- Windmill-type mixed-metal clusters containing Schiff-base ligands as an efficient catalyst for cyclohexene oxidation
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Two new mixed-metal clusters {CuM2(H2O)2[Cu(C14H16N2O3)Cl]6}·H2O (M = Mn 1, Zn 2) based on Schiff-base ligands were designed and synthesized by the reaction of 1,2-cyclohexanediamine-N,N′-bis-(3-carboxylsalicylide), copper chloride and zinc chloride or manganese chloride under solvothermal conditions. They were characterized by various techniques including single-crystal X-ray diffraction, powder X-ray diffraction (XPRD), elemental analysis, TG analysis, IR and UV-visible spectroscopy. Compounds 1 and 2 are isostructural, and display an interesting windmill-type structure built from a trinuclear mixed-metal center [CuM2(CO2)6(H2O)2] (M = Mn 1, Zn 2) linked with six [CuLCl] (L = C14H16N2O3) units. The oxidation of cyclohexene catalysed by 1 and 2 as heterogeneous catalysts was investigated and showed high activity. In addition, a magnetic study indicates that antiferromagnetic interactions exist in compound 1.
- Li, Xiaoqin,Ma, Dan,Cao, Bingran,Lu, Ying
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- Catalytic behavior of 1-(2-pyridylazo)-2-naphthol transition metal complexes encapsulated in y zeolite
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The goal of this study is the preparation of new heterogeneous catalysts to be used in the oxidation of organic molecules under mild conditions. The metals in zeolite (M-Y) were prepared by the ion exchange method. The in situ encapsulation of selected transition metal complexes as a guest, namely cobalt(II), nickel(II), copper(II), and zinc(II), with 1-(2-pyridylazo)-2- naphthol (PAN) ligand in supercages of Y zeolite (host) was accomplished by the flexible ligand method. The coordination geometry of neat and Y-encapsulated metal complexes has been determined by molecular simulations. The resulting catalysts were fully characterized by different techniques (FTIR, SEM, and chemical analysis), and the results indicated that complexes were encapsulated in supercages of Y zeolite. Catalytic studies were performed in liquid phase for cyclohexene and cyclohexanol oxidations, by using tert-butylhydroperoxide as the oxidizing agent at 40 and 60 °C, respectively. All prepared catalysts exhibited catalytic activity for the oxidation reactions.
- Kuzniarska-Biernacka,Biernacki,Magalhaes,Fonseca,Neves
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- Lanthanide metal-organic frameworks for catalytic oxidation of olefins
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Two isostructural lanthanide metal-organic frameworks (Ln-MOF-589, Ln = La3+, Ce3+), constructed from a tetratopic linker, benzoimidephenanthroline tetracarboxylic acid (H4BIPA-TC), have been solvothermally synthesized and characterized. These Ln-MOF-589 materials consist of Lewis acid [Ln2(-COO)6(-COOH)2(H2O)6] units and a naphthalene diimide core, which exhibited promising catalytic activity for the oxidation of olefins. Among them, Ce-MOF-589 exhibited outstanding performance with high conversions of styrene and cyclohexene (94 and 90%, respectively), and good selectivities towards styrene oxide and 2-cyclohexen-1-one (85, and 95%, respectively). Notably, the catalytic activity of Ce-MOF-589 outperformed that of homogeneous and heterogeneous catalysts, and representative MOFs. Also, Ce-MOF-589 can be recycled for at least up to six cycles with no significant loss of catalytic performance.
- Tran,Nguyen, Phuong T. K.
