286-20-4Relevant articles and documents
Synthesis, structure and catalytic activity of an oxo-bridged dinuclear oxovanadium complex of an isonicotinohydrazide ligand
Hosseini-Monfared, Hassan,Farrokhi, Afsaneh,Alavi, Sohaila,Mayer, Peter
, p. 267 - 273 (2013)
A mononuclear dioxo vanadium(V) complex of a hydrazone ONO donor ligand, [VVO2(L1)] (1), was synthesized by the reaction of V2O5 and terephthalic acid with H2L 1 in 1:1:1 mol ratio, while an oxo-bridged bis(vanadium(IV)oxo) complex, [μ 2-O-{VIVO(L2)}2] (2), was synthesized by the treatment of isonicotinic acid hydrazide, salicylaldehyde and CoSO4·7H2O with bis(acetylacetonato)oxovanadium(IV) (H2L1 = isonicotinic acid(2-hydroxy-benzylidene)-hydrazide, H2L2 = isonicotinic acid (1-methyl-3-oxo-butylidene)-hydrazide). The complexes were characterized by elemental analyses and spectroscopic methods. The crystal structure of complex 2 was determined by X-ray analysis. The complexes were tested as catalysts for the oxidation of cycloalkenes and benzyl alcohol using H 2O2 as terminal oxidant. Excellent selectivity was achieved in the oxidation of cyclohexene.
Epoxidation of cyclohexene with molecular oxygen by electrolysis combined with chemical catalysis
Wang, Yanlong,Deng, Jie,Zhang, Chao,Wu, Wenfeng,Xie, Qingji,Liu, Yachun,Fu, Zaihui
, p. 1723 - 1729 (2014)
This paper describes an electrochemical coupling epoxidation of cyclohexene by molecular oxygen (O2) under mild reaction conditions. Herein, the electroreduction of O2 to hydrogen peroxide (H2O2) efficiently proceeds in a relatively environmentally friendly acetone/water medium containing electrolytes at 25-30 °C on a self-assembled H type of electrolysis cell with tree electrodes system, providing ca. 44.3 mM concentration of H2O2 under the optimal electrolysis conditions. The epoxidation of cyclohexene with in situ generated H2O2 simultaneously occurs upon catalysis by metal complexes, giving ca. 19.8 % of cyclohexene conversion with 78 % of epoxidative selectivity over the best catalyst 5-Cl-7-I-8-quinolinolato manganese(III) complex (Q3MnIII (e)). The present electrochemical coupling epoxidation result is nearly equivalent to the epoxidation of cyclohexene with adscititious H2O2 catalyzed by the Q3MnIII (e).
New TiF4/SiO2 Catalysts for Liquid-phase Epoxidations with Aqueous H2O2
Jorda, E.,Tuel, A.,Teissier, R.,Kervennal, J.
, p. 1775 - 1776 (1995)
Ti-supported amorphous silica catalysts are prepared using a simple and original route with TiF4 and are very active in epoxidation reactions with aqueous hydrogen peroxide solutions.
The remarkable catalytic activity of the saturated metal organic framework V-MIL-47 in the cyclohexene oxidation
Leus, Karen,Muylaert, Ilke,Vandichel, Matthias,Marin, Guy B.,Waroquier, Michel,Van Speybroeck, Veronique,Van Der Voort, Pascal
, p. 5085 - 5087 (2010)
The remarkable catalytic activity of the saturated metal organic framework MIL-47 in the epoxidation of cyclohexene is elucidated by means of both experimental results and theoretical calculations. The Royal Society of Chemistry 2010.
