- Vapor-Phase Cyclohexene Epoxidation by Single-Ion Fe(III) Sites in Metal-Organic Frameworks
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Heterogeneous catalysts supported on metal-organic frameworks (MOFs), which possess uniform porosity and crystallinity, have attracted significant interest for recent years due to the ease of active-site characterization via X-ray diffraction and the subs
- Otake, Ken-Ichi,Ahn, Sol,Knapp, Julia,Hupp, Joseph T.,Notestein, Justin M.,Farha, Omar K.
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- Cu(II)-amino acid–CaAl-layered double hydroxide complexes, recyclable, efficient catalysts in various oxidative transformations
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Intercalated composite materials were prepared with CaAl-layered double hydroxide as host and Cu(II)-amino acid (L-cysteine, L-histidine and L-tyrosine) complex anions as guests. Two methods (intercalation of the ligand first followed by constructing the complex; preforming the complex first, then introducing it among the layers of the host) and optimization of the synthesis conditions were performed to obtain composites having the complex exclusively among the layers. The composite materials were structurally characterized by powder X-ray diffractometry, mid infrared (IR) spectroscopy with ATR (attenuated total reflectance) or photoacoustic detections, transmission and scanning electron microscopies and X-ray photoelectron spectroscopy. Structural features of the intercalant (coordination number, coordination sites) were elucidated by classical chemical and energy dispersive X-ray analyses, EPR (electron paramagnetic spectroscopy), X-ray absorption and far IR spectroscopies. Structural models based on these methods are also given. Catalytic activities, selectivities and recycling abilities of the substances were studied in the oxidation reactions of cyclohexene with peracetic acid and in situ formed iodosylbenzene as oxidants in the liquid phase. The catalysts were active in the Ullmann coupling reaction as well. The intercalated substances were found to be efficient and highly selective catalysts with very good recycling abilities.
- Varga, Gábor,Ziegenheim, Szilveszter,Muráth, Szabolcs,Csendes, Zita,Kukovecz, ákos,Kónya, Zoltán,Carlson, Stefan,Korecz, László,Varga, Erika,Pusztai, Péter,Sipos, Pál,Pálinkó, István
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- A green route to 1,2-cyclohexanediol via the hydrolysis of cyclohexene oxide catalyzed by water
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Effective hydrolysis of cyclohexene oxide (CHO) was conducted by heating in water between 100 and 140 °C without another catalyst. It provided 100 % purity and 100 % yield of trans-1,2-cyclohexanediol (1,2-CHD) with five times of H2O to CHO at 120 °C for 6 h. These intermediates of polyether polyols could be totally decomposed to 1,2-CHD (monomer) by hot water under the same condition. The improved process eliminates the purification and markedly reduces the cost of 1,2-CHD in the follow-up industrial production. The main factors, such as reaction temperature, time, and water volume, were investigated. It was proposed that water acted as a modest acid catalyst, reactant, and solvent in the hydrolysis of CHO and polymers. Springer Science+Business Media B.V. 2012.
- Yang, Qiusheng,Yang, Xue,Wang, Yanji,Wang, Haiou,Cheng, Qingyan
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- Regioselective O2′,O3′-deacetylations of peracetylated ribonucleosides by using tetra-n-butylammonium fluoride
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A robust, mild, and highly regioselective deacetylation of 1,2-diol diacetates in the presence of other acetate functions was achieved by using tetra-n-butylammonium fluoride. This method provided a single-step route to access O5′-acetyl ribonucleosides, a key intermediate in the synthesis of biomedically important nucleosides and nucleotides. Moreover, it offered the general applicability of a non-enzymatic method for the selective deacetylation of peracetylated 2′-deoxyribonucleosides. Its synthetic utility was further demonstrated by the synthesis of molecules of biomedical interest by using this particular deacetylation reaction. Copyright
- Babu Kumar, Arun,Manetsch, Roman
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- Silica-Supported Titanium Derivatives as Catalysts for the Epoxidation of Alkenes with Hydrogen Peroxide: A New Way to Tuneable Catalytic Activity through Ligand Exchange
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Titanium tetraisopropoxide supported on silica [Si-Ti(OiPr)] is an efficient catalyst for the epoxidation of alkenes, cyclooctene, and cyclohexene with 30% hydrogen peroxide at 80°C. In the case of cyclohexene, allylic oxidation is also produced through a radical mechanism and the epoxide undergoes hydrolysis to the trans-diol due to the acidity of the catalyst and the presence of water. The catalyst can be recycled with very low titanium leaching and has a slightly lower catalytic activity after two cycles. These best results are obtained when an alkene/H2O2 ratio=20 is used. Lowering this ratio up to 5 has a detrimental effect on the final yield but does not affect the epoxidation/allylic selectivity. Further decrease to alkene/H2O2=1 leads to very low activity and selectivity. This catalyst bears isopropoxy groups that can be substituted by nonfunctionalized and functionalized diols. Such a process modifies the activity and selectivity of the catalyst, showing that it is possible to modulate the performance of this kind of titanium catalyst by changing the environment of the catalytic sites. The substitution with ethylene glycol improves the performance of the recovered catalyst. The catalyst prepared by treating the original Si-Ti(OiPr) with tartaric acid [Si-Ti(TA)] gives rise to high overall oxidation yields, with 97% selectivity in H2O2 and an epoxidation/allylic oxidation ratio around 65/35. Moreover, it is very stable during at least three cycles. End-capping of the silica surface has a positive effect on the epoxide hydrolysis but not on the epoxidation/allylic oxidation selectivity, in contrast with previously described results. The lower functionalization of the silylated solids noticeably increases the turnover numbers. Filtration experiments in the reaction conditions have shown that Si-Ti(OiPr) and Si(ec)-Ti(TA) are truly heterogeneous catalysts, with no contribution of the leached species. However, Si-Ti(TA) leads to leaching of active species, although an important part of them remains on the solid after three filtrations, and the contribution to the activity of homogeneous and heterogeneous species is nearly the same.
- Fraile, Jose M.,Garcia, Jose I.,Mayoral, Jose A.,Vispe, Eugenio
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- Supported sub-nanometer Ta oxide clusters as model catalysts for the selective epoxidation of cyclooctene
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The preparation of organic ligand-free, isolated tantalum oxide complexes (Ta1) and small clusters (Tan>1) on flat silicate supports was accomplished by ultra-high vacuum (UHV) techniques followed by oxidation in air. The resulting s
- Zwaschka,Rondelli,Krause,R?tzer,Hedhili,Heiz,Basset,Schweinberger,D'Elia
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- Is MCM-41 really advantageous over amorphous silica? The case of grafted titanium epoxidation catalysts
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MCM-41 can be used in the same way as amorphous silica for the preparation of supported titanium catalysts; MCM-41 does not show clear advantages over silica in epoxidation reactions with either TBHP or H2O2; only in one case is a positive effect observed and this involves the recycled catalyst with H2O2.
- Fraile,Garcia,Mayoral,Vispe,Brown,Naderi
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- Cyclohexene epoxidation with H2O2in the vapor and liquid phases over a vanadium-based metal-organic framework
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A metal-organic framework, MIL-47(V) containing coordinatively saturated V+IV sites linked together by terephthalic linkers, was prepared by a solvothermal method and evaluated as a catalyst in the epoxidation of cyclohexene. We have compared the catalytic activity in the condensed and gas phase oxidation of cyclohexene to discuss the effect of temperature and reaction phase in cyclohexene epoxidation over MIL-47(V). The catalysts were examined for the epoxidation of cyclohexene with H2O2 at 50, 65, 120, and 150 °C. We observed significant differences in product selectivity between liquid-phase and gas-phase operations and confirmed that the active sites are tightly incorporated into the MOF as node channels and thus resistant to leaching.
- Ahn, Sol,Bae, Youn-Sang,Farha, Omar K.,Kim, Ah-Reum,Notestein, Justin M.,Yoon, Tae-Ung
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- Synthesis of highly active tungsten-containing MCM-41 mesoporous molecular sieve catalyst
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A tungsten-containing MCM-41 mesoporous molecular sieve is synthesized by the hydrolysis of tetraethylorthosilicate and ammonium tungstate in the presence of cetylpyridinium bromide as template in acidic medium and found to be more active than the conventional WO3 catalyst in the hydroxylation of cyclohexene using H2O2 as oxidant.