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p. 2090 - 2102
(2021/02/06)
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- Allylic oxidation of olefins with a manganese-based metal-organic framework
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Selective oxidation of olefins to α,β-unsaturated ketones under mild reaction conditions has attracted considerable interest, since α,β-unsaturated ketones can serve as synthetic precursors for various downstream chemical products. The major inherent challenges with this chemical oxidation are chemo- and regio-selectivity as well as environmental concerns, i.e. catalyst recycle, safety and cost. Using atmospheric oxygen as an environmentally friendly oxidant, we found that a metal-organic framework (MOF) constructed with Mn and a tetrazolate ligand (CPF-5) showed good activity and selectivity for the allylic oxidation of olefins to α,β-unsaturated ketones. Under the optimized conditions, we could achieve 98% conversion of cyclohexene and 87% selectivity toward cyclohexanone. The combination of a substoichiometric amount of TBHP (tert-butylhydroperoxide) and oxygen not only provides a cost effective oxidation system but significantly enhances the selectivity to α,β-unsaturated ketones, outperforming most reported oxidation methods. This catalytic system is heterogeneous in nature, and CPF-5 could be reused at least five times without a significant decrease in its catalytic activity and selectivity.
- Chen, Jingwen,Chen, Minda,Zhang, Biying,Nie, Renfeng,Huang, Ao,Goh, Tian Wei,Volkov, Alexander,Zhang, Zhiguo,Ren, Qilong,Huang, Wenyu
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supporting information
p. 3629 - 3636
(2019/07/10)
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- A highly efficient heterogeneous catalyst of cobalt-based coordination polymers for aerobic epoxidation of cyclohexene
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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.
- Yu, Fan
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p. 5074 - 5078
(2018/09/09)
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- Copper-Functionalized Metal–Organic Framework as Catalyst for Oxidant-Controlled Partial Oxidation of Cyclohexene
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Microwave irradiation is exploited for the facile, one-step functionalization of Cu(acac)2 to –NH2 pendant groups of MIL-53(Al)-NH2, a metal–organic framework material, under mild reaction conditions and a short reaction time. PXRD, XPS, XAS, and EPR spectroscopy are used to investigate the structure and chemical nature of the copper species on the framework. The copper center exists in the +2 oxidation state with a square-planar geometry and NO3 coordination environment. The copper complex is anchored to the framework by imine bond formation. This copper-functionalized MIL-53(Al)-NH2 or MIL-53[Cu] is employed in the catalytic oxidation of olefins using molecular oxygen (O2) or tert-butyl hydroperoxide (TBHP) as the oxidant. The chemoselectivities of the oxidation products depend on the type of oxidant and substrate. When O2 is used as the oxidant and isobutyraldehyde as the co-oxidant in the oxidation of cyclohexene with MIL-53[Cu], cyclohexene oxide is the major product. However, when TBHP is employed as the oxidant, 2-cyclohexen-1-one is the major product. Furthermore, the catalyst can be reused at least three times without a significant loss in activity.
- Chotmongkolsap, Pannapat,Bunchuay, Thanthapatra,Klysubun, Wantana,Tantirungrotechai, Jonggol
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p. 703 - 712
(2018/02/09)
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- Cobalt(II) complexes with N,N,N-scorpionates and bidentate ligands: Comparison of hydrotris(3,5-dimethylpyrazol-1-yl)borate Tp? vs. Phenyltris(4,4-dimethyloxazolin-2-yl)borate ToM to control the structural properties and reactivities of cobalt centers
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Scorpionate ligands Tp? (hydrotris(3,5-dimethylpyrazol-1-yl)borate) and ToM (tris(4,4- dimethyloxazolin-2-yl)phenylborate) complexes of cobalt(II) with bidentate ligands were synthesized. Both Tp? and ToM coordinate to cobalt(II) in a tridentate fashion when the bidentate ligand is the less hindered acetylacetonate. In crystal structures, the geometry of cobalt(II) supported by the N3O2 donor set in the Tp? complex is a square-pyramid, whereas that in the ToM complex is close to a trigonal-bipyramid. Both Tp?- and ToM-acac complexes exhibit solvatochromic behavior, although the changing structural equilibria of these complexes in MeCN are quite different. In the bis(1-methylimidazol-2-yl)methylphenylborate (LPh) complexes, Tp? retains the tridentate (k3) mode, whereas ToM functions as the bidentate (k2) ligand, giving the tetrahedral cobalt(II) complex. The bowl-shaped cavity derived from the six methyl groups on ToM lead to susceptibility to the bulkiness of the opposite bidentate ligand. The entitled scorpionate compounds mediate hydrocarbon oxidation with organic peroxides. Allylic oxidation of cyclohexene occurs mainly on the reaction with tert-butyl hydroperoxide (TBHP), although the catalytic efficiency of the scorpionate ligand complexes is lower than that of Co(OAc)2 and Co(acac)2. On cyclohexane oxidation with meta-chloroperbenzoic acid (mCPBA), both ToM and Tp? complexes function as catalysts for hydroxylation. The higher electron-donating ToM complexes show faster initial reaction rates compared to the corresponding Tp? complexes.