Enhanced Catalysis Activity in a Coordinatively Unsaturated Cobalt-MOF Generated via Single-Crystal-to-Single-Crystal Dehydration
Ren, Hai-Yun,Yao, Ru-Xin,Zhang, Xian-Ming
, p. 6312 - 6318 (2015)
Hydrothermal reaction of Co(NO3)2 and terphenyl-3,2″,5″,3′-tetracarboxyate (H4tpta) generated Co3(OH)2 chains based 3D coordination framework Co3(OH)2(tpta)(H2O)4 (1) that suffered from single-crystal-to-single-crystal dehydration by heating at 160 °C and was transformed into dehydrated Co3(OH)2(tpta) (1a). During the dehydration course, the local coordination environment of part of the Co atoms was transformed from saturated octahedron to coordinatively unsaturated tetrahedron. Heterogenous catalytic experiments on allylic oxidation of cyclohexene show that dehydrated 1a has 6 times enhanced catalytic activity than as-synthesized 1 by using tert-butyl hydroperoxide (t-BuOOH) as oxidant. The activation energy for the oxidation of cylcohexene with 1a catalyst was 67.3 kJ/mol, far below the value with 1 catalysts, which clearly suggested that coordinatively unsaturated CoII sites in 1a have played a significant role in decreasing the activation energy. It is interestingly found that heterogeneous catalytic oxidation of cyclohexene in 1a not only gives the higher conversion of 73.6% but also shows very high selectivity toward 2-cyclohexene-1-one (ca. 64.9%), as evidenced in high turnover numbers (ca. 161) based on the open Co(II) sites of 1a catalyst. Further experiments with a radical trap indicate a radical chain mechanism. This work demonstrates that creativity of coordinatively unsaturated metal sites in MOFs could significantly enhance heterogeneous catalytic activity and selectivity. (Graph Presented).
Photocatalyzed oxidation of cyclohexene and cyclooctene with (nBU4N)4W10O32 and (nBu4N)4W10O32/Fe(III)[meso-tetrakis(2,6- dichlorophenyl)-porphyrin] in homogeneous and heterogeneous systems
Molinari,Amadelli,Carassiti,Maldotti
, p. 91 - 96 (2000)
Photoexcitation of (nBu4N)4W10O32 is a suitable mean of oxidizing cyclohexene and cyclooctene with O2 at room temperature and pressure. This process can be carried out in homogeneous solution as well as using the decatungstate in a dispersed form after its heterogenisation on silica. Cyclohexene and cyclooctene are mainly oxidized to the corresponding hydroperoxides as a consequence of primary photoprocesses which lead to the formation of allylic radicals. The presence of the Fe(III)[meso-tetrakis(2,6- dichlorophenyl)porphyrin] chloride as cocatalyst strongly affects the photocatalytic properties of (nBu4N)4W10O32, playing a key role in the allylic-hydroperoxide dependent oxidation of the cycloalkenes. In the photooxidation of cyclohexene, the porphyrin increases the photocatalytic efficiency of the decatungstate in terms of total turnover number and catalyses the decomposition of cyclohexenyl hydroperoxide with the selective formation of cyclohex-2-en1-ol. On the other hand, its presence during the photoinduced oxidation of cyclooctene favours the formation of cyclooctene epoxide by addition of ROO· and RO· radicals to the double bond. In the case of cyclooctene, the heterogenisation of the decatungstate on the solid support also affects the chemoselectivity of the photocatalytic process in the absence of the iron porphyrin complex.
Selective Catalytic Oxidation of Cyclohexene with Molecular Oxygen: Radical Versus Nonradical Pathways
Denekamp, Ilse M.,Antens, Martijn,Slot, Thierry K.,Rothenberg, Gadi
, p. 1035 - 1041 (2018)
We study the allylic oxidation of cyclohexene with O2 under mild conditions in the presence of transition-metal catalysts. The catalysts comprise nanometric metal oxide particles supported on porous N-doped carbons (M/N:C, M=V, Cr, Fe, Co, Ni, Cu, Nb, Mo, W). Most of these metal oxides give only moderate conversions, and the majority of the products are over-oxidation products. Co/N:C and Cu/N:C, however, give 70–80 % conversion and 40–50 % selectivity to the ketone product, cyclohexene-2-one. Control experiments in which we used free-radical scavengers show that the oxidation follows the expected free-radical pathway in almost all cases. Surprisingly, the catalytic cycle in the presence of Cu/N:C does not involve free-radical species in solution. Optimisation of this catalyst gives >85 % conversion with >60 % selectivity to the allylic ketone at 70 °C and 10 bar O2. We used SEM, X-ray photoelectron spectroscopy and XRD to show that the active particles have a cupric oxide/cuprous oxide core–shell structure, giving a high turnover frequency of approximately 1500 h?1. We attribute the high performance of this Cu/N:C catalyst to a facile surface reaction between adsorbed cyclohexenyl hydroperoxide molecules and activated oxygen species.