- Zhang, Zhaorong,Suo, Jishuan,Zhang, Xiaoming,Li, Shuben
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- Highly efficient room-temperature oxidation of cyclohexene and d-glucose over nanogold Au/SiO2 in water
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Silica-supported nanogold catalysts suspended in 30% hydrogen peroxide using ultrasound are highly active and selective for cyclohexene and d-glucose oxidation at room temperature. In these conditions a polar reactant, D-glucose, can be efficiently and directly converted with 100% yield using this system, while a conversion of apolar cyclohexene is limited by the addition of a surfactant improving cosolubility in the system and/or catalyst/support wettability. To our best knowledge this is the first time that hydrogen peroxide has been used efficiently in association with a gold catalyst for the selective oxidation of cyclohexene in a biphasic system.
- Bujak, Piotr,Bartczak, Piotr,Polanski, Jaroslaw
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- Stable metal-organic framework-supported niobium catalysts
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Developing structurally well-defined, supported oxide catalysts remains a significant challenge. Here, we report the grafting of Nb(V) oxide sites onto the nodes of the Zr-based metal organic framework (MOF) NU-1000 as a stable, well-defined catalyst support. Nb(V) oxide was deposited with loadings up to 1.6 mmol/g via two postsynthetic methods: atomic layer deposition in a MOF, and solution-phase grafting in a MOF. Difference envelope density measurements indicated that the two synthetic methods resulted in different local structures of the Nb(V) ions within NU-1000. Despite their high Nb(V) loadings, which were equivalent to >60% surface coverage, nearly all Nb(V) sites of the MOF-supported catalysts were active sites for alkene epoxidation, as confirmed by phenylphosphonic acid titration. The MOF-supported catalysts were more selective than the control Nb-ZrO2 catalyst for cyclohexene epoxidation with aqueous H2O2 and were far more active on a gravimetric basis.
- Ahn, Sol,Thornburg, Nicholas E.,Li, Zhanyong,Wang, Timothy C.,Gallington, Leighanne C.,Chapman, Karena W.,Notestein, Justin M.,Hupp, Joseph T.,Farha, Omar K.
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- Mechanistic studies on the roles of the oxidant and hydrogen bonding in determining the selectivity in alkene oxidation in the presence of molybdenum catalysts
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When the molybdenum oxo(peroxo) acetylide complex [CpMo(O-O)(O)C≡CPh] is used as a catalyst for the oxidation of olefins, completely different product selectivity is obtained depending on the oxidant employed. When tert-butyl hydroperoxide (TBHP, 5.5 M) in dodecane is used as the oxidant for the oxidation of cyclohexene, cyclohexene oxide is formed with high selectivity. However, when H2O2 is used as the oxidant, the corresponding cis-1,2-diol is formed as the major product. Calculations performed by using density functional theory revealed the nature of the different competing mechanisms operating during the catalysis process and also provided an insight into the influence of the oxidant and hydrogen bonding on the catalysis process. The mechanistic investigations can therefore serve as a guide in the design of molybdenum-based catalysts for the oxidation of olefins. Copyright
- Chandra, Prakash,Pandhare, Swati L.,Umbarkar, Shubhangi B.,Dongare, Mohan K.,Vanka, Kumar
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- A microwave-enhanced, lewis acid-catalyzed synthesis of 1,3-dioxolanes and oxazolines from epoxides
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A fast and highly regio- and stereoselective transformation of non-conventional β-lactam- b containing epoxides into the corresponding cyclic 1,3-dioxolanes and oxazolines is herein reported, using microwave irradiation as an efficient source of energy, in the presence of stoichiometric or catalytic amounts of Lewis acids, without an additional solvent. These cyclic compounds are the protected forms of diols and amino alcohols.
- Benfatti, Fides,Cardillo, Giuliana,Gentilucci, Luca,Tolomelli, Alessandra,Monari, Magda,Piccinelli, Fabio
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- Effect of the reaction conditions on the epoxidation of alkenes with hydrogen peroxide catalyzed by silica-supported titanium derivatives
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Silica-supported titanium catalysts are active in the epoxidation of cyclohexene with diluted hydrogen peroxide at 80°C. At low H2O2/Ti ratio the contribution of the direct mechanism of epoxidation is important, around 40% of the productive H2O2 conversion and 60% of the epoxidation reaction. However, the increase in H2O2/Ti ratio modifies these results. The contribution of the direct epoxidation to H2O2 conversion is reduced to 20-30%, whereas contribution to epoxidation is kept in the range 40-60%. Neither the silanization of the silica surface nor the substitution of the isopropoxy groups by tartaric acid improves the behavior of the solid in these conditions. However, the simultaneous variation in hydrophilic character of the surface and titanium environment increases the contribution of the direct epoxidation. In contrast, the increase in H2O2/Ti ratio reduces the epoxide hydrolysis. The catalysts lose some titanium after reaction, but in general they show higher stability than closely related solids. The activity for direct and radical contributions changes after recovering, showing the important change in nature of the catalytic sites, which are not easily regenerated by extensive washing with different solvents. In any case, with cyclooctene, an alkene that does not form radicals, the activity for direct epoxidation shows a decline in every recycling but final turnover numbers are similar in the first three runs, showing high stability of the titanium on the solid.
- Fraile, Jose M.,Garcia, Jose I.,Mayoral, Jose A.,Vispe, Eugenio
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- Preparation and Catalytic Application of Transition Metal (Fe, V, or Cu) Oxides Homogeneously Dispersed in the Wall of Mesoporous Nb2O 5
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Fe, V, or Cu oxide was mixed in mesoporous Nb2O5, at a few atom percent, and their extremely high dispersion was confirmed by elemental analysis in about 5-nm spots using TEM-EDS. These mesoporous Nb 2O5 showed characteristic selectivity for cyclohexene oxidation depending on the kind of the doped metal oxide.
- Yamashita, Tomohiro,Lu, Daling,Kondo, Junko N.,Hara, Michikazu,Domen, Kazunari
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- A method for preparation of cycloalkane diols
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The present invention provides a process for preparing cycloalkane diols. In detail, the process for preparing cycloalkane diols of the present invention comprises contacting a gaseous oxidizer and cycloalkene with MIL metal - organic frameworks to produce cycloalkane diols.
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Paragraph 0058-0083
(2021/06/09)
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- Photo-Induced Dihydroxylation of Alkenes with Diacetyl, Oxygen, and Water
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Herein reported is a photo-induced production of vicinal diols from alkenes under mild reaction conditions. The present dihydroxylation method using diacetyl (= butane-2,3-dione), oxygen, and water dispenses with toxic reagents and intractable waste generation.
- Masuda, Yusuke,Ikeshita, Daichi,Murakami, Masahiro
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- Demonstrating the Critical Role of Solvation in Supported Ti and Nb Epoxidation Catalysts via Vapor-Phase Kinetics
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Catalytic oxidation of hydrocarbons with hydrogen peroxide (H2O2) has been of the utmost importance for several decades. The vast majority of studies have been performed in the condensed phase, even though condensed phases introduce complex solvent effects and can promote the leaching of active sites. In response, we have built a custom reactor system to understand H2O2 activation and selective oxidation in the vapor-phase. In this report, we study the epoxidation of cyclohexene with H2O2 over four Lewis-acidic metal oxide catalysts: Ti and Nb grafted on SiO2 and on the Zr based metal-organic framework, NU-1000. The M-SiO2 materials are highly selective to the formation of epoxides and diols, as they can be in the condensed phase, while the NU-1000 based materials are far more prone to overoxidation to CO2, which appears to be connected to their strong reactant adsorption. Apparent activation energies are calculated for all materials when operating in the same kinetic regime, and the heats of cyclohexene adsorption into their pores are then used to directly compare intrinsic enthalpies of activation in the vapor vs condensed phase for the M-SiO2 catalysts. Nb-SiO2 catalysts exhibit similar intrinsic enthalpies of activation in the vapor and condensed phases, whereas the condensed phase transition state in Ti-SiO2 is 24 kJ/mol lower in energy than that of the same material in the vapor phase. These experiments establish another methodology for understanding the various roles of solvent in selective oxidation reactions and studying these reactions under conditions that differ significantly from the thousands of prior studies in the condensed phase.
- Ahn, Sol,Ardagh, M. Alexander,Farha, Omar K.,Hicks, Kenton E.,Nauert, Scott L.,Notestein, Justin M.,Schweitzer, Neil M.
