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A General Regioselective Synthesis of Alcohols by Cobalt-Catalyzed Hydrogenation of Epoxides
A straightforward methodology for the synthesis of anti-Markovnikov-type alcohols is presented. By using a specific cobalt triphos complex in the presence of Zn(OTf)2 as an additive, the hydrogenation of epoxides proceeds with high yields and selectivities. The described protocol shows a broad substrate scope, including multi-substituted internal and terminal epoxides, as well as a good functional-group tolerance. Various natural-product derivatives, including steroids, terpenoids, and sesquiterpenoids, gave access to the corresponding alcohols in moderate-to-excellent yields. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
Ligand-Controlled Palladium-Catalyzed Carbonylation of Alkynols : Highly Selective Synthesis of α-Methylene-β-Lactones
The first general and regioselective Pd-catalyzed cyclocarbonylation to give α-methylene-β-lactones is reported. Key to the success for this process is the use of a specific sterically demanding phosphine ligand based on N-arylated imidazole (L11) in the presence of Pd(MeCN)2Cl2 as pre-catalyst. A variety of easily available alkynols provide under additive-free conditions the corresponding α-methylene-β-lactones in moderate to good yields with excellent regio- and diastereoselectivity. The applicability of this novel methodology is showcased by the direct carbonylation of biologically active molecules including natural products. © 2020 The Authors. Published by Wiley-VCH GmbH
Ruthenium-Catalyzed Site-Selective Trifluoromethylations and (Per)Fluoroalkylations of Anilines and Indoles
Introducing (per)fluoroalkyl groups into arenes continues to be an interesting, but challenging area in organofluorine chemistry. We herein report an ortho-selective C−H perfluoroalkylation including trifluoromethylations of anilines and indoles without the need of protecting groups using RfI and RfBr as commercially available reagents. The availability and price of the starting materials and the inherent selectivity make this novel methodology attractive for the synthesis of diverse (per)fluoroalkylated building blocks, for example, for bioactive compounds and materials. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
Iron/N-doped graphene nano-structured catalysts for general cyclopropanation of olefins
The first examples of heterogeneous Fe-catalysed cyclopropanation reactions are presented. Pyrolysis of in situ-generated iron/phenanthroline complexes in the presence of a carbonaceous material leads to specific supported nanosized iron particles, which are effective catalysts for carbene transfer reactions. Using olefins as substrates, cyclopropanes are obtained in high yields and moderate diastereoselectivities. The developed protocol is scalable and the activity of the recycled catalyst after deactivation can be effectively restored using an oxidative reactivation protocol under mild conditions. This journal is © The Royal Society of Chemistry.
Cobalt Single-Atom Catalysts with High Stability for Selective Dehydrogenation of Formic Acid
Metal–organic framework (MOF)-derived Co-N-C catalysts with isolated single cobalt atoms have been synthesized and compared with cobalt nanoparticles for formic acid dehydrogenation. The atomically dispersed Co-N-C catalyst achieves superior activity, better acid resistance, and improved long-term stability compared with nanoparticles synthesized by a similar route. High-angle annular dark-field–scanning transmission electron microscopy, X-ray photoelectron spectroscopy, electron paramagnetic resonance, and X-ray absorption fine structure characterizations reveal the formation of CoIINx centers as active sites. The optimal low-cost catalyst is a promising candidate for liquid H2 generation. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
Facile synthesis of iron-titanate nanocomposite as a sustainable material for selective amination of substitued nitro-arenes
The fabrication of durable and low-cost nanostructured materials remains important in chemical, biologic and medicinal applications. Particularly, iron-based nanomaterials are of central importance due to the ‘noble’ features of iron such as its high abundance, low cost and non-toxicity. Herein we report a simple sol–gel method for the synthesis of novel iron–titanium nanocomposite-based material (Fe9TiO15@TiO2). In order to prepare this material, we made a polymeric gel using ferrocene, titanium isopropoxide and THF precursors. The calcination of this gel in air at 500◦C produced Fe-Ti bimetallic nanoparticles-based composite and nano-TiO2 as support. Noteworthy, our methodology provides an excellent control over composition, size and shape of the resulting nanoparticles. The resulted Fe-based material provides a sustainable catalyst for selective synthesis of anilines, which are key intermediates for the synthesis of several chemicals, dyes and materials, via reduction of structurally diverse and functionalized nitroarenes. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.