The coordinatively saturated vanadium MIL-47 as a low leaching heterogeneous catalyst in the oxidation of cyclohexene
Leus, Karen,Vandichel, Matthias,Liu, Ying-Ya,Muylaert, Ilke,Musschoot, Jan,Pyl, Steven,Vrielinck, Henk,Callens, Freddy,Marin, Guy B.,Detavernier, Christophe,Wiper, Paul V.,Khimyak, Yaroslav Z.,Waroquier, Michel,Van Speybroeck, Veronique,Van Der Voort, Pascal
, p. 196 - 207 (2012)
A Metal Organic Framework, containing coordinatively saturated V +IV sites linked together by terephthalic linkers (V-MIL-47), is evaluated as a catalyst in the epoxidation of cyclohexene. Different solvents and conditions are tested and compared. If the oxidant TBHP is dissolved in water, a significant leaching of V-species into the solution is observed, and also radical pathways are prominently operative leading to the formation of an adduct between the peroxide and cyclohexene. If, however, the oxidant is dissolved in decane, leaching is negligible and the structural integrity of the V-MIL-47 is maintained during successive runs. The selectivity toward the epoxide is very high in these circumstances. Extensive computational modeling is performed to show that several reaction cycles are possible. EPR and NMR measurements confirm that at least two parallel catalytic cycles are co-existing: one with V+IV sites and one with pre-oxidized V +V sites, and this is in complete agreement with the theoretical predictions.
Catalytic Behavior of Niobium(v)-Tetraphenylporphyrin in the Oxidation of Cyclohexene with Hydrogen Peroxide Evaluated by 1H NMR Spectroscopy
Kaiser, Carlos Roland,Abdel-Rehim, Mona A.,Machado, Mauro Cesar S.,Souza, Eduardo Lauande T.,Lachter, Elizabeth Roditi
, p. 708 - 709 (1998)
The catalytic efficiency of the niobium(v)-tetraphenylporphyrin complex in the oxidation reaction of cyclohexene with aqueous hydrogen peroxide was evaluated using 1H NMR spectroscopy.
Catalytic oxidation of hydrocarbons by trinuclear μ-oxo-bridged ruthenium-acetate clusters: Radical versus non-radical mechanisms
Nunes, Genebaldo S.,Alexiou, Anamaria D.P.,Toma, Henrique E.
, p. 188 - 192 (2008)
The [Ru3O(H3CCO2)6(py)2 (L)]PF6 clusters, where L = methanol or dimethyl sulfoxide, can be activated by peroxide or oxygen donor species, such as tert-butyl hydroperoxide (TBHP) or iodosylbenzene (PhIO), respectively, generating reactive intermediates of the type [RuIV,IV,III3{double bond, long}O]+. In this way, they catalyse the oxidation of cyclohexane or cyclohexene by TBHP and PhIO, via oxygen atom transfer, rather than by the alternative oxygen radical mechanism characteristic of this type of complexes. In addition to their ability to perform efficient olefin epoxydation catalysis, these clusters also promote the cleavage of the C{single bond}H bond in hydrocarbons, resembling the oxidation catalysis by metal porphyrins.
Tuning of the reaction parameters to optimize allylic oxidation of cyclohexene catalyzed by zeolite-Y entrapped transition metal complexes
Godhani, Dinesh R.,Nakum, Haresh D.,Parmar, Digvijaysinh K.,Mehta, Jignasu P.,Desai, Nisheeth C.