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p. 2817 - 2825
(2020/03/11)
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- The charge-assisted hydrogen-bonded organic framework (CAHOF) self-assembled from the conjugated acid of tetrakis(4-aminophenyl)methane and 2,6-naphthalenedisulfonate as a new class of recyclable Br?nsted acid catalysts
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The acid–base neutralization reaction of commercially available disodium 2,6-naphthalenedisulfonate (NDS, 2 equivalents) and the tetrahydrochloride salt of tetrakis(4-aminophenyl)methane (TAPM, 1 equivalent) in water gave a novel three-dimensional charge-assisted hydrogen-bonded framework (CAHOF, F-1). The framework F-1 was characterized by X-ray diffraction, TGA, elemental analysis, and 1H NMR spectroscopy. The framework was supported by hydrogen bonds between the sulfonate anions and the ammonium cations of NDS and protonated TAPM moieties, respectively. The CAHOF material functioned as a new type of catalytically active Br?nsted acid in a series of reactions, including the ring opening of epoxides by water and alcohols. A Diels–Alder reaction between cyclopentadiene and methyl vinyl ketone was also catalyzed by F-1 in heptane. Depending on the polarity of the solvent mixture, the CAHOF F-1 could function as a purely heterogeneous catalyst or partly dissociate, providing some dissolved F-1 as the real catalyst. In all cases, the catalyst could easily be recovered and recycled.
- Belokon, Yuri N.,Dmitrienko, Artem O.,Gak, Alexander S.,Gerasimov, Igor S.,Kuznetsova, Svetlana A.,Larionov, Vladimir A.,Li, Han,Medvedev, Michael G.,Nelyubina, Yulia V.,North, Michael,Saghyan, Ashot S.,Smol'yakov, Alexander F.,Zhereb, Vladimir P.
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supporting information
p. 1124 - 1134
(2020/07/10)
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- SYNTHESIS AND APPLICATION OF CHIRAL SUBSTITUTED POLYVINYLPYRROLIDINONES
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Chiral polyvinylpyrrolidinone (CSPVP), complexes of CSPVP with a core species, such as a metallic nanocluster catalyst, and enantioselective oxidation reactions utilizing such complexes are disclosed. The CSPVP complexes can be used in asymmetric oxidation of diols, enantioselective oxidation of alkenes, and carbon-carbon bond forming reactions, for example. The CSPVP can also be complexed with biomolecules such as proteins, DNA, and RNA, and used as nanocarriers for siRNA or dsRNA delivery.
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Paragraph 0046; 0047; 0049
(2020/11/24)
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- Olefin reaction in the catalyst and the olefin production
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PROBLEM TO BE SOLVED: To provide a catalyst for obtaining an olefin in high selectivity with a vicinal diol as a raw material.SOLUTION: A catalyst for olefination reaction for use in a reaction to produce an olefin by a reaction of a polyol, having two adjacent carbon atoms each having a hydroxy group, with hydrogen comprises: a carrier; at least one oxide selected from the group consisting of oxides of the group 6 elements and oxides of the group 7 elements supported on the carrier; and at least one metal selected from the group consisting of silver, iridium, and gold supported on the carrier.SELECTED DRAWING: None
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Paragraph 0147; 0149
(2020/10/31)
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- Enantiotopic Discrimination by Coordination-Desymmetrized meso-Ligands
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The first examples of enantiopure catalysts that are chiral merely due to coordination of different metal ions at enantiotopic positions of an achiral meso-ligand are reported. These catalysts exhibit a pseudo-Cs symmetry and are able to catalyze reactions demanding simultaneous involvement of two catalytic sites. The latter was demonstrated by application in the asymmetric ring-opening of meso-epoxides.
- Li, Yutang,Lidskog, Anna,Armengol-Relats, Helena,Pham, Thanh Huong,Favraud, Antoine,Nicolas, Maxime,Dawaigher, Sami,Xiao, Zeyun,Ma, Dayou,Lindb?ck, Emil,Strand, Daniel,W?rnmark, Kenneth
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p. 1575 - 1579
(2020/02/04)
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- Epoxidation of cyclohexene with H2O2 over efficient water-tolerant heterogeneous catalysts composed of mono-substituted phosphotungstic acid on co-functionalized SBA-15
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A series of Keggin-type heteropolyacid-based heterogeneous catalysts (Co-/Fe-/Cu-POM-octyl-NH3-SBA-15) were synthesized via immobilized transition metal mono- substituted phosphotungstic acids (Co-/Fe-/Cu-POM) on octyl-amino-co-functionalized mesoporous silica SBA-15 (octyl-NH2-SBA-15). Characterization results indicated that Co-/Fe-/Cu-POM units were highly dispersed in mesochannels of SBA-15, and both types of Br?nsted and Lewis acid sites existed in Co-/Fe-/Cu-POM-octyl-NH3-SBA-15 catalysts. Co-POM-octyl-NH3-SBA-15 catalyst showed excellent catalytic performance in H2O2-mediated cyclohexene epoxidation with 83.8% of cyclohexene conversion, 92.8% of cyclohexene oxide selectivity, and 98/2 of epoxidation/allylic oxidation selectivity. The order of catalytic activity was Co-POM-octyl-NH3-SBA-15?>?Fe-POM-octyl-NH3-SBA-15?>?Cu-POM-octyl-NH3-SBA-15. In order to obtain insights into the role of -octyl moieties during catalysis, an octyl-free catalyst (Co-POM-NH3-SBA-15) was also synthesized. In comparison with Co-POM-NH3-SBA-15, Co-POM-octyl-NH3-SBA-15 showed enhanced catalytic properties (viz. activity and selectivity) in cyclohexene epoxidation. Strong chemical bonding between -NH3 + anchored on the surface of SBA-15 and heteropolyanions resulted in excellent stability of Co-POM-octyl-NH3-SBA-15 catalyst, and it could be reused six times without considerable loss of activity.
- Jin, Manman,Niu, Qingtao,Guo, Zhenmei,Lv, Zhiguo
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- Well-confined polyoxometalate-ionic liquid in silicic framework for environmentally friendly asymmetric di-hydroxylation of olefins
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Chiral 1,2-diols with a high yield could be directly prepared from asymmetric di-hydroxylation of olefins via an eco-friendly and enduring catalyst, in which abundant "chiral pools" of polyoxometalate-ionic liquid were target-designed into the silicic framework (POM-ILS) and well stabilized in aqueous media.
- Liang, Dong,Wang, Yan,Wang, Sifan,Song, Chengkun,Shi, Yonghe,Liu, Qinghao,Zhu, Hailin,Li, Xia,Liu, Laishuan,Zhu, Na
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p. 6102 - 6106
(2019/03/12)
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- Organic salts and merrifield resin supported [PM12O40]3? (M = Mo or W) as catalysts for adipic acid synthesis
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Adipic acid (AA) was obtained by catalyzed oxidation of cyclohexene, epoxycyclohexane, or cyclohexanediol under organic solvent-free conditions using aqueous hydrogen peroxide (30%) as an oxidizing agent and molybdenum- or tungsten-based Keggin polyoxometalates (POMs) surrounded by organic cations or ionically supported on functionalized Merrifield resins. Operating under these environmentally friendly, greener conditions and with low catalyst loading (0.025% for the molecular salts and 0.001–0.007% for the supported POMs), AA could be produced in interesting yields.
- Pisk, Jana,Agustin, Dominique,Poli, Rinaldo
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- Aromatic Donor-Acceptor Interaction-Based Co(III)-salen Self-Assemblies and Their Applications in Asymmetric Ring Opening of Epoxides
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Aromatic donor-acceptor interaction as the driving force to assemble cooperative catalysts is described. Pyrene/naphthalenediimide functionalized Co(III)-salen complexes self-assembled into bimetallic catalysts through aromatic donor-acceptor interactions and showed high catalytic activity and selectivity in the asymmetric ring opening of various epoxides. Control experiments, nuclear magnetic resonance (NMR) spectroscopy titrations, mass spectrometry measurement, and X-ray crystal structure analysis confirmed that the catalysts assembled based on the aromatic donor-acceptor interaction, which can be a valuable noncovalent interaction in supramolecular catalyst development.
