Yukihiro Motoyama

Chemoselective hydrogenation of nitroarenes with carbon nanofiber-supported platinum and palladium nanoparticles.

Platinum and palladium nanoparticles supported on three types of carbon nanofibers (CNFs) are synthesized and used as catalysts in the hydrogenation of nitroarenes. Nanosized platinum particles dispersed on platelet-type CNF efficiently catalyze the reduction of functionalized nitroarenes to the corresponding substituted anilines in high turnover numbers with other functional groups remaining intact.

Practical Access to Amines by Platinum-Catalyzed Reduction of Carboxamides with Hydrosilanes: Synergy of Dual Si−H Groups Leads to High Efficiency and Selectivity

The synergetic effect of two Si-H groups leads to efficient reduction of carboxamides to amines by platinum catalysts under mild conditions. The rate of the reaction is dependent on the distance of two Si-H groups; 1,1,3,3-tetramethyldisiloxane (TMDS) and 1,2-bis(dimethylsilyl)benzene are found to be an effective reducing reagent. The reduction of amides having other reducible functional groups such as NO(2), CO(2)R, CN, C horizontal lineC, Cl, and Br moieties proceeds with these groups remaining intact, providing a reliable method for the access to functionalized amine derivatives. The platinum-catalyzed reduction of amides with polymethylhydrosiloxane (PMHS) also proceeds under mild conditions. The reaction is accompanied by automatic removal of both platinum and silicon wastes as insoluble silicone resin, and the product is obtained by simple extraction. A mechanism involving double oxidative addition of TMDS to a platinum center is discussed.

Highly efficient synthesis of aldenamines from carboxamides by iridium-catalyzed silane-reduction/dehydration under mild conditions

The combination of IrCl(CO)(PPh3)2 with 1,1,3,3-tetramethyldisiloxane or poly(methylhydrosiloxane) (PMHS) is found to be an efficient catalyst system for the preparation of aldenamines from carboxamides; in particular, facile removal of silicone and iridium residues from the product can be achieved by the use of PMHS.

Catalysis in Polysiloxane Gels: Platinum-Catalyzed Hydrosilylation of Polymethylhydrosiloxane Leading to Reusable Catalysts for Reduction of Nitroarenes

Novel polysiloxane gels, to which platinum species are encapsulated, are prepared by treatment of polymethylhydrosiloxane with alkenes in the presence of Karstedts catalyst. These gels act as reusable catalysts in the reduction of functionalized nitroarenes with H(2) to the corresponding substituted anilines without leaking the catalyst species.

Chiral titanium complex-catalyzed Diels-Alder reaction: A practical route to anthracycline intermediates

Abstract Asymmetric Diels-Alder reactions of methacrolein and 1,4-naphthoquinone with 1,3-dienol derivatives catalyzed by the chiral binaphthol (BINOL)-derived titanium complex 1 are shown to provide the corresponding endo -adducts in high enantiomeric purity. The naphthoquinone adduct can serve as a synthetic intermediate of tetracycline antibiotics.

Platinum Nanoparticles Supported on Nitrogen‐doped Carbon Nanofibers as Efficient Poisoning Catalysts for the Hydrogenation of Nitroarenes