- Nishiura, Toshiki,Uramoto, Takahiro,Takiyama, Yuichiro,Nakazawa, Jun,Hikichi, Shiro
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- 2D Co-based coordination polymer with a histidine derivative as an efficient heterogeneous catalyst for the oxidation of cyclohexene
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The hydrothermal reaction of CoCl2 and 4-((1-carboxy-2-(1H-imidazol-4-yl)ethylamino)methyl)benzoic acid (H2L) generated a {Co2(H2O)}-based 2D coordination framework, {(Co(L)(H2O))2(H2O)}n (1). Heterogeneous catalytic experiments on the allylic oxidation of cyclohexene show that activated 1 exhibits high catalytic activity using tert-butylhydroperoxide (t-BuOOH) as the oxidant toward the formation of tert-butyl-2-cyclohexenyl-1-peroxide. The activation energy for the oxidation of cyclohexene with catalyst 1 was approximately calculated as 91.98 kJ mol-1. This work demonstrates that a degree of creativity in the coordinatively unsaturated metal sites in CPs could significantly enhance their heterogeneous catalytic activity and selectivity.
- Yu, Fan,Xiong, Xin,Huang, Kexing,Zhou, Yinliu,Li, Bao
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p. 2126 - 2132
(2017/04/14)
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- Microwave-assisted one-pot functionalization of metal-organic framework MIL-53(Al)-NH2 with copper(ii) complexes and its application in olefin oxidation
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A simple, rapid, and efficient functionalization of the metal-organic framework MIL-53(Al)-NH2 with copper(ii) complexes by microwave irradiation is described. The one-pot post-synthetic modification was based on the Schiff base reaction between the aldehyde added and the primary aryl amino group in the organic linker of MIL-53(Al)-NH2, which afforded coordination sites for copper(ii). The effects of synthetic parameters such as solvent, reaction time, and reactant ratio were evaluated. The functionalized materials were structurally characterized and examined for potential applications in catalysis. The copper complex functionalized MIL-53(Al) was active towards the oxidation of olefins with tert-butyl hydroperoxide as an oxidant. The results showed that if the olefin possessed allylic hydrogens such as cyclohexene, allylic oxidation products were obtained, but epoxide was the major product obtained from terminal olefins without allylic hydrogens. The reaction mechanism based on density functional theory calculations provides some insights into the observed experimental results.
- Bunchuay,Ketkaew,Chotmongkolsap,Chutimasakul,Kanarat,Tantirungrotechai,Tantirungrotechai
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p. 6069 - 6079
(2017/12/26)
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- Synthesis, structure, catalytic and magnetic properties of a pyrazole based five coordinated di-nuclear cobalt(II) complex
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The reaction of 4-methyl-2,6-bis(3,5-dimethyl-1H-pyrazol-1-yl)methyl)phenol and Co(NO3)2·6H2O in MeCN gives rise to [Co2(L)2(N3)2] (1), a dinuclear five coordinated complex of Co(II), in satisfactory yield. The complex has been characterized by C, H and N microanalyses, FT-IR and UV-Vis spectral measurements. A single crystal X-ray diffraction study of 1 reveals that each Co(II) atom is in a distorted square-pyramidal geometry. Electrochemical studies in CH3CN showed that the Co(II)-Co(III)/Co(III)-Co(III) redox couple appears to be quasi-reversible (E1/2 = 0.409 V), while the corresponding Co(II)-Co(III)/Co(II)-Co(II) couple is mostly irreversible (E1/2 = -0.447 V). This complex displays modest catalytic activity toward the oxidation of various allylic compounds using TBHP as an oxidant in MeCN under mild conditions. A radical trapped experiment carried out in the presence of 4-tert-butylphenol clearly reveals that the epoxidation reactions occur purely through a radical pathway rather than a concerted one. Low temperature magnetic studies showed that the present Co(II) dimeric complex possesses a high positive magnetic anisotropy (D = +29.8 cm-1) and a weak ferromagnetic exchange interaction (2J = +10.3 cm-1).