Synthesis of Molybdenum Pincer Complexes and Their Application in the Catalytic Hydrogenation of Nitriles
A series of molybdenum(0), (I) and (II) complexes ligated by different PNP and NNN pincer ligands were synthesized and structurally characterized. Along with previously described Mo−PNP complexes Mo-1 and Mo-2, all prepared compounds were tested in the catalytic hydrogenation of aromatic nitriles to primary amines. Among the applied catalysts, Mo-1 is particularly well suited for the hydrogenation of electron-rich benzonitriles. Additionally, two aliphatic nitriles were transformed into the desired products in 80 and 86 %, respectively. Moreover, catalytic intermediate Mo-1a was isolated and its role in the catalytic cycle was subsequently demonstrated. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
Cascade Synthesis of Pyrroles from Nitroarenes with Benign Reductants Using a Heterogeneous Cobalt Catalyst
A bifunctional 3d-metal catalyst for the cascade synthesis of diverse pyrroles from nitroarenes is presented. The optimal catalytic system Co/NGr-C@SiO2-L is obtained by pyrolysis of a cobalt-impregnated composite followed by subsequent selective leaching. In the 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 a CO/H2O mixture (WGSR conditions) as reductant. In addition to the favorable step economy, this straightforward domino process does not require any solvents or external co-catalysts. The general synthetic utility of this methodology was demonstrated on a variety of functionalized substrates including the preparation of biologically active and pharmaceutically relevant compounds, for example, (+)-Isamoltane. © 2020 The Authors. Published by Wiley-VCH GmbH
Cyclometalated Ruthenium Pincer Complexes as Catalysts for the α-Alkylation of Ketones with Alcohols
Ruthenium PNP pincer complexes bearing supplementary cyclometalated C,N-bound ligands have been prepared and fully characterized for the first time. By replacing CO and H− as ancillary ligands in such complexes, additional electronic and steric modifications of this topical class of catalysts are possible. The advantages of the new catalysts are demonstrated in the general α-alkylation of ketones with alcohols following a hydrogen autotransfer protocol. Herein, various aliphatic and benzylic alcohols were applied as green alkylating agents for ketones bearing aromatic, heteroaromatic or aliphatic substituents as well as cyclic ones. Mechanistic investigations revealed that during catalysis, Ru carboxylate complexes are predominantly formed whereas neither the PNP nor the CN ligand are released from the catalyst in significant amounts. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
General and selective synthesis of primary amines using Ni-based homogeneous catalysts
The development of base metal catalysts for industrially relevant amination and hydrogenation reactions by applying abundant and atom economical reagents continues to be important for the cost-effective and sustainable synthesis of amines which represent highly essential chemicals. In particular, the synthesis of primary amines is of central importance because these compounds serve as key precursors and central intermediates to produce value-added fine and bulk chemicals as well as pharmaceuticals, agrochemicals and materials. Here we report a Ni-triphos complex as the first Ni-based homogeneous catalyst for both reductive amination of carbonyl compounds with ammonia and hydrogenation of nitroarenes to prepare all kinds of primary amines. Remarkably, this Ni-complex enabled the synthesis of functionalized and structurally diverse benzylic, heterocyclic and aliphatic linear and branched primary amines as well as aromatic primary amines starting from inexpensive and easily accessible carbonyl compounds (aldehydes and ketones) and nitroarenes using ammonia and molecular hydrogen. This Ni-catalyzed reductive amination methodology has been applied for the amination of more complex pharmaceuticals and steroid derivatives. Detailed DFT computations have been performed for the Ni-triphos based reductive amination reaction, and they revealed that the overall reaction has an inner-sphere mechanism with H2metathesis as the rate-determining step. © The Royal Society of Chemistry 2020.