- Hydrogenation of N-Heteroarenes Using Rhodium Precatalysts: Reductive Elimination Leads to Formation of Multimetallic Clusters
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A rhodium-catalyzed method for the hydrogenation of N-heteroarenes is described. A diverse array of unsubstituted N-heteroarenes including pyridine, pyrrole, and pyrazine, traditionally challenging substrates for hydrogenation, were successfully hydrogenated using the organometallic precatalysts, [(η5-C5Me5)Rh(N-C)H] (N-C = 2-phenylpyridinyl (ppy) or benzo[h]quinolinyl (bq)). In addition, the hydrogenation of polyaromatic N-heteroarenes exhibited uncommon chemoselectivity. Studies into catalyst activation revealed that photochemical or thermal activation of [(η5-C5Me5)Rh(bq)H] induced C(sp2)-H reductive elimination and generated the bimetallic complex, [(η5-C5Me5)Rh(μ2,η2-bq)Rh(η5-C5Me5)H]. In the presence of H2, both of the [(η5-C5Me5)Rh(N-C)H] precursors and [(η5-C5Me5)Rh(μ2,η2-bq)Rh(η5-C5Me5)H] converted to a pentametallic rhodium hydride cluster, [(η5-C5Me5)4Rh5H7], the structure of which was established by NMR spectroscopy, X-ray diffraction, and neutron diffraction. Kinetic studies on pyridine hydrogenation were conducted with each of the isolated rhodium complexes to identify catalytically relevant species. The data are most consistent with hydrogenation catalysis prompted by an unobserved multimetallic cluster with formation of [(η5-C5Me5)4Rh5H7] serving as a deactivation pathway.
- Kim, Sangmin,Loose, Florian,Bezdek, Máté J.,Wang, Xiaoping,Chirik, Paul J.
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p. 17900 - 17908
(2019/11/19)
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- Cobalt-Nanoparticles Catalyzed Efficient and Selective Hydrogenation of Aromatic Hydrocarbons
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The development of inexpensive and practical catalysts for arene hydrogenations is key for future valorizations of this general feedstock. Here, we report the development of cobalt nanoparticles supported on silica as selective and general catalysts for such reactions. The specific nanoparticles were prepared by assembling cobalt-pyromellitic acid-piperazine coordination polymer on commercial silica and subsequent pyrolysis. Applying the optimal nanocatalyst, industrial bulk, substituted, and functionalized arenes as well as polycyclic aromatic hydrocarbons are selectively hydrogenated to obtain cyclohexane-based compounds under industrially viable and scalable conditions. The applicability of this hydrogenation methodology is presented for the storage of H2 in liquid organic hydrogen carriers.
- Murugesan, Kathiravan,Senthamarai, Thirusangumurugan,Alshammari, Ahmad S.,Altamimi, Rashid M.,Kreyenschulte, Carsten,Pohl, Marga-Martina,Lund, Henrik,Jagadeesh, Rajenahally V.,Beller, Matthias
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p. 8581 - 8591
(2019/09/12)
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- Hydrogenation of Pyridines Using a Nitrogen-Modified Titania-Supported Cobalt Catalyst
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Novel heterogeneous catalysts were prepared by impregnation of titania with a solution of cobalt acetate/melamine and subsequent pyrolysis. The resulting materials show an unusual nitrogen-modified titanium structure through partial implementation of nitrogen into the support. The optimal catalyst displayed good activity and selectivity for challenging pyridine hydrogenation under acid free conditions in water as solvent.
- Chen, Feng,Li, Wu,Sahoo, Basudev,Kreyenschulte, Carsten,Agostini, Giovanni,Lund, Henrik,Junge, Kathrin,Beller, Matthias
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supporting information
p. 14488 - 14492
(2018/10/26)
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- NHC-stabilised Rh nanoparticles: Surface study and application in the catalytic hydrogenation of aromatic substrates
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New Rh-NPs stabilised by N-Heterocyclic Carbenes (NHC) were synthesized by decomposition of [Rh(η3-C3H5)3] under H2 atmosphere and fully characterized. Surface studies by FT-IR and NMR spectroscopy employing isotopically labelled ligands were also performed. The Rh0.2 NPs are active catalysts in the reduction of various aromatic substrates. In the reduction of phenol, high selectivities to cyclohexanone or cyclohexanol were obtained depending on the reaction conditions. However, this catalytic system exhibited much lower activity in the hydrogenation of substituted phenols. Pyridine was easily hydrogenated under mild conditions and interestingly, the hydrogenation of 4-methyl and 4-trifluoromethylpyridine resulted slower than that of 2-methylpyridine. The hydrogenation of 1-(pyridin-2-yl)propan-2-one provided the β-enaminone 13a in high yield as a consequence of the partial reduction of the pyridine ring followed by isomerization. Quinoline could be either partially hydrogenated to 1,2,3,4-tetrahydroquinoline or fully reduced to decahydroquinoline by adjusting the reaction conditions.