- Alam, Rabiul,Pal, Kaberi,Shaw, Bikash Kumar,Dolai, Malay,Pal, Nabanita,Saha, Shyamal Kumar,Ali, Mahammad
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- PdCl2 immobilized on metal-organic framework CuBTC with the aid of ionic liquids: Enhanced catalytic performance in selective oxidation of cyclohexene
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Metal-organic framework CuBTC was employed as a support to immobilize PdCl2 with the aid of ionic liquids (ILs). The as-synthesized PdCl2-ILs/CuBTC catalyst was studied in selective oxidation of cyclohexene with molecular oxygen as an oxidant and TBHP as an initiator. It is found that the allylic oxidation and radical oxidation processes are main reaction pathways. More importantly, the enhancement of catalytic activity in the oxidation of cyclohexene is observed over the PdCl2-IL/CuBTC catalyst due to Pd-Cu cooperative catalysis. Furthermore, ionic liquids could have a very favourable role in the stabilization of Pd(ii) species and improvement of catalyst reusability.
- Luo, Qun-Xing,Ji, Min,Park, Sang-Eon,Hao, Ce,Li, Yan-Qin
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p. 33048 - 33054
(2016/05/09)
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- Bis(carboxyphenyl)-1,2,4-triazole Based Metal-Organic Frameworks: Impact of Metal Ion Substitution on Adsorption Performance
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This work presents the syntheses and comprehensive characterization of six paddlewheel based metal-organic frameworks (MOFs) with the general formula ∞ 3[M2L2] (M = Cu, Co, Zn; L = bis(carboxyphenyl)-1,2,4-triazole) forming an isoreticular series with rutile (rtl) topology. These microporous materials are suitable for a systematic investigation of structure-property relationships based on the impact of the metal ion. Depending on the metal ion, the calculated porosities and the pore diameters reach from 58% to 61% and 300 to 750 pm, respectively. Simultaneous thermal analysis and temperature dependent PXRD studies reveal varying thermal behavior with stabilities up to 400 °C. In the case of syntheses with various Co2+/Cu2+, Co2+/Zn2+, and Cu2+/Zn2+ ratios, ICP-OES analyses and SEM-EDX studies confirm the formation of mixed metal MOFs and the metal ion distribution in the bulk samples as well as within the crystals. For the systematic investigation of CO2 (298 K) and N2 (77 K) adsorption properties, all materials were previously subjected to extraction with supercritical CO2. Depending on the metal ion, this procedure causes different phase transitions for each compound. As a result, adsorption studies reveal varying network flexibility for these MOFs. This study is one of the rare examples demonstrating that targeted modification of gate opening pressure, hysteresis shape, and adsorbed amounts of CO2 or N2 are possible by choice of the metal ion. This finding is supported by adsorption studies on the mixed metal MOF ∞3[(Cu0.48Co0.52)2(p-L)2)], showing CO2 adsorption/desorption characteristics of both homonuclear copper and cobalt materials, whereas N2 does not induce gate opening of the framework, as observed for the cobalt MOF. Furthermore, catalytic studies reveal that ∞ 3[Cu2(p-L)2)] is a suitable catalyst for the oxidation of cyclohexene with tert-butylhydroperoxide (TBHP) with high conversion of the starting materials and good selectivity. Its robustness under the applied catalysis conditions leads to similar conversions in repetition measurements.
- Kobalz,Kobalz,M?llmer,Junghans,Lange,Bergmann,Dietrich,Wecks,Gl?ser,Krautscheid
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supporting information
p. 6938 - 6948
(2016/07/26)
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- Tuning of the reaction parameters to optimize allylic oxidation of cyclohexene catalyzed by zeolite-Y entrapped transition metal complexes
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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.