- Liang, Jian,Soucie, Luke N.,Blechschmidt, Daniel R.,Yoder, Aaron,Gustafson, Addie,Liu, Yu
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supporting information
p. 513 - 518
(2019/01/14)
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- Preparation of Highly Active Monometallic Rhenium Catalysts for Selective Synthesis of 1,4-Butanediol from 1,4-Anhydroerythritol
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1,4-Butanediol can be produced from 1,4-anhydroerythritol through the co-catalysis of monometallic mixed catalysts (ReOx/CeO2+ReOx/C) in the one-pot reduction with H2. The highest yield of 1,4-butanediol was over 80 %, which is similar to the value obtained over ReOx–Au/CeO2+ReOx/C catalysts. Mixed catalysts of CeO2+ReOx/C showed almost the same performance, giving 89 % yield of 1,4-butanediol. The reactivity trends of possible intermediates suggest that the reaction mechanism over ReOx/CeO2+ReOx/C is similar to that over ReOx–Au/CeO2+ReOx/C: deoxydehydration (DODH) of 1,4-anhydroerythritol to 2,5-dihydrofuran over ReOx species on the CeO2 support with the promotion of H2 activation by ReOx/C, isomerization of 2,5-dihydrofuran to 2,3-dihydrofuran catalyzed by ReOx on the C support, hydration of 2,3-dihydrofuran catalyzed by C, and hydrogenation to 1,4-butanediol catalyzed by ReOx/C. The reaction order of conversion of 1,4-anhydroerythritol with respect to H2 pressure is almost zero and this indicates that the rate-determining step is the formation of 2,5-dihydrofuran from the coordinated substrate with reduced Re in the DODH step. The activity of ReOx/CeO2+ReOx/C is higher than that of ReOx–Au/CeO2+ReOx/C, which is probably related to the reducibility of ReOx/C and the mobility of the Re species between the supports. High-valent Re species such as Re7+ on the CeO2 and C supports are mobile in the solvent; however, low-valent Re species, including metallic Re species, have much lower mobility. Metallic Re and cationic low-valent Re species with high reducibility and low mobility can be present on the carbon support as a trigger for H2 activation and promoter of the reduction of Re species on CeO2. The presence of noble metals such as Au can enhance the reducibility through the activation of H2 molecules on the noble metal and the formation of spilt-over hydrogen over noble metal/CeO2, as indicated by H2 temperature-programmed reduction. The higher reducibility of ReOx–Au/CeO2 lowers the DODH activity of ReOx–Au/CeO2+ReOx/C in comparison with ReOx/CeO2+ReOx/C by restricting the movement of Re species from C to CeO2.
- Wang, Tianmiao,Tamura, Masazumi,Nakagawa, Yoshinao,Tomishige, Keiichi
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p. 3615 - 3626
(2019/07/15)
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- Controlling Selectivity in Alkene Oxidation: Anion Driven Epoxidation or Dihydroxylation Catalysed by [Iron(III)(Pyridine-Containing Ligand)] Complexes
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A highly reactive and selective catalytic system comprising Fe(III) and macrocyclic pyridine-containing ligands (Pc-L) for alkene oxidation by using hydrogen peroxide is reported herein. Four new stable iron(III) complexes have been isolated and characterized. Importantly, depending on the anion of the iron(III) metal complex employed as catalyst, a completely reversed selectivity was observed. When X=OTf, a selective dihydroxylation reaction took place. On the other hand, employing X=Cl resulted in the epoxide as the major product. The reaction proved to be quite general, tolerating aromatic and aliphatic alkenes as well as internal or terminal double bonds and both epoxides and diol products were obtained in good yields with good to excellent selectivities (up to 93 % isolated yield and d.r.=99 : 1). The catalytic system proved its robustness by performing several catalytic cycles, without observing catalyst deactivation. The use of acetone as a solvent and hydrogen peroxide as terminal oxidant renders this catalytic system appealing.
- Tseberlidis, Giorgio,Demonti, Luca,Pirovano, Valentina,Scavini, Marco,Cappelli, Serena,Rizzato, Silvia,Vicente, Rubén,Caselli, Alessandro
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p. 4907 - 4915
(2019/08/30)
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- One-Pot Enzymatic Synthesis of Cyclic Vicinal Diols from Aliphatic Dialdehydes via Intramolecular C?C Bond Formation and Carbonyl Reduction Using Pyruvate Decarboxylases and Alcohol Dehydrogenases
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An enzymatic cascade reaction was developed for one-pot enantioselective conversion of aliphatic dialdehydes to chiral vicinal diols using pyruvate decarboxylases (PDCs) and alcohol dehydrogenases (ADHs). The PDCs showed promiscuity in catalysing the cyclization of aliphatic dialdehydes through intramolecular stereoselective carbon-carbon bond formation. Consequently, 1,2-cyclopentanediols in three different stereoisomeric forms and 1,2-cyclohexanediols in two different stereoisomeric forms could be prepared with high conversion and stereoisomeric ratio from the respective initial substrates, glutaraldehyde and adipaldehyde. These cascade reactions represent a promising approach to the biocatalytic synthesis of important chiral vicinal diols. (Figure presented.).
- Zhang, Yan,Yao, Peiyuan,Cui, Yunfeng,Wu, Qiaqing,Zhu, Dunming
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supporting information
p. 4191 - 4196
(2018/09/25)
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- Structural and Computational Insight into the Catalytic Mechanism of Limonene Epoxide Hydrolase Mutants in Stereoselective Transformations
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Directed evolution of limonene epoxide hydrolase (LEH), which catalyzes the hydrolytic desymmetrization reactions of cyclopentene oxide and cyclohexene oxide, results in (R,R)- and (S,S)-selective mutants. Their crystal structures combined with extensive theoretical computations shed light on the mechanistic intricacies of this widely used enzyme. From the computed activation energies of various pathways, we discover the underlying stereochemistry for favorable reactions. Surprisingly, some of the most enantioselective mutants that rapidly convert cyclohexene oxide do not catalyze the analogous transformation of the structurally similar cyclopentene oxide, as shown by additional X-ray structures of the variants harboring this slightly smaller substrate. We explain this puzzling observation on the basis of computational calculations which reveal a disrupted alignment between nucleophilic water and cyclopentene oxide due to the pronounced flexibility of the binding pocket. In contrast, in the stereoselective reactions of cyclohexene oxide, reactive conformations are easily reached. The unique combination of structural and computational data allows insight into mechanistic details of this epoxide hydrolase and provides guidance for future protein engineering in reactions of structurally different substrates.
- Sun, Zhoutong,Wu, Lian,Bocola, Marco,Chan, H. C. Stephen,Lonsdale, Richard,Kong, Xu-Dong,Yuan, Shuguang,Zhou, Jiahai,Reetz, Manfred T.
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p. 310 - 318
(2018/01/17)
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- Calix[8]arene as New Platform for Cobalt-Salen Complexes Immobilization and Use in Hydrolytic Kinetic Resolution of Epoxides
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Eight cobalt-salen complexes have been covalently attached to a calix[8]arene platform through a flexible linker by a procedure employing Click chemistry. The corresponding well-defined catalyst proved its efficiency in the hydrolytic kinetic resolution (HKR) of various epoxides through an operative bimetallic cooperative activation, demonstrating highly enhanced activity when compared to its monomeric analogue. As an insoluble complex, this multisite cobalt-salen catalyst could be easily recovered and reused in successive catalytic runs. Products were isolated by a simple filtration with virtually no cobalt traces and without requiring a prior purification by flash chromatography.
- Abdellah, Ibrahim,Martini, Cyril,Dos Santos, Amandine,Dragoe, Diana,Guérineau, Vincent,Huc, Vincent,Schulz, Emmanuelle
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p. 4761 - 4767
(2018/10/02)
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- Green Organocatalytic Dihydroxylation of Alkenes
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An inexpensive, green, metal-free one-pot procedure for the dihydroxylation of alkenes is described. H2O2 and 2,2,2-trifluoroacetophenone were employed as the oxidant and organocatalyst, respectively, in this highly sustainable protocol in which a variety of homoallylic alcohols, aminoalkenes, and simple alkenes were converted into the corresponding polyalcohols in good to excellent yields. This process takes advantage of an epoxidation reaction followed by an acidic treatment in which water participates in the ring opening of the in situ prepared epoxide to lead to the desired product.
- Theodorou, Alexis,Triandafillidi, Ierasia,Kokotos, Christoforos G.
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p. 1502 - 1509
(2017/04/01)
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- Towards a global greener process: from solvent-less synthesis of molybdenum(vi) ONO Schiff base complexes to catalyzed olefin epoxidation under organic-solvent-free conditions
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Nine Schiff base ligands derived from o-hydroxyaldehydes (2-hydroxybenzaldehyde, 2-hydroxy-3-methoxybenzaldehyde, 2-hydroxy- 1-naphthaldehyde) and nine corresponding dioxomolybdenum(vi) complexes, cis-[MoO2L(CH3OH)] or cis-[MoO2L(CH3OH)]·CH3OH and dinuclear [MoO2L]2, have been prepared using the conventional solution-based method as well as mechanochemically, by liquid assisted grinding (LAG). All products have been characterised by means of IR spectroscopy, thermal analyses and also by powder and five molybdenum complexes by single crystal X-ray diffraction. The crystal structure analysis of mononuclear complexes reveal distorted octahedral Mo(vi) coordination by ONO donor atoms from a dianionic tridentate Schiff base ligand, two oxido oxygen atoms from the MoO22+ moiety and an oxygen atom from the MeOH molecule trans to the oxido oxygen atom. Due to the trans effect of the oxido oxygen atom, Mo-O(MeOH) is the longest bond distance within the Mo coordination sphere and it expected to be the point of maximum reactivity of the complexes. All complexes have been studied as pre(catalysts) for the epoxidation of cis-cyclooctene, cyclohexene and (R)-limonene using aqueous tert-butyl peroxide (TBHP) as the oxidant and in the absence of an organic solvent.