Carbon-supported metal nanoparticles are widely used as sensors, electrocatalysts for fuel cells and Li ion batteries, or heterogeneous catalysts for various organic transformations. Since the catalytic properties of these materials are highly dependent on the supports, numerous studies have been performed to modify the carbon supports to improve their catalyst performances. 2] One method to tailor the chemical and/or physical properties and stabilize metal nanoparticles–support interactions involves the chemical modification of the carbon surface by introduction of functional groups or the doping of heteroatoms. For example, the addition of sulfur, nitrogen, phosphorous, or halogen containing compounds as a catalyst poison to the original catalyst often retards the reaction rate, but sometimes also suppresses possible side reactions, thereby leading to highly selective organic transformations. 6] Another way to improve the catalyst performance is the use of carbon nanomaterials as a support, because their nanolevel controlled surface structures lead to the immobilization of highly dispersed metal nanoparticles with narrow size distributions and high conductivity. We previously reported the synthesis and application of metal nanoparticles supported on carbon nanofibers (CNFs) in hydrogenation catalysts. CNFs are classified into three types, in which the graphite layers are perpendicular (platelet: CNFP), parallel (tubular : CNF-T), or stacked obliquely (herringbone: CNF-H). Among these metal-supported CNFs (M/CNF; M = Ru, Rh, Pd, and Pt), Pt/CNF-P and Pt/CNF-H were proven to act as reusable catalysts for the nitro-selective reduction of halonitrobenzenes to the corresponding haloanilines with high turnover numbers in the presence of n-octylamine (OctNH2) as a catalyst poison. Because of these results, we were interested in nitrogen-doped CNF as a support for metal nanoparticles. The combination of carbon nanostructures and the doping of nitrogen atoms are expected to offer an efficient poisoning catalyst for chemoselective catalytic reactions. In this paper, we report that platinum nanoparticles can be immobilized on the surface of nitrogen-doped, herringbone-type carbon nanofibers (N-CNFH), and the formed Pt/N-CNF-H compounds are highly efficient reusable catalysts for the nitro-selective hydrogenation of functionalized nitroarenes. N-CNF-H was synthesized by using chemical vapor deposition over a MgO supported Ni–Fe catalyst using acetonitrile and hydrogen at 530 8C, as reported previously. Elemental analysis of N-CNF-H revealed the amount of nitrogen incorporated into N-CNF-H to be approximately 5 wt %. Immobilization of platinum particles (metal loadings of ca. 1 and 3 wt %) on NCNF-H was performed by applying the same method as for Pt/ CNF, that is, by thermally decomposing [Pt(dba)2] (dba = dibenzylideneacetone) in toluene in the presence of N-CNF-H under an argon atmosphere (Scheme 1).

Rhodium nanoparticles supported on carbon nanofibers as an arene hydrogenation catalyst highly tolerant to a coexisting epoxido group.

Rhodium nanoparticles supported on a carbon nanofiber (Rh/CNF-T) show high catalytic activity toward arene hydrogenation under mild conditions in high turnover numbers without leaching the Rh species; the reaction is highly tolerant to epoxido groups, which often undergo ring-opening hydrogenation with conventional catalysts.

Single-chiral bis(oxazolinyl)pyridine (pybox). Efficiency in asymmetric catalytic cyclopropanation

Abstract Single-chiral bis(oxazolinyl)pyridine ligands were examined as ligands for ruthenium-catalyzed asymmetric catalytic cyclopropanation of olefins: enantioselectivities up to 94% for the trans -cyclopropane were observed.

Asymmetric hetero Diels–Alder reaction of Danishefsky's dienes and glyoxylates with chiral bis(oxazolinyl)phenylrhodium(III) aqua complexes, and its mechanistic studies

Abstract Asymmetric hetero Diels–Alder reaction of Danishefskys dienes with glyoxylates is catalyzed in high enantioselectivity and cis (endo)-diastereoselectivity by chiral (Phebox)RhCl2(H2O) complexes [Phebox=2,6-bis(oxazolinyl)phenyl], via the concerted [4+2] mechanism with perpendicular conformation of two carbonyl moieties of glyoxylates. Dibromide and difluoride complexes were newly synthesized and found to exhibit a slightly higher enantioselectivity of the hetero Diels–Alder products than the parent dichloride complex (Cl: 80% ee, Br: 82% ee, F: 84% ee).

Diastereoselective and enantioselective glyoxylate-ene reaction catalyzed by new class of binaphthol-derived titanium complex

Diastereo- and enantioselective carbonyl-ene reaction of glyoxylate (2) with trisubstituted olefins (3) catalyzed by chiral titanium complexes (1a), derived from 6,6′-dibromo-1,1′-bi-2-naphthol and diisopropoxytitanium dihalides, is found to provide syn-diastereomers exclusively along with a high level of enantioselectivity.