoli et al., 1984; Niwa et al., 1987; Yosomiya et al., 1986; Gregory et al., 1989; Heisey et al., 1993; Kuhn et al., 1995; Kincal et al., 1998; Appel et al., 1996; Collins et al., 1996; Kaynak et al., 2002; Han et al., 1999; Han et al., 2001; Dong et al., 2004; Dong et al., 2004; Abidian et al., 2006; Oh et al., 1999; Kim et al., 2002; Huang et al., 2005). There have been numerous reports on the deposition of air-stable conducting organic polymers such as polypyrrole (PPy), polyaniline (PANI), or poly(3,4ethylenedioxythiophene) (PEDOT) onto fibrous substrates (Gregory et al., 1989; Heisey et al., 1993; Kuhn et al., 1995; Kincal et al., 1998; Appel et al., 1996; Collins et al., 1996; Kaynak et al., 2002; Han et al., 1999; Han et al., 2001; Dong et al., 2004; Dong et al., 2004; Abidian et

“β-cis-SAr effect” on decarbonylation from α,β-unsaturated acyl and aroyl complexes

Lone pair of heteroatom located at the beta-cis position in alpha,beta-unsaturated acyl and aroyl group 10 metal complexes dramatically facilitated the stoichiometric and catalytic decarbonylation reactions.