- Cindri?, Marina,Pavlovi?, Gordana,Katava, Robert,Agustin, Dominique
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p. 594 - 602
(2017/02/05)
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- Hydrogen Bonding-Assisted Enhancement of the Reaction Rate and Selectivity in the Kinetic Resolution of d,l-1,2-Diols with Chiral Nucleophilic Catalysts
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An extremely efficient acylative kinetic resolution of d,l-1,2-diols in the presence of only 0.5 mol% of binaphthyl-based chiral N,N-4-dimethylaminopyridine was developed (selectivity factor of up to 180). Several key experiments revealed that hydrogen bonding between the tert-alcohol unit(s) of the catalyst and the 1,2-diol unit of the substrate is critical for accelerating the rate of monoacylation and achieving high enantioselectivity. This catalytic system can be applied to a wide range of substrates involving racemic acyclic and cyclic 1,2-diols with high selectivity factors. The kinetic resolution of d,l-hydrobenzoin and trans-1,2-cyclohexanediol on a multigram scale (10 g) also proceeded with high selectivity and under moderate reaction conditions: (i) very low catalyst loading (0.1 mol%); (ii) an easily achievable low reaction temperature (0 °C); (iii) high substrate concentration (1.0 M); and (iv) short reaction time (30 min). (Figure presented.).
- Fujii, Kazuki,Mitsudo, Koichi,Mandai, Hiroki,Suga, Seiji
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supporting information
p. 2778 - 2788
(2017/08/23)
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- Synthesis of titanium containing MCM-41 from industrial hexafluorosilicic acid as epoxidation catalyst
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The industrial by-product hexafluorosilicic acid was investigated as silicate source for titanium containing MCM-41 (Si/Ti–MCM-41) synthesis. An extended and detailed study, which includes the effects of several factors such as the state and content of Ti, surfactant/Si ratio and template removal technique on the physicochemical properties and catalytic activity of Si/Ti–MCM-41, is presented; The Si/Ti–MCM-41 was also characterized by powder X-ray diffraction, N2 adsorption-desorption, fourier transform infrared spectroscopy, ultraviolet-visible spectrophotometer, thermal gravimetric measurements, X-ray fluorescence and scanning electron microscopy. The results show that the specific surface area and pore volume of the molecular sieve reach 1040 m2 g?1 and 0.74 cm3 g?1 under the hydrothermal conditions of the Si/Ti mole ratio equal to 60, CTAB/Si mole ratio to 0.81, hydrothermal temperature at 343 K and time for 3 h. The catalytic performance shows that samples have higher activity and selectivity for cyclohexene epoxidation to produce cyclohexene oxide. With the reaction temperature 333 K and mole ratio of cyclohexene/tertiary butyl peroxide hydrogen equal to 1, the highest cyclohexene conversion and epoxide selectivity is 79.23% and 95%, respectively. The catalyst activity has not obvious change with two times recycles.
- Liu, Tieliang,Jin, Fang,Wang, Xianqiao,Fan, Yangchun,Yuan, Ming
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p. 316 - 323
(2017/09/30)
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- Micro reaction device reverse 1, 2-cyclohexanediol method
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The invention discloses a micro reaction device reverse 1, 2-cyclohexanediol method, the method mixes oxidation of hydrogen aqueous solution and formic acid, results in epoxy reagent, then reacts in sequence with cyclohexene and caustic soda solution in a micro reactor of a micro reaction device, the solution works without any catalyst in the reaction process, compared with available technologies, the method works without the intermediate cyclohexene oxide and catalyst, the production rate of the product obtained is high, the by-product is reduced, the 1, 2-cyclohexanediol can be applied in serialized and automated production.
- -
-
Paragraph 0010; 0023-0039
(2017/04/03)
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- Oxidation of Cyclohexene in the Presence of Transition-Metal-Substituted Phosphotungstates and Hydrogen Peroxide: Catalysis and Reaction Pathways
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Homogeneous catalytic oxidations of cyclohexene by transition-metal-substituted phosphotungstates [PW11M(L)O39]m? (PW11M, M=CoII, CuII, FeIII, NiII, MnII, L=H2O or absence) with hydrogen peroxide in acetonitrile were experimentally studied. The catalytic activities of allylic oxidation were found to strongly depend on the transition metals, and PW11Co showed the highest activity. The product distribution and the catalyst stability were dominated by mole ratio of hydrogen peroxide to PW11M, whereby low or high mole ratios led to stable structure of PW11M and predominant formation of allylic oxidation products or decomposition of PW11M, respectively. Different from the activation of the allylic C?H bond by radicals, the oxidation of C=C double bond was based on tungsten-peroxo species. A reaction mechanism composed of radical and nonradical processes was proposed from NMR, EPR, and kinetic data, to describe the reaction pathways of cyclohexene oxidation.
- Song, Yuexiao,Xin, Feng,Zhang, Lexiang,Wang, Yong
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p. 4139 - 4147
(2017/11/15)
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- Design and preparation of a polymer resin-supported organoselenium catalyst with industrial potential
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Hexavalent Se? Yes! Selenium on polymers exhibits quite different properties compared to that in small molecules. Hexavalent Se, rare in organoselenium chemistry, was found to be the major species on polymers. The high-valent Se species on recyclable polymer resins could quickly catalyze the oxidation reaction of cyclohexene with H2O2 in water to produce industrially important intermediate trans-1,2-cyclohexanediol in almost quantitative yield. In the catalytic cycle, high valent Se species were reduced to divalent Se, a highly activated species that could be re-oxidized by air so that no excess H2O2 was required for the reaction. The results were superior to those of reactions catalyzed by small molecules, for which excess H2O2, long reaction time or expensive CF3-activated catalysts and environmentally unfriendly MeCN solvent were required.
- Wang, Yuguang,Yu, Lihua,Zhu, Bingchun,Yu, Lei
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supporting information
p. 10828 - 10833
(2016/07/21)
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- A highly efficient protocol for regioselective ring-opening of epoxides with alcohols, water, acetic acid, and acetic anhydride catalyzed by SbF3
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SbF3as an efficient catalyst has been used for regioselective alcoholysis, acetolysis and hydrolysis of epoxides to the corresponding β-alkoxy, β-acetoxy alcohols, and 1,2-diols in high to excellent yields. This study also represents a convenient synthesis of vic-diacetates from ring-opening of epoxides with acetic anhydride.
- Zeynizadeh, Behzad,Gilanizadeh, Masumeh,Aminzadeh, Farkhondeh Mohammad
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p. 1051 - 1056
(2016/07/06)
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- OH-substituted tridentate ONO Schiff base ligands and related molybdenum(VI) complexes for solvent-free (ep)oxidation catalysis with TBHP as oxidant
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Molybdenum complexes with ONO tridentate Schiff base ligands based on salicylideneaminophenolato (SAP) backbone with OH substitution on the salicyl arene ring have been synthesized and characterized. The molecular structures of the full series of OH substituted molybdenum complexes were determined by X-ray crystallography as monomers stabilized by one solvent molecule, [MoO2L(D)]. All dimeric complexes [MoO2L]2 were tested for the epoxidation of cyclooctene and cyclohexene under organic solvent-free conditions using aqueous TBHP as oxidant. The position of the OH on the SAP-modified ligand influenced the catalytic activity of the respective complexes. DFT calculations for the catalytic cycle yield energy spans in agreement with the experimentally observed activity trend.
- Wang, Weili,Daran, Jean-Claude,Poli, Rinaldo,Agustin, Dominique
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p. 117 - 126
(2016/04/04)
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- Gold-Nanoparticle-Catalyzed Silaboration of Oxetanes and Unactivated Epoxides
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Supported gold nanoparticles catalyze the unprecedented insertion of a silylborane into the C-O bond of oxetanes and unactivated epoxides, forming γ- or β-silyloxy boronates in good to excellent yields. In the silaboration process the boron moiety is acting as a nucleophile and the silyl as an electrophile. No external additives or ligands are required, while the catalytic system is recyclable and reusable.
- Vasilikogiannaki, Eleni,Louka, Anastasia,Stratakis, Manolis
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p. 3895 - 3902
(2016/12/22)
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- Whole-Cell-Catalyzed Multiple Regio- and Stereoselective Functionalizations in Cascade Reactions Enabled by Directed Evolution
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Biocatalytic cascade reactions using isolated stereoselective enzymes or whole cells in one-pot processes lead to value-added chiral products in a single workup. The concept has been restricted mainly to starting materials and intermediate products that are accepted by the respective wild-type enzymes. In the present study, we exploited directed evolution as a means to create E. coli whole cells for regio- and stereoselective cascade sequences that are not possible using man-made catalysts. The approach is illustrated using P450-BM3 in combination with appropriate alcohol dehydrogenases as catalysts in either two-, three-, or four-step cascade reactions starting from cyclohexane, cyclohexanol, or cyclohexanone, respectively, leading to either (R,R)-, (S,S)-, or meso-cyclohexane-1,2-diol. The one-pot conversion of cyclohexane into (R)- or (S)-2-hydroxycyclohexanone in the absence of ADH is also described.