, p. 37 - 55 (2016)
The synthetic protocols for entrapment of transition metal complexes reported here are to expand the diversity in catalysis made possible by the ability of microporous solid to select reactants, transition states, and products based on their molecular size. Herein, we report a synthetic route for the entrapment of transition metal complexes within the nanopores of zeolite-Y. The complexes of transition metals [M = Fe(II), VO(IV)] with Schiff base ligands that are synthesized by simple condensation of 2-hydroxyacetophenone and/or 2-hydroxy-5-chloroacetophenone with ethylenediamine have been entrapped within nanopores of zeolite-Y by flexible ligand method. These materials have been characterized by various physicochemical and spectroscopic techniques such as ICP-OES, FT-IR, 1H and 13C NMR, elemental analyzes, and UV-vis electronic spectral studies, BET, TGA, scanning electron micrographs (SEMs), X-ray diffraction patterns (XRD), conductivity, magnetic susceptibilities as well as AAS. These synthesized catalysts have been utilized as heterogeneous catalysts for liquid phase oxidation of cyclohexene. The reaction parameters have been tuned to optimize higher cyclohexene conversion (%) along with higher selectivity towards the formation of corresponding allylic products. These catalysts were recovered and reused for three times without remarkable loss of activity. Moreover, the intermediate species involved during the catalytic oxidation reaction was synthesized and identified by FTIR and UV-vis spectroscopy.
A highly efficient heterogeneous catalyst of cobalt-based coordination polymers for aerobic epoxidation of cyclohexene
Yu, Fan
, p. 5074 - 5078 (2018)
A novel heterogeneous catalyst of cobalt-based coordination polymers has been successfully fabricated using a tyrosine-based derivative. Heterogeneous catalytic experiments on allylic oxidation of cyclohexene indicate that the titled complexes present high catalytic activities using tert-butyl hydroperoxide (t-BuOOH) as an oxidant. The activation energy for the whole process of oxidation of cyclohexene has been calculated to be 25.5 kJ mol-1, which indicates the important role of the selected ancillary ligands in the synthesis of the heterogeneous catalyst.
Ultrafast synthesis of nanosized Ti-Beta as an efficient oxidation catalyst: Via a structural reconstruction method
Wang, Bowen,Xu, Hao,Zhu, Zhiguo,Guan, Yejun,Wu, Peng
, p. 1857 - 1866 (2019)
As a representative selective oxidation titanosilicate catalyst, a Ti-Beta zeolite is less used in comparison with TS-1, Ti-MWW and Ti-MOR, mostly due to its high hydrophilicity originating from a BEA? intergrowth framework. A novel recrystallization method was proposed in the present study to prepare highly hydrophobic Ti-Beta with nanosized crystals (90 nm), high Ti content (Si/Ti = 20) and intercrystal mesoporosity. The fluoride-assisted recrystallization was realized quickly by dissolving extensively a dealuminated Beta zeolite in a mixture of a tetraethylammonium aqueous solution and Ti precursor, producing highly crystalline Ti-Beta in an extremely short time of 1 h. The obtained Ti-Beta zeolite exhibited superior catalytic activity in the liquid-phase epoxidation reactions of bulky alkenes like cyclohexene with hydrogen peroxide or tert-butyl hydroperoxide as an oxidant, compared to those Ti-Beta catalysts prepared by conventional hydrothermal or secondary synthesis routes.
A Bimetallic Pure Inorganic Framework for Highly Efficient and Selective Photocatalytic Oxidation of Cyclohexene to 2-Cyclohexen-1-ol
Shi, Xiaoyun,Shi, Zhuolin,Niu, Guiqin,Si, Chen,Han, Qiuxia,Zhang, Jingjing
, p. 3048 - 3057 (2019)
Abstract: The highly efficient and selective photocatalytic oxidation of cyclohexene with molecular oxygen under mild conditions is an important objective in chemical synthesis. In this work, a pure inorganic framework CoMo was self-assembly prepared under solvothermal conditions by incorporating simple MoO42?, cobalt (II) ion. The catalyst CoMo was well characterized by infrared spectroscopy (FTIR), nitrogen adsorption–desorption, powder X-ray diffraction (XRD), scanning electron spectroscopy (SEM), and X-ray photoelectron spectroscopy (XPS) methods. It displayed high efficiency and selectivity in the photocatalytic oxidation of cyclohexene to 2-cyclohexen-1-ol in O2 atmosphere. The influence of solvents, oxidants, pressure of oxygen, reaction temperature, light source and time on the reaction was investigated. More interestingly, the selectivity of the reaction in 4-ethyltoluene was much higher than that in other solvents. Graphic Abstract: [Figure not available: see fulltext.].