- Godhani, Dinesh R.,Nakum, Haresh D.,Parmar, Digvijaysinh K.,Mehta, Jignasu P.,Desai, Nisheeth C.
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- Enhanced Catalysis Activity in a Coordinatively Unsaturated Cobalt-MOF Generated via Single-Crystal-to-Single-Crystal Dehydration
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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).
- Ren, Hai-Yun,Yao, Ru-Xin,Zhang, Xian-Ming
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p. 6312 - 6318
(2015/07/15)
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- Chiral Co(II) metal-organic framework in the heterogeneous catalytic oxidation of alkenes under aerobic and anaerobic conditions
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The chiral Co(II) MOF [Co(l-RR)(H2O)·H2O] ∞ [1; l-RR = (R,R)-thiazolidine-2,4-dicarboxylate] has been exploited in the catalytic oxidation of different alkenes (cyclohexene, (Z)-cyclooctene, 1-octene) using either tert-butyl hydroperoxide ( tBuOOH) or molecular oxygen (O2) as oxidants. Different chemoselectivities are observed, both substrate- and oxidant-dependent. A moderate enantioselectivity is also obtained in the case of prochiral precursors, revealing the chiral induction ability of the optically pure metal environment. The interaction of O2 with the exposed metal sites in 1 (after material preactivation and consequent removal of the coordinated aquo ligand) has been studied through TPD-MS analysis combined with DFT calculations, with the aim of probing effective oxygen uptake by the heterogeneous catalyst and unraveling the nature of the active species in the catalytic oxidation process under aerobic conditions. Theoretical results indicate the presence of an η1-superoxo species at the cobalt center, with concomitant Co(II) ? Co(III) oxidation. Finally, the experimental estimation of the O2 adsorption enthalpy is found to be in good agreement with the calculated binding energy.
- Tuci, Giulia,Giambastiani, Giuliano,Kwon, Stephanie,Stair, Peter C.,Snurr, Randall Q.,Rossin, Andrea
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p. 1032 - 1039
(2014/04/03)
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- Mn(ii) acetate: An efficient and versatile oxidation catalyst for alcohols
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A homogeneous catalytic system consisting of Mn(ii) acetate (18 μmol), tert-butylhydroperoxide (2.5 mmol), acetonitrile (1.5 mL) and trifluoroacetic acid (91 μmol) was developed for efficient and selective oxidation of various alcohols (1 mmol). The system yielded good to quantitative conversions (42-100%) of various secondary alcohols, such as 2-octanol, fenchyl alcohol and borneol, to their corresponding ketones. Primary alcohols, for example 1-octanol and differently substituted benzyl alcohols, were mainly converted to their corresponding carboxylic acids. Studies with a selection of hydrocarbons, tertiary amines and a cyclic ether isochroman showed that besides alcohols, other substrates can be oxidised as well.
