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- ItemRhodium-catalyzed borylative carbon monoxide reduction to gem-diborylmethane(Amsterdam [u.a.] : Elsevier, 2021) Xua, Jian-Xing; Wu, Fu-Peng; Wu, Xiao-FengHerein, we developed a rhodium-catalyzed reduction of CO with bis(pinacolato)diboron (B2pin2) under atmospheric pressure of CO with silane as the hydride source, gem-diborylmethane [H2C(Bpin)2] as a versatile and fundamental C1 compound can be formed. Notably, this is the first example on transition metal-catalyzed borylation of CO. © 2020 The Author(s)
- ItemSynthesis of flow‐compatible Ru-Me/Al2O3 catalysts and their application in hydrogenation of 1-iodo-4-nitrobenzene([Cham] : Springer International Publishing, 2021) Sebek, Michael; Atia, Hanan; Steinfeldt, NorbertThe development of an active, selective, and long-term stable heterogeneous catalyst for the reductive hydrogenation of substituted nitrorarenes in continuous operation mode is still challenging. In this work, Ru based nanoparticles catalysts promoted with different transition metals (Zn, Co, Cu, Sn, or Fe) were supported on alumina spheres using spray wet impregnation method. The freshly prepared catalysts were characterized using complementary methods including scanning transmission electron microscopy (STEM) and temperature programmed reduction (TPR). The hydrogenation of 1-iodo-4-nitrobenzene served as model reaction to assess the catalytic performance of the prepared catalysts. The addition of the promotor affected the reducibility of Ru nanoparticles as well as the performance of the catalyst in the hydrogenation reaction. The highest yield of 4-iodoaniline (89 %) was obtained in a continuous flow process using Ru-Sn/Al2O3. The performance of this catalyst was also followed in a long-term experiment. With increasing operation time, a catalyst deactivation occurred which could only briefly compensate by an increase of the reaction temperature.
- ItemIndirect reduction of CO2 and recycling of polymers by manganese-catalyzed transfer hydrogenation of amides, carbamates, urea derivatives, and polyurethanes(Cambridge : RSC, 2021) Liu, Xin; Werner, ThomasThe reduction of polar bonds, in particular carbonyl groups, is of fundamental importance in organic chemistry and biology. Herein, we report a manganese pincer complex as a versatile catalyst for the transfer hydrogenation of amides, carbamates, urea derivatives, and even polyurethanes leading to the corresponding alcohols, amines, and methanol as products. Since these compound classes can be prepared using CO2as a C1 building block the reported reaction represents an approach to the indirect reduction of CO2. Notably, these are the first examples on the reduction of carbamates and urea derivatives as well as on the C-N bond cleavage in amides by transfer hydrogenation. The general applicability of this methodology is highlighted by the successful reduction of 12 urea derivatives, 26 carbamates and 11 amides. The corresponding amines, alcohols and methanol were obtained in good to excellent yields up to 97%. Furthermore, polyurethanes were successfully converted which represents a viable strategy towards a circular economy. Based on control experiments and the observed intermediates a feasible mechanism is proposed. © The Royal Society of Chemistry 2021.
- ItemSelective Earth-Abundant System for CO2 Reduction: Comparing Photo- and Electrocatalytic Processes(Washington, DC : American Chemical Society, 2019) Steinlechner C.; Roesel A.F.; Oberem E.; Päpcke A.; Rockstroh N.; Gloaguen F.; Lochbrunner S.; Ludwig R.; Spannenberg A.; Junge H.; Francke R.; Beller M.The valorization of CO2 via photo- or electrocatalytic reduction constitutes a promising approach toward the sustainable production of fuels or value-added chemicals using intermittent renewable energy sources. For this purpose, molecular catalysts are generally studied independently with respect to the photo- or the electrochemical application, although a unifying approach would be much more effective with respect to the mechanistic understanding and the catalyst optimization. In this context, we present a combined photo- and electrocatalytic study of three Mn diimine catalysts, which demonstrates the synergistic interplay between the two methods. The photochemical part of our study involves the development of a catalytic system containing a heteroleptic Cu photosensitizer and the sacrificial BIH reagent. The system shows exclusive selectivity for CO generation and renders turnover numbers which are among the highest reported thus far within the group of fully earth-abundant photocatalytic systems. The electrochemical part of our investigations complements the mechanistic understanding of the photochemical process and demonstrates that in the present case the sacrificial reagent, the photosensitizer, and the irradiation source can be replaced by the electrode and a weak Brønsted acid. © 2019 American Chemical Society.
- ItemIntermetallic nickel silicide nanocatalyst—A non-noble metal–based general hydrogenation catalyst(Washington, DC [u.a.] : Assoc., 2018) Ryabchuk, Pavel; Agostini, Giovanni; Pohl, Marga-Martina; Lund, Henrik; Agapova, Anastasiya; Junge, Henrik; Junge, Kathrin; Beller, MatthiasHydrogenation reactions are essential processes in the chemical industry, giving access to a variety of valuable compounds including fine chemicals, agrochemicals, and pharmachemicals. On an industrial scale, hydrogenations are typically performed with precious metal catalysts or with base metal catalysts, such as Raney nickel, which requires special handling due to its pyrophoric nature. We report a stable and highly active intermetallic nickel silicide catalyst that can be used for hydrogenations of a wide range of unsaturated compounds. The catalyst is prepared via a straightforward procedure using SiO2 as the silicon atom source. The process involves thermal reduction of Si–O bonds in the presence of Ni nanoparticles at temperatures below 1000°C. The presence of silicon as a secondary component in the nickel metal lattice plays the key role in its properties and is of crucial importance for improved catalytic activity. This novel catalyst allows for efficient reduction of nitroarenes, carbonyls, nitriles, N-containing heterocycles, and unsaturated carbon–carbon bonds. Moreover, the reported catalyst can be used for oxidation reactions in the presence of molecular oxygen and is capable of promoting acceptorless dehydrogenation of unsaturated N-containing heterocycles, opening avenues for H2 storage in organic compounds. The generality of the nickel silicide catalyst is demonstrated in the hydrogenation of over a hundred of structurally diverse unsaturated compounds. The wide application scope and high catalytic activity of this novel catalyst make it a nice alternative to known general hydrogenation catalysts, such as Raney nickel and noble metal–based catalysts.