- Martinez-Espinar, Francisco,Blondeau, Pascal,Nolis, Pau,Chaudret, Bruno,Claver, Carmen,Castillón, Sergio,Godard, Cyril
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p. 113 - 127
(2017/09/08)
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- Catalytic Hydrogenation of Arenes in Water Over In Situ Generated Ruthenium Nanoparticles Immobilized on Carbon
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We describe a tandem process to generate active Ru nanoparticles (≈7 nm) immobilised in situ on carbon from an organometallic precursor and formic acid to afford the hydrogenation of a wide range of arenes and heteroarenes in yields up to 72 % with high conversions and selectivities for the desired products. The hydrogenation of several substrates analogous to lignin-derived fragments to the corresponding alicyclic products was also achieved. Our experimental investigations evidenced that the observed enhanced activity for arene hydrogenation was driven by the unique structural advantages of the organometallic precursor to activate formic acid, in which the presence of a nitrogen ligand is crucial to achieve a high catalytic activity. TEM analysis revealed the formation of Ru0 nanoparticles, and Hg0 poisoning experiments support the heterogeneous nature of the active catalyst.
- Dwivedi, Ambikesh Dhar,Rai, Rohit Kumar,Gupta, Kavita,Singh, Sanjay Kumar
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p. 1930 - 1938
(2017/06/13)
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- Selective hydrogenation of N-heterocyclic compounds using Ru nanocatalysts in ionic liquids
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N-Heterocyclic compounds have been tested in the selective hydrogenation catalysed by small 1-3 nm sized Ru nanoparticles (NPs) embedded in various imidazolium based ionic liquids (ILs). Particularly a diol-functionalised IL shows the best performance in the hydrogenation of quinoline to 1,2,3,4-tetrahydroquinoline (1THQ) with up to 99% selectivity.
- Konnerth, Hannelore,Prechtl, Martin H. G.
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supporting information
p. 2762 - 2767
(2017/07/24)
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- A One-Pot Process for the Enantioselective Synthesis of Amines via Reductive Amination under Transfer Hydrogenation Conditions
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(Equation presented) Cyclic amines may be prepared via a sequence of deprotection followed by intramolecular reductive amination of t-Boc-protected amino ketones under asymmetric transfer hydrogenation conditions. In cases where the corresponding imine reaction proceeds with high enantioselectivity, this is reflected in the one-step process.
- Williams, Glynn D.,Pike, Richard A.,Wade, Charles E.,Wills, Martin
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p. 4227 - 4230
(2007/10/03)
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- Functionalization of nitrogen and oxygen containing heterocycles by mercury photosensitized dehydrodimerizations
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Nitrogen and oxygen containing heterocycles can be functionalized by mercury photosensitization.
- Ferguson, Richard R.,Boojamra, Constantine G.,Brown, Stephen H.,Crabtree, Robert H.
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p. 121 - 124
(2007/10/02)
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- Facile Reduction of Pyridines with Nickel-Aluminum Alloy
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Nickel-aluminum alloy in dilute base can be used to reduce a variety of pyridines, quinolines, and isoquinoline to the corresponding piperidines, 1,2,3,4-tetrahydroquinolines, and 1,2,3,4-tetrahydroisoquinoline in good yield.The reaction is simple to perform, and high temperatures, high pressures, or hydrogen atmospheres are not required.The reaction is accelerated by substituents in the 2-position and by electron-withdrawing groups in the 3- and 4-positions while electron-supplying groups in the 3- and 4-positions retard the reaction.The major product isolated from the reduction of 2-phenylpyridine was 2-cyclohexylpiperidine hydrochloride.With isoniazid (1) and iproniazid (4) the pyridine ring is hydrogenated before the hydrazine is cleaved.
- Lunn, George,Sansone, Eric B.
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p. 513 - 517
(2007/10/02)
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- 3-(Piperidino-lower-alkyl)-indoles
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1-Acyl-3-(amino-lower-alkyl)indoles, useful as anti-inflammatory agents, are prepared either by acylation of a 3-(amino-lower-alkyl)indole; by Fisher indole synthesis from an N'-acylphenylhydrazine and an amino-lower-alkanone; by alkylation of an amine with a 1-acyl-3-(halo-lower-alkyl)indole; or by reductive alkylation of a 1-acyl-3-indole-lower-alkylcarboxaldehyde.
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- Phenyl-lower-alkylamines
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Phenyl-lower-alkylamines having anti-inflammatory activity are prepared either by reductive alkylation of an amine with a phenyl-lower-alkanaldehyde; by condensation of a phenyl-lower-alkanaldehyde with a secondary amine, conversion of the resulting phenylvinylamine to the corresponding iminium salt, and reduction of the latter with an alkali metal borohydride; or by reaction of a phenyl-lower-alkanoyl halide with an amine and reduction of the resulting amide with a reagent effective to reduce an amide to an amine.
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