Magnetically recoverable copper oxide catalysts for aerobic allylic oxidation of cyclohexene
da Silva, Fernanda Parra,Gon?alves, Renato V.,Rossi, Liane M.
, p. 534 - 541 (2017)
Magnetically recoverable copper oxide catalysts prepared by sol-immobilization method exhibited interesting properties for the allylic oxidation of cyclohexene with molecular oxygen as the sole oxidant. The catalysts were prepared by immobilization of pre-synthesized PVA (polyvinyl alcohol)-stabilized Cu2O nanoparticles (NPs) on a magnetically recoverable support; the catalyst was further oxidized to CuO NPs after calcination at 600?°C. Both catalysts can selectively oxidize cyclohexene through allylic oxidation to give 2-cyclohexene-1-one as the main product, but CuO was identified as the most active species providing 90% cyclohexene conversion and 96% selectivity for allylic products under 100?°C and 4?bar pressure of O2 for 6?h of reaction time. The catalysts were magnetically recovered without metal leaching and could be reused in at least six consecutive runs.
Oxidation of cyclohexene with t-butyl hydroperoxide catalyzed by transition metal oxide clusters
Zhang, Cuiju,Ozawa, Yoshiki,Hayashi, Yoshihito,Isobe, Kiyoshi
, p. C21 - C26 (1989)
Organometallic oxide clusters (cp' = η5-C5Me5) and 2 catalyze the oxidation of cyclohexene with t-butyl hydroperoxide to give allylic oxidation products mainly and epoxycyclohexane selectively, respectively.
Efficient allylic oxidation of cyclohexene catalyzed by trimetallic hybrid nano-mixed oxide (Ru/Co/Ce)
Ghiaci, Mehran,Aghabarari, Behzad,Botelho Do Rego,Ferraria,Habibollahi, Saeed
, p. 225 - 230 (2011)
The paper deals with the reactivity of RuO2/Co3O 4/CeO2 nanoparticles prepared by a reverse micelle approach, which was precipitated by alkali-hydrolysis of RuCl3, Co(NO3)2 and Ce(NO3)2 and transformed into RuO2/Co3O4/CeO2 catalyst by calcinations in air at 400 °C. The catalysts were investigated with XRD, TEM, XPS, and BET techniques and were tested for oxidation of cyclohexene. The nano-catalyst exhibited high catalytic activities for the oxidation of cyclohexene to the corresponding α,β-unsaturated ketone under heterogeneous condition. In order to obtain maximum conversion of cyclohexene, the reaction parameters, like reaction temperature and time, were optimized. Under the optimized conditions, a maximum of 97.7% cyclohexene conversion and 95% selectivity, was achieved with RuO2/Co 3O4/CeO2 mixed oxide nano-catalyst.
Selective Oxidation of Cyclohexene with H2O2 Catalyzed by Resin Supported Peroxo Phosphotungstic Acid Under Mild Conditions
Liu, Jia,Yang, Guoqiang,Liu, Ying,Zhou, Zheng,Zhang, Zhibing,Hu, Xingbang
, p. 147 - 152 (2021)
Abstract: A series of modified chloromethyl polystyrene resins loaded with peroxo phosphotungstic acid catalysts were synthesized for the selective oxidation of cyclohexene. The surface of resin was enriched with high concentration quaternary ammonium salt, and grafted with a large amount of peroxo PW-anion through ion exchange. The novel resin catalyst showed excellent cyclohexene conversion and epoxide selectivity using 30% H2O2 as oxidant at ambient temperature. Furthermore, the resin catalyst exhibited excellent recycling stability, which can be reused by a simple filtration and the peroxo phosphotungstic acid did not leach into the solvent after reaction. Graphic Abstract: [Figure not available: see fulltext.]