- Li, Aitao,Ilie, Adriana,Sun, Zhoutong,Lonsdale, Richard,Xu, Jian-He,Reetz, Manfred T.
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p. 12026 - 12029
(2016/11/16)
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- Chiral-Substituted Poly-N-vinylpyrrolidinones and Bimetallic Nanoclusters in Catalytic Asymmetric Oxidation Reactions
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A new class of poly-N-vinylpyrrolidinones containing an asymmetric center at C5 of the pyrrolidinone ring were synthesized from l-amino acids. The polymers, particularly 17, were used to stabilize nanoclusters such as Pd/Au for the catalytic asymmetric oxidations of 1,3- and 1,2-cycloalkanediols and alkenes, and Cu/Au was used for C-H oxidation of cycloalkanes. It was found that the bulkier the C5 substituent in the pyrrolidinone ring, the greater the optical yields produced. Both oxidative kinetic resolution of (±)-1,3- and 1,2-trans-cycloalkanediols and desymmetrization of meso cis-diols took place with 0.15 mol % Pd/Au (3:1)-17 under oxygen atmosphere in water to give excellent chemical and optical yields of (S)-hydroxy ketones. Various alkenes were oxidized with 0.5 mol % Pd/Au (3:1)-17 under 30 psi of oxygen in water to give the dihydroxylated products in >93% ee. Oxidation of (R)-limonene at 25 °C occurred at the C-1,2-cyclic alkene function yielding (1S,2R,4R)-dihydroxylimonene 49 in 92% yield. Importantly, cycloalkanes were oxidized with 1 mol % Cu/Au (3:1)-17 and 30% H2O2 in acetonitrile to afford chiral ketones in very good to excellent chemical and optical yields. Alkene function was not oxidized under the reaction conditions. Mechanisms were proposed for the oxidation reactions, and observed stereo- and regio-chemistry were summarized.
- Hao, Bo,Gunaratna, Medha J.,Zhang, Man,Weerasekara, Sahani,Seiwald, Sarah N.,Nguyen, Vu T.,Meier, Alex,Hua, Duy H.
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supporting information
p. 16839 - 16848
(2017/01/10)
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- Performance, Structure, and Mechanism of ReOx-Pd/CeO2 Catalyst for Simultaneous Removal of Vicinal OH Groups with H2
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The ceria-supported rhenium catalyst modified with palladium (ReOx-Pd/CeO2 (Re = 2 wt %, Pd/Re = 0.25)) is still the best catalyst for simultaneous hydrodeoxygenation. Higher Re loading amount decreased the activity. The simultaneous hydrodeoxygenation of cyclic vicinal diols occurs with high cis-stereoselectivity. ReOx-Pd/CeO2 catalysts were characterized by means of XRD, TEM, H2-TPR, XAFS, XPS, Raman, and DFT calculations. The Re species on ReOx-Pd/CeO2 (Re = 2 wt %, Pd/Re = 0.25) catalyst after reduction and after stoichiometric reaction of 1,2-hexanediol to 1-hexene were ReIV and ReVI, and the ReIV species were converted to ReVI through the stoichiometric reaction. The Re species on ReOx-Pd/CeO2 are proposed to be randomly located on the CeO2 surface, and probably only monomeric Re species have catalytic activity for simultaneous hydrodeoxygenation. This model can explain the higher activity of Re = 2 wt % catalyst than those of higher Re loading catalysts. The reaction is proposed to proceed by the tetra/hexavalent redox cycle of the Re center in the catalysis followed by hydrogenation.
- Ota, Nobuhiko,Tamura, Masazumi,Nakagawa, Yoshinao,Okumura, Kazu,Tomishige, Keiichi
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p. 3213 - 3226
(2016/07/06)
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- Uncovering Key Structural Features of an Enantioselective Peptide-Catalyzed Acylation Utilizing Advanced NMR Techniques
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We report on a detailed NMR spectroscopic study of the catalyst-substrate interaction of a highly enantioselective oligopeptide catalyst that is used for the kinetic resolution of trans-cycloalkane-1,2-diols via monoacylation. The extraordinary selectivity has been rationalized by molecular dynamics as well as density functional theory (DFT) computations. Herein we describe the conformational analysis of the organocatalyst studied by a combination of nuclear Overhauser effect (NOE) and residual dipolar coupling (RDC)-based methods that resulted in an ensemble of four final conformers. To corroborate the proposed mechanism, we also investigated the catalyst in mixtures with both trans-cyclohexane-1,2-diol enantiomers separately, using advanced NMR methods such as T1relaxation time and diffusion-ordered spectroscopy (DOSY) measurements to probe molecular aggregation. We determined intramolecular distance changes within the catalyst after diol addition from quantitative NOE data. Finally, we developed a pure shift EASY ROESY experiment using PSYCHE homodecoupling to directly observe intermolecular NOE contacts between the trans-1,2-diol and the cyclohexyl moiety of the catalyst hidden by spectral overlap in conventional spectra. All experimental NMR data support the results proposed by earlier computations including the proposed key role of dispersion interaction.
- Procházková, Eli?ka,Kolmer, Andreas,Ilgen, Julian,Schwab, Mira,Kaltschnee, Lukas,Fredersdorf, Maic,Schmidts, Volker,Wende, Raffael C.,Schreiner, Peter R.,Thiele, Christina M.
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supporting information
p. 15754 - 15759
(2016/12/16)
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- Comparing Different Strategies in Directed Evolution of Enzyme Stereoselectivity: Single- versus Double-Code Saturation Mutagenesis
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Saturation mutagenesis at sites lining the binding pockets of enzymes constitutes a viable protein engineering technique for enhancing or inverting stereoselectivity. Statistical analysis shows that oversampling in the screening step (the bottleneck) increases astronomically as the number of residues in the randomization site increases, which is the reason why reduced amino acid alphabets have been employed, in addition to splitting large sites into smaller ones. Limonene epoxide hydrolase (LEH) has previously served as the experimental platform in these methodological efforts, enabling comparisons between single-code saturation mutagenesis (SCSM) and triple-code saturation mutagenesis (TCSM); these employ either only one or three amino acids, respectively, as building blocks. In this study the comparative platform is extended by exploring the efficacy of double-code saturation mutagenesis (DCSM), in which the reduced amino acid alphabet consists of two members, chosen according to the principles of rational design on the basis of structural information. The hydrolytic desymmetrization of cyclohexene oxide is used as the model reaction, with formation of either (R,R)- or (S,S)-cyclohexane-1,2-diol. DCSM proves to be clearly superior to the likewise tested SCSM, affording both R,R- and S,S-selective mutants. These variants are also good catalysts in reactions of further substrates. Docking computations reveal the basis of enantioselectivity.
- Sun, Zhoutong,Lonsdale, Richard,Li, Guangyue,Reetz, Manfred T.
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p. 1865 - 1872
(2016/11/06)
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- Structure-Guided Triple-Code Saturation Mutagenesis: Efficient Tuning of the Stereoselectivity of an Epoxide Hydrolase
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The directed evolution of enzymes promises to eliminate the long-standing limitations of biocatalysis in organic chemistry and biotechnology - the often-observed limited substrate scope, insufficient activity, and poor regioselectivity or stereoselectivity. Saturation mutagenesis at sites lining the binding pocket with formation of focused libraries has emerged as the technique of choice, but choosing the optimal size of the randomization site and reduced amino acid alphabet for minimizing the labor-determining screening effort remains a challenge. Here, we introduce structure-guided triple-code saturation mutagenesis (TCSM) by encoding three rationally chosen amino acids as building blocks in the randomization of large multiresidue sites. In contrast to conventional NNK codon degeneracy encoding all 20 canonical amino acids and requiring the screening of more than 1015 transformants for 95% library coverage, TCSM requires only small libraries not exceeding 200-800 transformants in one library. The triple code utilizes structural (X-ray) and consensus-derived sequence data, and is therefore designed to match the steric and electrostatic characteristics of the particular enzyme. Using this approach, limonene epoxide hydrolase has been successfully engineered as stereoselective catalysts in the hydrolytic desymmetrization of meso-type epoxides with formation of either (R,R)- or (S,S)-configurated diols on an optional basis and kinetic resolution of chiral substrates. Crystal structures and docking computations support the source of notably enhanced and inverted enantioselectivity.