- Raeisaenen, Minna T.,Al-Hunaiti, Afnan,Atosuo, Elisa,Kemell, Marianna,Leskelae, Markku,Repo, Timo
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p. 2564 - 2573
(2014/07/22)
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- Catalytic performance of vanadium MIL-47 and linker-substituted variants in the oxidation of cyclohexene: A combined theoretical and experimental approach
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The epoxidation of cyclohexene has been investigated on a metal-organic framework MIL-47 containing saturated V+IV sites linked with functionalized terephthalate linkers (MIL-47-X, X=OH, F, Cl, Br, CH3, NH2). Experimental catalytic tests have been performed on the MIL-47-X materials to elucidate the effect of linker substitution on the conversion. Notwithstanding the fact that these substituted materials are prone to leaching in the performed catalytic tests, the initial catalytic activity of these materials correlates with the Hammett substituent constants. In general, substituents led to an increased activity relative to the parent MIL-47. To rationalize the experimental findings, first-principles kinetic calculations were performed on periodic models of MIL-47 to determine the most important active sites by creating defect structures in the interior of the crystalline material. In a next step these defect structures were used to propose extended cluster models, which are able to reproduce in an adequate way the direct environment of the active metal site. An alkylperoxo species V +VO(OOtBu) was identified as the most abundant and therefore the most active epoxidation site. The structure of the most active site was a starting basis for the construction of extended cluster models including substituents. They were used for quantifying the effect of functionalization of the linkers on the catalytic performance of the heterogeneous catalyst MIL-47-X. Electron-withdrawing as well as electron-donating groups have been considered. The epoxidation activity of the functionalized models has been compared with the measured experimental conversion of cyclohexene. The agreement is fairly good. This combined experimental-theoretical study makes it possible to elucidate the structure of the most active site and to quantify the electronic modulating effects of linker substituents on the catalytic activity. Copyright
- Vandichel, Matthias,Biswas, Shyam,Leus, Karen,Paier, Joachim,Sauer, Joachim,Verstraelen, Toon,Van Der Voort, Pascal,Waroquier, Michel,Van Speybroeck, Veronique
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p. 1183 - 1197
(2014/11/27)
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- N-heterocyclic carbene dirhodium(II) complexes as catalysts for allylic and benzylic oxidations
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The experimental conditions (solvent, base, temperature and oxidant) for allylic and benzylic oxidation reactions catalyzed by dirhodium(II)/N- heterocyclic carbene (NHC) complexes were optimized for the first time in this work. The oxidations of cyclohexene and fluorene were used as model reactions. Two optimized experimental conditions for both types of oxidations were found, which resulted in their ketone [aerobic conditions, 40 °C, 1 equiv. tBuOOH (TBHP)] or tert-butyl peroxide derivatives (anaerobic conditions, 25 °C, 2 equiv. TBHP). The dirhodium(II) complexes undergo a single-electron reversible oxidation by cyclic voltammetry in CH2Cl2, which is assigned to the Rh24+/Rh25+ redox couple at an oxidation potential that is lowered upon sequential axial coordination of further ligands to the Rh-Rh centre. The oxidation potential is discussed in terms of the electron-donor character of the NHC ligand, which was shown to act as an effective electron-releaser to the Rh2 4+ centre, and the electrochemical behaviour is compared to the observed catalytic activity. An N-heterocyclic carbene (NHC) ligand at the axial position of Rh2(carboxylate)4 complexes triggers considerable changes in the electrochemical behaviour of the formed complexes, which also catalyze allylic and benzylic oxidations. Copyright
- Coelho, Jaime A. S.,Trindade, Alexandre F.,Wanke, Riccardo,Rocha, Bruno G. M.,Veiros, Luis F.,Gois, Pedro M. P.,Pombeiro, Armando J. L.,Afonso, Carlos A. M.
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supporting information
p. 1471 - 1478
(2013/05/09)
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- Electrochemical and catalytic studies of a manganese(III)complex with a tetradentate schiff-base ligand encapsulated in NaY zeolite
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The manganese(III) complex with a Schiff-base salen-type ligand (1,5-bis{[(1E)-(2-hydroxyphenyl)methylene]amino}-1H-imidazole-4-carbonitrile) has been encapsulated in the nanopores of a Y zeolite by using two different methodologies, the flexible ligand and in situ complex preparation methods. Cyclic voltammetry studies revealed that the neat complex undergoes reversible oxidation in dmf, which has been attributed to the MnII/III redox couple, whereas the two heterogeneous catalysts show different electrochemical behaviour in aqueous medium. The encapsulated and non-encapsulated homogeneous MnIIIsalen complexes were screened as catalysts for olefin oxidation by using tBuOOH as the oxygen source in different solvents. Under the optimized conditions, the catalysts exhibited moderate activity. Both heterogeneous catalysts catalysed the oxidation of cyclohexene with tBuOOH, primarily to give the allylic oxidation products. These catalysts were found to be reusable after the catalytic cycle, but with some loss of activity. A DFT study confirmed the distortion of the complex in the zeolite cage, the main difference being observed for the bonded chloride. Copyright
- Kuzniarska-Biernacka, Iwona,Rodrigues, Otilia,Carvalho, Maria Alice,Parpot, Pier,Biernacki, Krzysztof,Magalhaes, Alexandre Lopes,Fonseca, Antonio Mauricio,Neves, Isabel Correia
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p. 2768 - 2776
(2013/07/11)
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- The coordinatively saturated vanadium MIL-47 as a low leaching heterogeneous catalyst in the oxidation of cyclohexene
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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.