Selective allylic oxidation of cyclohexene catalyzed by nitrogen-doped carbon nanotubes
Cao, Yonghai,Yu, Hao,Peng, Feng,Wang, Hongjuan
, p. 1617 - 1625 (2014)
Carbon nanotubes (CNTs) and nitrogen-doped CNTs (NCNTs) were systematically investigated as metal-free catalysts in the selective allylic oxidation of cyclohexene using molecular oxygen as oxidant in the liquid phase. High cyclohexene conversion (up to 59.0%) and 620.1 mmol g-1 h -1 mass-normalized activity were obtained for NCNTs, competing with the state-of-the-art metal catalysts. The positive effect of nitrogen dopant on the performance of CNTs was demonstrated, with respect to the aspects of enhancing activity and increasing selectivity of 2-cyclohexen-1-one, allowing for a ketone/alcohol ratio of 3.7 at 59% conversion. The unique catalytic role of NCNTs was attributed to their capability to promote the radical chain propagation via stabilizing peroxyl and cycloxyl radicals, which boosted the further conversion of 2-cyclohexen-1-ol toward 2-cyclohexen-1-one as well.
Heteropolytungstate nanoparticles: Microemulsion-mediated preparation and investigation of their catalytic activity in the epoxidation of olefins
Masteri-Farahani,Ghorbani
, p. 332 - 337 (2016)
Keggin type Q3PW12O40 nanoparticles (Q = cetyltrimethylammonium cation) were synthesized in water-in-oil (w/o) microemulsion consisted of water/cetyltrimethylammonium bromide/n-butanol/isooctane. Reaction of Na2WO4, Na2HPO4 and hydrochloric acid within water containing nanoreactors of reverse micelles resulted in the preparation of Q3PW12O40 nanoparticles. The resultant nanoparticles were analyzed by physicochemical methods such as FT-IR spectroscopy, X-ray diffraction, energy-dispersive X-ray analysis, thermogravimetric analyses (TGA-DTA), scanning and transmission electron microscopy and atomic force microscopy which show nearly uniform spherical nanoparticles with size of about 15 nm. Finally, catalytic activity of the Q3PW12O40 nanoparticles was examined in the epoxidation of olefins with H2O2. The prepared nanoparticles acted as recoverable and reusable catalyst in the epoxidation of olefins with H2O2.
(μ-O,O′)-nitrito bridged 3-D coordination frameworks of M2+ (Mn Co, Zn) with mab and jsm topology
Paul, Rima,Guha, Ankur K.,Saikia, Lakshi,Bora, Sanchay J.
, p. 42 - 49 (2017)
Four new nitrito-bridged coordination polymers of formulation [Zn(NO2)2(H2O)2]n (1) and [M(bipy)(NO2)2]n [M = Zn (2), Co (3), Mn (4)] were synthesized under solvothermal condition using N,N-dimethylformamide (DMF) as a reducing solvent. Theoretical calculation suggests in situ reduction of nitrate to nitrite with high spontaneity and without any thermodynamic barrier (ΔG = ?20.4?kcal/mol). All the complexes were characterized by elemental analysis, FT-IR spectroscopy, UV–vis spectroscopy, Raman Spectroscopy, TG analysis as well as by single crystal X-ray diffraction methods. TD-DFT approach has been employed to assign the electronic transitions occurring in the cobalt(II) complex (3) and were compared with those observed experimentally. This work also describes the preliminary studies on heterogeneous oxidation of cyclohexene by 2&3 in acetonitrile medium using TBHP.
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Noels et al.
, p. 79,81, 85 (1979)
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Magnetic properties and catalytic performance of iron-containing mesoporous molecular sieves
Elías, Verónica R.,Oliva, Marcos I.,Urreta, Silvia E.,Silvetti, Silvia P.,Sapag, Karim,Mudarra Navarro, Azucena M.,Casuscelli, Sandra G.,Eimer, Griselda A.
