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09 Sep 11:41

Pincer-Type Complexes for Catalytic (De)Hydrogenation and Transfer (De)Hydrogenation Reactions: Recent Progress

by Svenja Werkmeister, Jacob Neumann, Kathrin Junge, Matthias Beller

Abstract

Pincer complexes are becoming increasingly important for organometallic chemistry and organic synthesis. Since numerous applications for such catalysts have been developed in recent decades, this Minireview covers progress in their use as catalysts for (de)hydrogenation and transfer (de)hydrogenation reactions during the last four years. Aside from noble-metal-based pincer complexes, the corresponding base metal complexes are also highlighted and their applications summarized.

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Pincers of power: This minireview is focused on the recent progress of the application of various precious and non-precious metal pincer-type catalysts. Besides hydrogenation reactions, their utilization for dehydrogenation and transfer (de)hydrogenation reactions is also described. Especially, but not exclusively, the usage of ruthenium and iron pincer complexes is highlighted for C[BOND]C, C[BOND]N, and C[BOND]O bond transformations.

09 Sep 08:55

Highly Selective Hydrogenation of Aromatic Ketones and Phenols Enabled by Cyclic (Amino)(alkyl)carbene Rhodium Complexes

by Yu Wei, Bin Rao, Xuefeng Cong and Xiaoming Zeng

TOC Graphic

Journal of the American Chemical Society
DOI: 10.1021/jacs.5b05868
09 Sep 08:55

Direct Ruthenium-catalyzed Hydrogenation of Carboxylic Acids to Alcohols

by Xinjiang Cui, Yuehui Li, Christoph Topf, Kathrin Junge, Matthias Beller

Abstract

The “green” reduction of carboxylic acids to alcohols is a challenging task in organic chemistry. Herein, we describe a general protocol for generation of alcohols by catalytic hydrogenation of carboxylic acids. Key to success is the use of a combination of Ru(acac)3, triphos and Lewis acids. The novel method showed broad substrate tolerance and a variety of aliphatic carboxylic acids including biomass-derived compounds can be smoothly reduced.

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Direct route to alcohols: The combination of a specific ruthenium complex and Lewis acids is found to be active for the direct hydrogenation of carboxylic acids to alcohols. A variety of carboxylic acids including biomass-based derivatives are converted into the desired alcohols in high yields.

09 Sep 08:55

Convergent reductive depolymerization of wood lignin to isolated phenol derivatives by metal-free catalytic hydrosilylation

Energy Environ. Sci., 2015, 8,2734-2743
DOI: 10.1039/C5EE01304F, Paper
Elias Feghali, Geraldine Carrot, Pierre Thuery, Caroline Genre, Thibault Cantat
Convergent reductive depolymerization of wood lignin to isolated phenol derivatives by metal-free catalytic hydrosilylation.
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09 Sep 08:54

Rechargeable Hydrogen Storage System Based on the Dehydrogenative Coupling of Ethylenediamine with Ethanol

by Peng Hu, Yehoshoa Ben-David, David Milstein

Abstract

A novel and simple hydrogen storage system was developed, based on the dehydrogenative coupling of inexpensive ethylenediamine with ethanol to form diacetylethylenediamine. The system is rechargeable and utilizes the same ruthenium pincer catalyst for both hydrogen loading and unloading procedures. It is efficient and uses a low catalyst loading. Repetitive reversal reactions without addition of new catalyst result in excellent conversions in both the dehydrogenation and hydrogenation procedures in three cycles.

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In support of the hydrogen economy: An efficient and simple homogeneous hydrogen carrier system was developed based on the dehydrogenative coupling of ethylenediamine with ethanol to form diacetylethylenediamine. The same ruthenium pincer catalyst is used for both hydrogen loading and unloading reactions.

09 Sep 08:54

Iron-Catalyzed Reduction of CO2 into Methylene: Formation of C–N, C–O, and C–C Bonds

by Guanghua Jin, C. Gunnar Werncke, Yannick Escudié, Sylviane Sabo-Etienne and Sébastien Bontemps

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Journal of the American Chemical Society
DOI: 10.1021/jacs.5b06077
09 Sep 08:54

[Report] Metal-free catalytic C-H bond activation and borylation of heteroarenes

by Marc-André Légaré
Transition metal complexes are efficient catalysts for the C-H bond functionalization of heteroarenes to generate useful products for the pharmaceutical and agricultural industries. However, the costly need to remove potentially toxic trace metals from the end products has prompted great interest in developing metal-free catalysts that can mimic metallic systems. We demonstrated that the borane (1-TMP-2-BH2-C6H4)2 (TMP, 2,2,6,6-tetramethylpiperidine) can activate the C-H bonds of heteroarenes and catalyze the borylation of furans, pyrroles, and electron-rich thiophenes. The selectivities complement those observed with most transition metal catalysts reported for this transformation. Authors: Marc-André Légaré, Marc-André Courtemanche, Étienne Rochette, Frédéric-Georges Fontaine
09 Sep 08:53

Transition Metal-Catalyzed CH Activation of Indoles

by Alexander H. Sandtorv

Abstract

The last decades have seen a tremendous expanse in the application of C[BOND]H activation of many different substrate classes, including the invaluable indole scaffold. Following the exciting emergence of C[BOND]H activation as a multi-faceted platform for functionalization, a versatile tool box has been developed for the preparation of structurally diverse indoles. This review article discusses recent advances and strategies for transition metal-catalyzed C[BOND]H activation of indoles.

