No abstract

Incorporation of silicon atoms into nickel nanoparticles boosts the catalytic activity for (de)hydrogenation reactions.

Methanol synthesis from syngas (CO/H 2 mixtures) is one of the largest manmade chemical processes with annual production reaching 100 million tons. The current industrial method proceeds at high temperatures (200−300 °C) and pressures (50−100 atm) using a copper−zinc-based heterogeneous catalyst. In contrast, here, we report a molecularly defined manganese catalyst that allows for low-temperature/lowpressure (120−150 °C, 50 bar) carbon monoxide hydrogenation to methanol. This new approach was evaluated and optimized by quantum mechanical simulations virtual high-throughput screenings. Crucial for this achievement is the use of amine-based promoters, which capture carbon monoxide to give formamide intermediates, which then undergo manganese-catalyzed hydrogenolysis, regenerating the promoter. Following this conceptually new approach, high selectivity toward methanol and catalyst turnover numbers (up to 3170) was achieved. The proposed general catalytic cycle for methanol synthesis is supported by model studies and detailed spectroscopic investigations.

Nickel catalyst for hydrogen storage in N-heterocycles: a heterogeneous nickel catalyst promotes both hydrogenation and subsequent dehydrogenation of quinoline derivatives.

The enantioselective dichlorination of alkenes is a continuing challenge in organic synthesis owing to the limitations of selective and independent antarafacial delivery of both electrophilic chlorenium and nucleophilic chloride to an olefin. Development of a general method for the enantioselective dichlorination of isolated alkenes would allow access to a wide variety of polyhalogenated natural products. Accordingly, the enantioselective suprafacial dichlorination of alkenes catalyzed by electrophilic organoselenium reagents has been developed to address these limitations. The evaluation of twenty-three diselenides as precatalysts for enantioselective dichlorination is described, with a maximum e.r. of 76:24 Additionally, mechanistic studies suggest an unexpected Dynamic Kinetic Asymmetric Transformation (DyKAT) process may be operative.

A highly chemo- and diastereoselective protocol toward amino-substituted donor-acceptor cyclopropanes via the formal nucleophilic displacement in bromocyclopropanes is described. A wide range of N-nucleophiles, including carboxamides, sulfonamides, azoles, and anilines, can be efficiently employed in this transformation, providing expeditious access to stereochemically defined and densely functionalized cyclopropylamine derivatives.

Hydrodehalogenation is an effective strategy for transforming persistent and potentially toxic organohalides into their more benign congeners. Common methods utilize Pd/C or Raney‐nickel as catalysts, which are either expensive or have safety concerns. In this study, a nickel‐based catalyst supported on titania (Ni‐phen@TiO2‐800) is used as a safe alternative to pyrophoric Raney‐nickel. The catalyst is prepared in a straightforward fashion by deposition of nickel(II)/1,10‐phenanthroline on titania, followed by pyrolysis. The catalytic material, which was characterized by SEM, TEM, XRD, and XPS, consists of nickel nanoparticles covered with N‐doped carbon layers. By using design of experiments (DoE), this nanostructured catalyst is found to be proficient for the facile and selective hydrodehalogenation of a diverse range of substrates bearing C−I, C−Br, or C−Cl bonds (>30 examples). The practicality of this catalyst system is demonstrated by the dehalogenation of environmentally hazardous and polyhalogenated substrates atrazine, tetrabromobisphenol A, tetrachlorobenzene, and a polybrominated diphenyl ether (PBDE).

Ab ifunctional 3d-metal catalyst for the cascade synthesis of diverse pyrroles from nitroarenes is presented. The optimal catalytic system Co/NGr-C@SiO 2-L is obtained by pyrolysis of ac obalt-impregnated composite followed by subsequent selective leaching.I nt he presence of this material, (transfer) hydrogenation of easily available nitroarenes and subsequent Paal-Knorr/Clauson-Kass condensation provides > 40 pyrroles in good to high yields using dihydrogen, formic acid, or aC O/H 2 Om ixture (WGSR conditions) as reductant. In addition to the favorable step economy,this straightforward domino process does not require any solvents or external cocatalysts.The general synthetic utility of this methodology was demonstrated on avariety of functionalizedsubstrates including the preparation of biologically active and pharmaceutically relevant compounds,for example,(+ +)-Isamoltane.