- Sun, Zhoutong,Lonsdale, Richard,Wu, Lian,Li, Guangyue,Li, Aitao,Wang, Jianbo,Zhou, Jiahai,Reetz, Manfred T.
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p. 1590 - 1597
(2016/03/15)
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- Multiparameter Optimization in Directed Evolution: Engineering Thermostability, Enantioselectivity, and Activity of an Epoxide Hydrolase
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The challenge of optimizing several parameters in the directed evolution of enzymes remains a central issue. In this study we address the thermostability, enantioselectivity, and activity of limonene epoxide hydrolase (LEH) as the catalyst in the hydrolytic desymmetrization of cyclohexene oxide with formation of (R,R)- and (S,S)-cyclohexane-1,2-diol. Wild type LEH shows a thermostability of T5030 = 41 °C and an enanioselectivity of 2% ee (S,S). Two approaches are described herein. In one strategy, the mutations generated previously by Janssen, Baker, and co-workers for notably increased thermostability are combined with mutations evolved earlier for enhanced enantioselectivity. Although highly enantioselective R,R and S,S variants (92-93% ee) with increases in T5030 by 10-11 °C were obtained, relative to wild type LEH the tradeoff in activity was significant. The second strategy based on the simultaneous optimization of both parameters using iterative saturation mutagenesis (ISM) with minimized tradeoff in activity proved to be superior. Several notably improved variants were observed, a reasonable "compromise" being R,R- and S,S-selective LEH variants (80-94% ee) showing enhanced thermostability by 5-10 °C and still reasonable levels of activity. Analysis of the X-ray structure of the S,S variant (94% ee) with and without diol product sheds light on the origin of altered stereoselectivity.
- Li, Guangyue,Zhang, Hui,Sun, Zhoutong,Liu, Xinqi,Reetz, Manfred T.
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p. 3679 - 3687
(2016/07/06)
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- Mixing and matching chiral cobalt- and manganese-based calix-salen catalysts for the asymmetric hydrolytic ring opening of epoxides
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Homochiral oligomeric salen macrocycles possessing aromatic spacers have been prepared as new calix-salen derivatives. The corresponding cobalt and manganese complexes were synthesized and characterized, and their catalytic activities have been studied in the challenging hydrolysis of meso epoxides. While manganese calix-salen complexes were not active in the studied reactions, the dual heterobimetallic system, using an equimolar combination of cobalt and manganese calix-salen derivatives proved to be more enantioselective than the sole cobalt system. Furthermore, as heterogeneous complexes, the catalytic mixture could be easily recovered by simple filtration and successfully reengaged in subsequent catalytic runs. Interestingly, no need for cobalt reactivation was noticed to maintain maximum efficiency of this dual system. The matched Co/Mn dual catalyst was also used to promote the dynamic hydrolytic kinetic resolution of epibromohydrin.
- Dandachi, Hiba,Zaborova, Elena,Kolodziej, Emilie,David, Olivier R.P.,Hannedouche, Jér?me,Mellah, Mohamed,Jaber, Nada,Schulz, Emmanuelle
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p. 246 - 253
(2017/03/01)
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- Selective transition-metal-free vicinal cis-dihydroxylation of saturated hydrocarbons
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A transition-metal-free cis-dihydroxylation of saturated hydrocarbons under ambient reaction conditions has been developed. The described approach allows a direct and selective synthesis of vicinal diols. The new reaction thereby proceeds via radical iodination and a sequence of oxidation steps. A broad scope of one-pot dual C(sp3)-H bond functionalization for the selective synthesis of vicinal syn-diols was demonstrated.
- Bering, Luis,Antonchick, Andrey P.
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p. 452 - 457
(2016/12/30)
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- Efficiency of Polyoxometalate-Based Mesoporous Hybrids as Covalently Anchored Catalysts
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Polyoxometalate (POM) hybrids have been covalently immobilized through the formation of amide bonds on several types of mesoporous silica. This work allows the comparison of three POM-based mesoporous systems, obtained with three different silica supports in which either the organic functions of the support (amine vs carboxylic acid) and/or the structure of the support itself (SBA-15 vs mesocellular foams (MCF)) were varied. The resulting POM-based mesoporous systems have been studied in particular by high resolution transmission electronic microscopy (HR-TEM) in order to characterize the nanostructuration of the POMs inside the pores/cells of the different materials. We thus have shown that the best distribution and loading in POMs have been reached with SBA-15 functionalized with aminopropyl groups. In this case, the formation of amide bonds in the materials has led to the nonaggregation of the POMs inside the channels of the SBA-15. The catalytic activity of the anchored systems has been evaluated through the epoxidation of cyclooctene and cyclohexene with H2O2 in acetonitrile. The reactivity of the different grafted POMs hybrids has been compared to that in solution (homogeneous conditions). Parallels can be drawn between the distribution of the POMs and the activity of the supported systems. Furthermore, recycling tests together with catalyst filtration experiments during the reaction allowed us to preclude the hypothesis of a significant leaching of the supported catalyst.
- Bentaleb, Faiza,Makrygenni, Ourania,Brouri, Dalil,Coelho Diogo, Cristina,Mehdi, Ahmad,Proust, Anna,Launay, Franck,Villanneau, Richard
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p. 7607 - 7616
(2015/08/11)
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- Functionality, Effectiveness, and Mechanistic Evaluation of a Multicatalyst-Promoted Reaction Sequence by Electrospray Ionization Mass Spectrometry
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A multicatalytic three-step reaction consisting of epoxidation, hydrolysis, and enantioselective monoacylation of cyclohexene was studied by using mass spectrometry (MS). The reaction sequence was carried out in a one-pot reaction using a multicatalyst. All reaction steps were thoroughly analyzed by electrospray ionization (ESI) MS (and MS/MS), as well as high-resolution MS for structure elucidation. These studies allow us to shed light on the individual mode of action of each catalytic moiety. Thus, we find that under the epoxidation conditions, the catalytically active N-methyl imidazole for the terminal acylation step is partially deactivated through oxidation. This observation helps to explain the lower efficiency of the catalyst in the last step compared to the monoacylation performed separately. All reactive intermediates and products of the reaction sequence, as well as of the side-reactions, were monitored, and we present a working mechanism of the reaction.
- Alachraf, M. Wasim,Wende, Raffael C.,Schuler, S?ren M. M.,Schreiner, Peter R.,Schrader, Wolfgang
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p. 16203 - 16208
(2015/11/03)
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- Direct transformation of epoxides to 1,2-diacetates with Ac2O/B(OH)3 system
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Direct transformation of different kinds of epoxides to 1,2-diacetates was carried out easily and efficiently with Ac2O/B(OH)3 system. All reactions were carried out under reflux conditions within 2 h to afford 1,2-diacetates in high yields.
- Gilanizadeh, Masumeh,Zeynizadeh, Behzad
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p. 1234 - 1238
(2016/01/12)
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- Silica microspheres containing high density surface hydroxyl groups as efficient epoxidation catalysts
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Uniformly sized silica microspheres were synthesized by a hydrolysis-condensation method. The obtained material was etched with a mild aqueous potassium hydroxide solution for different periods of time to break their Si-O-Si bonds and increases the density of hydroxyl groups on their surfaces. The resulting materials were then used as transition metal-free catalysts for oxidation of olefins in the presence of hydrogen peroxide as a green oxidant. The materials were thoroughly characterized using various physicochemical techniques. These highly populated hydroxyl groups on the surface of silica microspheres were proven to be responsible for excellent conversion (up to 93%) and epoxide selectivity (up to 100%) for various olefins. Quantum mechanical calculations also corroborate the experimental findings. Furthermore, both experimental and theoretical studies show that tertiary silanols were present at the active sites of the catalyst surface and were responsible for olefin epoxidation.
- Chandra, Prakash,Doke, Dhananjay S.,Umbarkar, Shubhangi B.,Vanka, Kumar,Biradar, Ankush V.
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p. 21125 - 21131
(2015/03/30)
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- A photoinduced cyclization cascade - Total synthesis of (-)-leuconoxine
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A protecting-group-free and enantioselective total synthesis of the monoterpenoid indole alkaloid (-)-leuconoxine was accomplished. The key step comprises a novel photoinduced domino macrocyclization/transannular cyclization involving the Witkop cyclization, for which additional mechanistic evidence is provided. This process furnishes a diaza[5.5.6.6]fenestrane skeleton, which is a hitherto unprecedented structure element.
