- Highly effective and chemoselective hydrodeoxygenation of aromatic alcohols
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Effective hydrodeoxygenation (HDO) of aromatic alcohols is very attractive in both conventional organic synthesis and upgrading of biomass-derived molecules, but the selectivity of this reaction is usually low because of the competitive hydrogenation of the unsaturated aromatic ring and the hydroxyl group. The high activity of noble metal-based catalysts often leads to undesired side reactions (e.g., saturation of the aromatic ring) and excessive hydrogen consumption. Non-noble metal-based catalysts suffer from unsatisfied activity and selectivity and often require harsh reaction conditions. Herein, for the first time, we report chemoselective HDO of various aromatic alcohols with excellent selectivity, using porous carbon-nitrogen hybrid material-supported Co catalysts. The C-OH bonds were selectively cleaved while leaving the aromatic moiety intact, and in most cases the yields of targeted compounds reached above 99% and the catalyst could be readily recycled. Nitrogen doping on the carbon skeleton of the catalyst support (C-N matrix) significantly improved the yield of the targeted product. The presence of large pores and a high surface area also improved the catalyst efficiency. This work opens the way for efficient and selective HDO reactions of aromatic alcohols using non-noble metal catalysts.
- Han, Buxing,He, Mingyuan,Mei, Xuelei,Wu, Haihong,Wu, Wei,Xu, Caiyun,Zhai, Jianxin,Zhang, Kaili,Zhang, Zhanrong,Zheng, Bingxiao
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p. 1629 - 1635
(2022/02/21)
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- Reductive activation and hydrofunctionalization of olefins by multiphoton tandem photoredox catalysis
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The conversion of olefin feedstocks to architecturally complex alkanes represents an important strategy in the expedient generation of valuable molecules for the chemical and life sciences. Synthetic approaches are reliant on the electrophilic activation of unactivated olefins, necessitating functionalization with nucleophiles. However, the reductive functionalization of unactivated and less activated olefins with electrophiles remains an ongoing challenge in synthetic chemistry. Here, we report the nucleophilic activation of inert styrenes through a photoinduced direct single electron reduction to the corresponding nucleophilic radical anion. Central to this approach is the multiphoton tandem photoredox cycle of the iridium photocatalyst [Ir(ppy)2(dtbbpy)] PF6, which triggers in situ formation of a high-energy photoreductant that selectively reduces styrene olefinic π bonds to radical anions without stoichiometric reductants or dissolving metals. This mild strategy enables the chemoselective reduction and hydrofunctionalization of styrenes to furnish valuable alkane and tertiary alcohol derivatives. Mechanistic studies support the formation of a styrene olefinic radical anion intermediate and a Birch-type reduction involving two sequential single electron transfers. Overall, this complementary mode of olefin activation achieves the hydrofunctionalization of less activated alkenes with electrophiles, adding value to abundant olefins as valuable building blocks in modern synthetic protocols.
- Czyz, Milena L.,Taylor, Mitchell S.,Horngren, Tyra H.,Polyzos, Anastasios
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p. 5472 - 5480
(2021/06/01)
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- Copper(II)-Doped ZIF-8 as a Reusable and Size Selective Heterogeneous Catalyst for the Hydrogenation of Alkenes using Hydrazine Hydrate
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In recent years, synthesis of mixed-metal organic frameworks has received considerable attention due to their superior performance than with mono-metallic metal organic frameworks (MOFs). In the present manuscript, Cu2+ ions are doped within the framework of ZIF-8 (ZIF: Zeolitic Imidazolate Frameworks) to obtain Cu@ZIF-8 and is characterized by powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR), UV-Visible diffuse reflectance spectra (DRS), scanning electron microscope (SEM) and transmission electron microcope (TEM) studies. The reaction conditions are optimized with styrene as a model substrate using Cu@ZIF-8 as a solid catalyst. Heterogeneity of the reaction is confirmed by leaching test and the solid is reusable for three recycles with no diminishing activity. Further, the structural integrity of Cu@ZIF-8 is also retained after hydrogenation of styrene as evidenced by powder X-ray diffraction. The size selective catalysis of Cu@ZIF-8 is demonstrated by comparing the activity of Cu2+ ions adsorbed over ZIF-8 solid (Cu/ZIF-8) in the hydrogenation of 1-hexene, 1-octene, cyclohexene, cyclooctene and t-stilbene. The catalytic results indicate that Cu/ZIF-8 shows superior activity than Cu@ZIF-8 for all these olefins due to the lack of diffusion to access the active sites (Cu2+). In contrast, Cu@ZIF-8 exhibits higher activity for those olefins with lower molecular dimensions (1-hexene, 1-octene) than the pores of ZIF-8 indicating the facile diffusion of these substrates inside the pores ZIF-8 while poor activity is observed with t-stilbene due to its larger molecular dimension than the pore apertures of ZIF-8. These catalytic data clearly establish the size selective hydrogenation of Cu@ZIF-8 due to the effective confinement provided by ZIF-8 framework and the presence of the active sites within the framework. Furthermore, this is the first report showing the size selective hydrogenation of olefins promoted by Cu@ZIF-8 (mixed-metal MOFs) compared to other noble metal nanoparticles (NPs) embedded over MOFs as catalysts.