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10 Apr 11:28

Sustainable conversion of carbon dioxide: the advent of organocatalysis

Green Chem., 2015, 17,1375-1389
DOI: 10.1039/C4GC01959H, Tutorial Review
Giulia Fiorani, Wusheng Guo, Arjan W. Kleij
The conversion of carbon dioxide (CO2), an abundant renewable carbon reagent, into chemicals of academic and industrial interest is of imminent importance to create a higher degree of sustainability in chemical processing and production.
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10 Apr 11:28

Nickel-Catalyzed Monoarylation of Ammonia

by Andrey Borzenko, Nicolas L. Rotta-Loria, Preston M. MacQueen, Christopher M. Lavoie, Robert McDonald, Mark Stradiotto

Abstract

Structurally diverse (hetero)aryl chloride, bromide, and tosylate electrophiles were employed in the Ni-catalyzed monoarylation of ammonia, including chemoselective transformations. The employed JosiPhos/[Ni(cod)2] catalyst system enables the use of commercially available stock solutions of ammonia, or the use of ammonia gas in these reactions, thereby demonstrating the versatility and potential scalability of the reported protocol. Proof-of-principle experiments established that air-stable [(JosiPhos)NiCl2] precatalysts can be employed successfully in such transformations.

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Lighten Up: The substrate scope of the title reaction includes (hetero)aryl chloride, bromide, and tosylate electrophiles. The versatility and potential scalability of the reported protocol is demonstrated by the use of either commercially available stock solutions of ammonia or ammonia gas.

10 Apr 11:26

Chemoselective Hydrogenation of Carbonyl Compounds and Acceptorless Dehydrogenative Coupling of Alcohols

by Denis Spasyuk, Cristian Vicent and Dmitry G. Gusev

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Journal of the American Chemical Society
DOI: 10.1021/ja512389y
10 Apr 11:26

[Report] Design, synthesis, and carbon-heteroatom coupling reactions of organometallic nickel(IV) complexes

by Nicole M. Camasso
Homogeneous nickel catalysis is used for the synthesis of pharmaceuticals, natural products, and polymers. These reactions generally proceed via nickel intermediates in the Ni0, NiI, NiII, and/or NiIII oxidation states. In contrast, NiIV intermediates are rarely accessible. We report herein the design, synthesis, and characterization of a series of organometallic NiIV complexes, accessed by the reaction of NiII precursors with the widely used oxidant S-(trifluoromethyl)dibenzothiophenium triflate. These NiIV complexes undergo highly selective carbon(sp3)-oxygen, carbon(sp3)-nitrogen, and carbon(sp3)-sulfur coupling reactions with exogenous nucleophiles. The observed reactivity has the potential for direct applications in the development of nickel-catalyzed carbon-heteroatom coupling reactions. Authors: Nicole M. Camasso, Melanie S. Sanford
10 Apr 11:25

Iron-Catalyzed C–H Borylation of Arenes

by Thomas Dombray, C. Gunnar Werncke, Shi Jiang, Mary Grellier, Laure Vendier, Sébastien Bontemps, Jean-Baptiste Sortais, Sylviane Sabo-Etienne and Christophe Darcel

TOC Graphic

Journal of the American Chemical Society
DOI: 10.1021/jacs.5b00895
10 Apr 11:25

Highly Efficient Ruthenium-Catalyzed N-Formylation of Amines with H2 and CO2

by Lei Zhang, Zhaobin Han, Xiaoyu Zhao, Zheng Wang, Kuiling Ding

Abstract

A highly efficient catalyst system based on ruthenium-pincer-type complexes has been discovered for N-formylation of various amines with CO2 and H2, thus affording the corresponding formamides with excellent productivity (turnover numbers of up to 1 940 000 in a single batch) and selectivity. Using a simple catalyst recycling protocol, the catalyst was reused for 12 runs in N,N-dimethylformamide production without significant loss of activity, thus demonstrating the potential for practical utilization of this cost-effective process. A one-pot two-step procedure for hydrogenation of CO2 to methanol via the intermediacy of formamide formation has also been developed.

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Just a pinch: CO2 is efficiently hydrogenated for N-formylation of various amines using ruthenium-pincer catalysts, thus affording the corresponding formamides with extremely high turnover numbers (TONs). The catalyst was readily reused for 12 runs without significant loss of activity in N,N-dimethylformamide production, thus demonstrating potential for practical utilization of this cost-effective process.