- Pfaffenbach, Magnus,Gaich, Tanja
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p. 6355 - 6357
(2015/04/22)
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- Temperature-dependent immobilization of a tungsten peroxo complex that catalyzes the hydroxymethoxylation of olefins
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Abstract A tungsten peroxo complex stabilized by the bidentate picolinato ligand has been synthesized and then immobilized successfully on imidazole-functionalized silica. The immobilized tungsten-based catalyst was employed as an efficient catalyst for the one-pot synthesis of β-alkoxy alcohols from olefins and methanol with H2O2. Regarding the catalyst evaluation and the results of characterization by the various methods, it was demonstrated that the immobilization of tungsten peroxo complex was highly temperature-dependent. The tungsten peroxo complex can dissociate and diffuse into the liquid phase at reaction temperature, resulting in a homogeneous reaction. Nevertheless, the catalytically active species was anchored on the imidazole-functionalized silica by hydrogen bonding as the temperature was lowered to 0°C after the reaction, which thus offered a highly effective approach for recycling the catalyst for consecutive cycles. In addition, various olefins can be converted to the corresponding β-alkoxy alcohols with good conversion and selectivity under relative mild conditions by H2O2. Running hot and cold: A tungsten peroxo complex (see picture) can dissociate and diffuse into the liquid phase at the reaction temperature, resulting in a homogeneous reaction. After reaction, the catalytically active species was anchored on the functionalized silica by hydrogen-bonding as the temperature was lowered to 0°C. This offers an effective approach for catalyst recovery and recycling.
- Chen, Jizhong,Hua, Li,Chen, Chen,Guo, Li,Zhang, Ran,Chen, Angjun,Xiu, Yuhe,Liu, Xuerui,Hou, Zhenshan
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p. 1029 - 1037
(2015/06/08)
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- Periodic Trends in Highly Dispersed Groups IV and V Supported Metal Oxide Catalysts for Alkene Epoxidation with H2O2
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Supported metal oxides are important catalysts for selective oxidation processes like alkene epoxidation with H2O2. The reactivity of these catalysts is dependent on both identity and oxide structure. The dependence of the latter on the synthesis method can confound attempts at comparative studies across the periodic table. Here, SiO2-supported metal oxide catalysts of Ti(IV), Zr(IV), Hf(IV), V(V), Nb(V), and Ta(V) (all of groups IV and V) were synthesized by grafting a series of related calixarene coordination complexes at surface densities less than ~0.25 nm-2. Select catalysts were investigated by solid state NMR, UV-visible, and X-ray absorption near-edge spectroscopies. As-synthesized and calcined materials were examined for the epoxidation of cyclohexene and styrene (1.0 M) with H2O2 (0.10 M) at 45 and 65 °C. Nb catalysts emerge as high-performing materials, with calcined Nb-SiO2 proceeding at a cyclohexene turnover frequency of 2.4 min-1 (>2 times faster than Ti-SiO2) and with ~85% selectivity toward direct (nonradical) epoxidation pathways. As-synthesized Zr, Hf, and Ta catalysts have improved direct pathway selectivities compared with their calcined versions, particularly evident for Ta-SiO2. Finally, when the materials are synthesized from these precursors but not simple metal chlorides, the direct pathway reaction rate correlates with Pauling electronegativities of the metals, demonstrating clear periodic trends in intrinsic Lewis acid catalytic behavior.
- Thornburg, Nicholas E.,Thompson, Anthony B.,Notestein, Justin M.
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p. 5077 - 5088
(2015/09/15)
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- Alcohol cross-coupling for the kinetic resolution of diols via oxidative esterification
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We present an organocatalytic C-O-bond cross-coupling strategy to kinetically resolve racemic diols with aromatic and aliphatic alcohols, yielding enantioenriched esters. This one-pot protocol utilizes an oligopeptide multicatalyst, m-CPBA as the oxidant, and N,N-diisopropylcarbodiimide as the activating agent. Racemic acyclic diols as well as trans-cycloalkane-1,2-diols were kinetically resolved, achieving high selectivities and good yields for the products and recovered diols.
- Hofmann, Christine,Schümann, Jan M.,Schreiner, Peter R.
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p. 1972 - 1978
(2015/02/19)
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- The influences of Al species and Ti species on the catalytic epoxidation over Si/Ti-pillared MCM-36 synthesized from MCM-22
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A novel mesopore silica-aluminium material, i.e., Si/Ti-MCM-36 derivatives were prepared with Si/Ti mixed oxide as a pillar. The influences of acidity from Al species and the coordination state of Ti species on the catalytic cylcohexene epoxidation with t-butylhydroperoxide (TBHP) as the oxidant were investigated. The mesoporous structures were confirmed by XRD and N2 ads/desorption experiment. The acidity and surface polarity were characterized by NH3-TPD, 27Al 2D MQ MAS NMR and 29Si MAS NMR. The Ti coordination state was identified with UV-Vis spectra. By using 27Al 2D MQ MAS NMR technique, the Al species from the different eight crystallographically T (Si, Al) positions of MWW zeolite were identified, which are associated with bridging hydroxyl groups such as the Bronsted acid site. It was found that the Si/Ti-MCM-36 samples, whether with tetrahedrally (Td) or octahedrally (Oh) coordinated state Ti species, are all inactive for the cyclohexene epoxidation. A further acid treatment of the Si/Ti-MCM-36 samples can greatly expel Al species from the MWW structure, which largely decrease the acidity and transfer the acid-catalyzed decomposition of t-butylhydroperoxide to Ti catalyzed cyclohexene epoxidation. It shows that not only the amount of Al species but also their framework crystallographic positions have a great influence on the epoxidation activity. Furthermore, the grafting of the tetra-isopropoxide on the acid treated Si/Ti-MCM-36 can increase its hydrophobicity and epoxidation activity. Moreover, the Td TiO4 in the units has been confirmed to be the most active site for the epoxidation reaction.
- Jin, Fang,Huang, Shingjong,Cheng, Soofin,Wu, Yuanxin,Chang, Chih-Cheng,Huang, Yu-Wei
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p. 3007 - 3016
(2015/05/20)
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- Enantioselective Cascade Biocatalysis via Epoxide Hydrolysis and Alcohol Oxidation: One-Pot Synthesis of (R)-α-Hydroxy Ketones from Meso- or Racemic Epoxides
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A new type of cascade biocatalysis was developed for one-pot enantioselective conversion of a meso- or racemic epoxide to an α-hydroxy ketone in high ee via an epoxide hydrolase-catalyzed hydrolysis of the epoxide, an alcohol dehydrogenase-catalyzed oxidation of the diol intermediate, and an enzyme-catalyzed cofactor regeneration. In vitro cascade biotransformation of meso-epoxides (cyclopentene oxide 1a, cyclohexene oxide 1b, and cycloheptene oxide 1c) was achieved with cell-free extracts containing recombinant SpEH (epoxide hydrolase from Sphingomonas sp. HXN-200), BDHA (butanediol dehydrogenase from Bacillus subtilis BGSC1A1), and LDH (lactate dehydrogenase form Bacillus subtilis) or NOX (NADH oxidase from Lactobacillus brevis DSM 20054), respectively, giving the corresponding (R)-α-hydroxycyclopentanone 3a, (R)-α-hydroxycyclohexanone 3b, and (R)-α-hydroxycycloheptanone 3c in 98-99% ee and 70-50% conversion with TTN of NAD+-recycling of 5500-26000. Cascade catalysis with mixed cells of Escherichia coli (SpEH) and E. coli (BDHA-NOX) converted 100-300 mM meso-epoxides 1a-1c to (R)-α-hydroxy ketones 3a-3c in 98-99% ee and 85-57% conversion. Cells of E. coli (SpEH-BDHA-NOX) coexpressing all three enzymes were also proven as good catalysts for the cascade conversion of 100-200 mM meso-epoxides 1a-1c, giving (R)-α-hydroxy ketones 3a-3c in 98-99% ee and 79-52% conversion. The cascade biocatalysis for one-pot synthesis of α-hydroxy ketone in high ee was also successfully demonstrated with a racemic epoxide (1,2,3,4-tetrahydronaphthalene-1,2-oxide 1d) as the substrate. By using two whole-cells based approaches, (R)-α-hydroxytetralone 3d was obtained in 99% ee and 49-40% conversion from 20 to 5 mM racemic epoxide 1d. Preparative cascade biotransformation of cyclohexene oxide 1b gave (R)-α-hydroxycyclohexanone 3b in 98% ee with 70% isolated yield. The developed new type of cascade biocatalysis is enantioselective, green, and often high yielding. The concept might be generally applicable to produce other useful enantiopure α-hydroxy ketones from the corresponding meso- or racemic epoxides by cascade catalysis using appropriate enzymes. (Chemical Equation Presented).
- Zhang, Jiandong,Wu, Shuke,Wu, Jinchuan,Li, Zhi
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