- Nagarjun, Nagarathinam,Arthy, Kannan,Dhakshinamoorthy, Amarajothi
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p. 2108 - 2119
(2021/06/01)
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- Cu3(BTC)2 metal organic framework as heterogeneous solid catalyst for the reduction of styrenes with silane as reducing agent
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In this work, a well known metal organic framework, Cu3(BTC)2 (BTC: 1,3,5-benzenetricarboxylate) is reported as a heterogeneous solid catalyst for the reduction of styrene and its derivatives with silane as a reducing agent. Under these reaction conditions, a quantitative conversion of styrene is achieved with very high selectivity to ethylbenzene. A control experiment with pyridine as a catalyst poison revealed that Cu2+ located within the framework plays a crucial role in promoting this reduction. Further, hot-filtration test indicated the absence of metal leaching and Cu3(BTC)2 is used four times with no significant decay in its activity. In addition, the four times used Cu3(BTC)2 was compared with the fresh solid by powder X-ray diffraction, FT-IR, UV–Visible diffuse reflectance spectra, scanning electron microscope and electron paramagnetic resonance methods and observing no significant changes in its structural integrity, crystallinity and morphology. This process is extended for other styrene derivatives to their respective reduced products.
- Anbu, Nagaraj,Dhakshinamoorthy, Amarajothi
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- Transition-Metal- and Halogen-Free Oxidation of Benzylic sp 3 C-H Bonds to Carbonyl Groups Using Potassium Persulfate
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Aryl carbonyl compounds including acetophenones, benzophenones, imides, and benzoic acids are prepared from benzyl substrates using potassium persulfate as oxidant with catalytic pyridine in acetonitrile under mild conditions. Neither transition metals nor halogens are involved in the reactions.
- Hu, Yixin,Zhou, Lihong,Lu, Wenjun
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supporting information
p. 4007 - 4016
(2017/08/29)
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- Investigating the kinetics of homogeneous hydrogenation reactions using PHIP NMR spectroscopy
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The combination of parahydrogen induced polarization (PHIP), kinetics and NMR spectroscopy yields a powerful analytical tool: quantitative in situ NMR spectroscopy. Two versions of PHIP NMR experiments are presented to investigate the kinetics of homogeneously catalyzed hydrogenations. The first method, an experimental variation of the ROCHESTER experiment (ROCHESTER = rates of catalytic hydrogenation estimated spectroscopically through enhanced resonances), allows one to determine the hydrogenation rate independently of relaxation and other sources of decay, e.g., subsequent chemical reaction steps. The second method named DYPAS (dynamic PASADENA spectroscopy) uses a variable delay between the end of the hydrogen-addition period and the detection pulse. In principle, all processes during this delay can be described by a set of coupled differential equations. Their solutions can be fitted to the experimental data by a least-squares optimization of the involved kinetic parameters. The DYPAS method can be used to determine the rates of formation as well as the rates of decomposition of stable intermediates and has been applied to the case of freshly hydrogenated and still catalyst-attached product molecules. We provide kinetic data for the formation and decomposition of these unusual product-catalyst complexes during the hydrogenation of different styrene derivatives with a cationic Rh1 catalyst containing a chelating diphosphine ligand. The kinetic measurements indicate that the rate of formation of the catalyst-attached product increases whereas the rate constant of its decomposition diminishes if the para position of the arene ring of styrene carries an electron- donating substituent. In the case of p-aminostyrene as the substrate, the detachment step turned out to be rate limiting for the catalytic cycle. With certain substituted styrenes and cationic Rh1 complexes containing chiral chelating diphosphine ligands, two geometrically different (diastereomeric) product-catalyst adducts can be discriminated via PHIP NMR spectroscopy. The associated alternative reaction pathways have been analyzed by applying the DYPAS method, which can also be used to investigate the mechanism of an asymmetric hydrogenation.
- Hübler, Patrick,Giernoth, Ralf,Kümmerle, Günther,Bargon, Joachim
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p. 5311 - 5318
(2007/10/03)
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- A New Rearrangement of Alkoxybenzyl Anions
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Alkyl groups migrate from oxygen to carbon in alkyl aryl ethers which have been metalated in benzylic positions. 2,6-Dimethylanisole provides a variety of 2,6-dialkylphenols and their ethers in 45-80percent yields.Rearrangement products are obtained in 10-30percent yields from other dimethylanisoles and from methylanisoles.The reactions appear to proceed, like Wittig rearrangements, by homolytic cleavage of the alkyl-oxygen bond followed by recombination of the resulting radical pair in a different way.The rearrangements can be avoided by using methyl ethers and working at or below room temperature.
- Bates, Robert B.,Siahaan, Teruna J.,Suvannachut, Kessara
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p. 1328 - 1334
(2007/10/02)
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