, p. 92 - 100 (2010)
Fe-containing mesoporous molecular sieves were synthesized by the wet impregnation method with two different metallic loadings. The resulting iron oxide/silica composites were then submitted to a reduction treatment for 6 h at 873 K, under H2 flow. The microstructure of both, the Si-MCM-41 host and the impregnated composites were characterized by XRD, N2 adsorption, DRUV-vis and M?ssbauer spectroscopy. The magnetic behavior of each microstructure was characterized by the magnetization dependence on the magnetic field (up to 1.5 T) and temperature (between 5 and 300 K). The catalytic performance was tested for cyclohexene oxidation by hydrogen peroxide and further correlated with the observed magnetic properties. It was found that the reduction treatment largely affects the selectivity to reaction products, leading to catalysts exhibiting a selectivity of 80% towards the allylic oxidation products. This is attributed to a large free radical generation arising from the interaction between the hydrogen peroxide and the partially reduced iron species (mainly Fe0 and Fe3O4), exhibiting superparamagnetic and/or ferromagnetic character.
Catalytic oxidation of cyclohexene by molecular oxygen over isopolyoxometalates
Liu, Yanyong,Murata, Kazuhisa,Inaba, Megumu,Nakajima, Hitoshi,Koya, Masahiko,Tomokuni, Keizou
, p. 200 - 201 (2004)
Isopolyoxomolybdates exhibited high selectivities for the industrially useful products (cyclohexene oxide and 2-cyclohexen-1-ol) catalyzing effectively the reaction of initial product cyclohexenyl hydroperoxide with cyclohexene in the oxidation of cyclohexene by molecular oxygen.
Kinetic Studies on the Oxoiron(IV) Complex with Tetradentate Aminopyridine Ligand PDP: Restoration of Catalytic Activity by Reduction with H2O2
Piquette, Marc C.,Kryatov, Sergiy V.,Rybak-Akimova, Elena V.
, (2019)
Oxoiron(IV) is a common catalytic byproduct observed in the oxidation of alkenes by the combination of H2O2 and nonheme iron catalysts including complex 1, FeIIPDP? (where PDP? = bis(3,5-dimethyl-4-methoxypyridyl-2-methyl)-(R,R)-2,2′-bipyrrolidine). The oxoiron(IV) species have been proposed to arise by O-O homolysis of the peroxyiron(III) or acylperoxyiron(III) intermediates formed during the presumed FeIII-FeV catalytic cycle and have generally been regarded as off-pathway. We generated complex 1IV=O (λmax = 730 nm, ? = 350 M-1 cm-1) directly from 1 and an oxygen atom donor IBXi-Pr (isopropyl 2-iodoxybenzoate) in acetonitrile in the temperature range from-35 to +25 °C under stopped-flow conditions. Species 1IV=O is metastable (half-life of 2.0 min at +25 °C), and its decay is accelerated in the presence of organic substrates such as thioanisole, alkenes, benzene, and cyclohexane. The reaction with cyclohexane-d12 is significantly slower (KIE = 4.9 ± 0.4), suggesting that a hydrogen atom transfer to 1IV=O is the rate limiting step. With benzene-d6, no significant isotope effect is observed (KIE = 1.0 ± 0.2), but UV-vis spectra show the concomitant formation of an intense 580 nm band likely due to the Fe(III)-phenolate chromophore, suggesting an electrophilic attack of 1IV=O on the aromatic system of benzene. Treatment of 1IV=O with H2O2 resulted in rapid decay of its 730 nm visible band (k = 102.6 ± 4.6 M-1 s-1 at-20 °C), most likely occurring by a hydrogen atom transfer from H2O2. In the presence of excess H2O2, the oxoiron(IV) is transformed into peroxyiron(III), as seen from the formation of a characteristic 550 nm visible band and geff = 2.22, 2.16, and 1.96 electron paramagnetic resonance (EPR) spectroscopy signals. Reductively formed 1III-OOH was able to re-enter the catalytic cycle of alkene epoxidation by H2O2, albeit with lower yields versus those of oxidatively formed (i.e., 1 + H2O2) peroxyiron(III) owing to a loss of ca. 40% active iron. As such, the oxoiron(IV) species can be reintroduced to the catalytic cycle with extra H2O2, acting as an iron reservoir. Alternatively, peroxycarboxylic acids, which have a stronger O-H bond dissociation energy, do not reduce 1IV=O, ensuring that more oxidant is productively employed in substrate oxidation. While this reaction with H2O2 may occur for other nonheme oxoiron(IV) complexes, the only previously reported examples are 3IV=O and 4IV=O, which are reduced by hydrogen peroxide 130- A nd 2900-fold more slowy, respectively (as in Angew. Chemie-Int. Ed. 2012, 51 (22), 5376-5380, DOI: 10.1002/anie.201200901).
