Search

Abstract: Palladium nanoparticles supported on 5 %‐nitrogen‐doped, herringbone‐type carbon nanofibers (Pd/N‐CNF‐H), which are prepared by thermally decomposing [Pd2(dba)3⋅CHCl3] (dba=dibenzylideneacetone) in toluene in the presence of N‐CNF‐H, were found to be an efficient catalyst for the chemoselective hydrogenation of alkenyl and nitro moieties in benzyl‐protected alcohols and carboxylic acid derivatives with high turnover frequencies: the hydrogenation reactions of these functional groups proceeded smoothly even at ambient temperature under atmospheric H2 pressure, and the benzyl protecting groups in the molecules remained intact. Moreover, the recovered Pd/N‐CNF‐H catalyst could be reused without loss of its catalytic activity or chemoselectivity. The Pd/N‐CNF‐H catalyst also acted as an effective hydrogenation catalyst for the reduction of aromatic ketones to the corresponding benzyl alcohol derivatives with good to high product selectivity. [ABSTRACT FROM AUTHOR]

Combination of PdCl2 with 1,1,3,3‐tetramethyldisiloxane in the presence of activated carbon was found to be an effective catalyst system for the cleavage reaction of C−O bond of O−t‐Bu moieties. The present catalytic reaction offers a practical method for the deprotection of tert‐butyl esters, tert‐butyl ethers, O‐Boc, and N‐Boc derivatives under mild conditions. The addition of activated carbon in the reaction mixture was proved to be crucial for not only sustaining the catalytic activity but also trapping the palladium species after the reaction. [ABSTRACT FROM AUTHOR]

The easy synthesis of transition metal nanoparticles supported on three types of carbon nanofibers (platelet: CNF-P, tubular: CNF-T, herringbone: CNF-H) and nitrogen-doped CNF-H (N-CNF-H) is accomplished by pyrolysis of metal carbonyl clusters such as Ru 3 (CO) 12 , Rh 4 (CO) 12 , and Ir 4 (CO) 12 , and alkene complexes such as Pd 2 (dba) 3 ·CHCl 3 and Pt(dba) 2 [dba: dibenzylideneacetone]. Transmission electron microscopy of these CNFs with immobilized metal nanoparticles (M/CNFs and M/ N -CNF-H) showed that metal nanoparticles whose size could be controlled, existed on the CNFs, and that their location was dependent on the surface nanostructure of the CNFs: on the edge of the graphite layers (CNF-P), in the tubes and on the surface (CNF-T), and between the layers and on the edge (CNF-H). Among these M/CNFs, Ru/CNF-P and Rh/CNF-T showed excellent catalytic activity towards arene hydrogenation with high reusability and functional group tolerance, while the Pt/CNF-P behaves as an efficient catalyst for the hydrogenation of substituted nitroarenes to the corresponding aniline derivatives with the other functional groups remaining intact. Pt and Pd nanoparticles supported on N -CNF-H act as poisoning catalysts for the transformation of internal alkynes to ( Z )-alkenes over Pd/ N -CNF-H, and for the transformation of nitroarenes to the corresponding anilines and N -hydroxylamines over Pt/ N -CNF-H. [TANSO 2015 (No. 266) 35–40.] [ABSTRACT FROM AUTHOR]

Carbon‐nitrogen bond formation is an important method on both laboratory and industrial scales because it realizes the production of valuable pharmaceuticals, agrochemicals, and fine chemicals. Direct reductive N‐alkylation of amines with carbonyl compounds via intermediary imine compounds, especially under catalytic hydrogenation conditions, is one of the most convenient, economical, and environmentally friendly methods for this process. Here we report a novel palladium species on zirconia having specific activity towards hydrogenation of imines but other carbonyl groups remaining intact. The present catalytic property offers a practical synthetic method of functionalized secondary amines by reductive N‐alkylation under mild conditions with high atom‐efficiency. Mechanistic studies revealed that the catalytically active species is the palladium cluster, which is generated in situ from molecular palladium complexes on the support by exposure to atmospheric hydrogen. These fundamental findings are expected to progress in developing novel cluster catalysts for chemical processes directed towards a sustainable society. [ABSTRACT FROM AUTHOR]