Dioxo-molybdenum(VI) unsymmetrical Schiff base complex supported on CoFe2O4@SiO2 nanoparticles as a new magnetically recoverable nanocatalyst for selective epoxidation of alkenes
Ardakani, Mehdi Hatefi,Sabet, Mohammad,Samani, Mahnaz
, (2022/03/27)
In the present work, a dioxo-molybdenum unsymmetrical Schiff base complex, [MoO2(salenac-OH)], in which salenac-OH = [9-(2',4'-dihydroxyphenyl)-5,8-diaza-4-methylnona-2,4,8-trienato](-2), has been prepared and covalently immobilized on the sili
Polyamine-functionalized imidazolyl poly(ionic liquid)s for the efficient conversion of CO2 into cyclic carbonates
Cheng, Guoe,Ge, Yuansheng,Ke, Hanzhong,Li, Xiaoguang,Liu, Wei,Zhang, Qiang,Zou, Yizhen
, p. 273 - 281 (2022/01/19)
Global warming is becoming a challenging issue due to the emission of a large number of greenhouse gases, mainly CO2. The transformation of CO2 into chemicals with high additional value is considered a promising and sustainable way to solve the “greenhouse effect”. Herein, a series of polyamine-functionalized imidazolyl poly(ionic liquid)s (PILs) modified by triethylenetetramine (TETA) were synthesized as heterogeneous catalysts to convert CO2 into cyclic carbonates. The synergistic effect of nucleophile (bromide anions) and polyamine groups in promoting CO2 conversion was explored by density functional theory (DFT) calculations, which is critical to improve the catalytic performance. When the anions of ionic liquids acted as nucleophiles to attack the epoxide from the C–O bond with less steric hindrance, the substrate epoxide and CO2 can be activated by hydrogen bonding with amine group protons. Therefore, PILs modified by TETA (N4-PIL-x) have been verified to possess high efficiency and stable reusability for the cycloaddition of epoxides with CO2 without solvent, metal, and co-catalyst, of which N4-PIL-2 can achieve 98.0% conversion of epichlorohydrin (ECH) with a turnover frequency (TOF) value as high as 42.4 h?1 under ambient pressure; moreover, the complete conversion of epichlorohydrin is obtained in only 4 h at 1.0 MPa CO2 pressure.
Aldehyde-catalyzed epoxidation of unactivated alkenes with aqueous hydrogen peroxide
Kokotos, Christoforos G.,Kokotou, Maroula G.,Lotter, Dominik,Sparr, Christof,Triandafillidi, Ierasia
, p. 10191 - 10196 (2021/08/12)
The organocatalytic epoxidation of unactivated alkenes using aqueous hydrogen peroxide provides various indispensable products and intermediates in a sustainable manner. While formyl functionalities typically undergo irreversible oxidations when activating an oxidant, an atropisomeric two-axis aldehyde capable of catalytic turnover was identified for high-yielding epoxidations of cyclic and acyclic alkenes. The relative configuration of the stereogenic axes of the catalyst and the resulting proximity of the aldehyde and backbone residues resulted in high catalytic efficiencies. Mechanistic studies support a non-radical alkene oxidation by an aldehyde-derived dioxirane intermediate generated from hydrogen peroxide through the Payne and Criegee intermediates.