- 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
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experimental part
p. 196 - 207
(2012/03/08)
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- Novel reactivity of N-bridged diiron phthalocyanine in the activation of C-H bonds: Hydroacylation of olefins as an example of the efficient formation of C-C bonds
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Bridge over troubled iron: An N-bridged diiron tetra-tert- butylphthalocyanine complex, usually employed for oxidation reactions, also catalyzes the addition of acetaldehyde to olefins (see scheme) to provide methylketones with a high selectivity (up to 92%) and high turnover numbers (3600-5700). Copyright
- Alvarez, Leonardo X.,Kudrik, Evgeny V.,Sorokin, Alexander B.
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supporting information; experimental part
p. 9298 - 9301
(2011/10/09)
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- Pyrazolate-based cobalt(II)-containing metal-organic frameworks in heterogeneous catalytic oxidation reactions: Elucidating the role of entatic states for biomimetic oxidation processes
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Crystal structures of two metal-organic frameworks (MFU-1 and MFU-2) are presented, both of which contain redox-active CoII centres coordinated by linear 1,4-bis[(3,5-dimethyl)pyrazol-4-yl] ligands. In contrast to many MOFs reported previously, these compounds show excellent stability against hydrolytic decomposition. Catalytic turnover is achieved in oxidation reactions by employing tert-butyl hydroperoxide and the solid catalysts are easily recovered from the reaction mixture. Whereas heterogeneous catalysis is unambiguously demonstrated for MFU-1, MFU-2 shows catalytic activity due to slow metal leaching, emphasising the need for a deeper understanding of structure-reactivity relationships in the future design of redox-active metal-organic frameworks. Mechanistic details for oxidation reactions employing tert-butyl hydroperoxide are studied by UV/Vis and IR spectroscopy and XRPD measurements. The catalytic process accompanying changes of redox states and structural changes were investigated by means of cobalt K-edge X-ray absorption spectroscopy. To probe the putative binding modes of molecular oxygen, the isosteric heats of adsorption of O2 were determined and compared with models from DFT calculations. The stabilities of the frameworks in an oxygen atmosphere as a reactive gas were examined by temperature-programmed oxidation (TPO). Solution impregnation of MFU-1 with a co-catalyst (N-hydroxyphthalimide) led to NHPI@MFU-1, which oxidised a range of organic substrates under ambient conditions by employing molecular oxygen from air. The catalytic reaction involved a biomimetic reaction cascade based on free radicals. The concept of an entatic state of the cobalt centres is proposed and its relevance for sustained catalytic activity is briefly discussed.
- Tonigold, Markus,Lu, Ying,Mavrandonakis, Andreas,Puls, Angela,Staudt, Reiner,Moellmer, Jens,Sauer, Joachim,Volkmer, Dirk
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experimental part
p. 8671 - 8695
(2011/10/04)
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- Catalytic performance of ceria nanorods in liquid-phase oxidations of hydrocarbons with tert-butyl hydroperoxide
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The CeO2 nanorods (CeNR) promote the oxidation of ethylbenzene (PhEt) and cyclohexene with t-BuOOH, at temperatures as low as 55 °C. For both substrates the saturated C-H bonds are preferentially activated over the unsaturated ones. The catalyst seems fairly stable towards leaching phenomena. The liquid-phase oxidation catalysis may be associated with the Ce 3+/Ce4+ inter-conversion in the one-electron redox processes mediating the formation of tert-butyl-(per)oxy radicals. CeNR is very effective in H2O2 disproportionation. Pre-treatment of CeNR with H2O2 or t-BuOOH prior to the catalytic reaction enhances the reaction rate of PhEt with t-BuOOH in comparison to CeNR. Textural characterization and spectroscopic studies suggest that catalytic activation is associated to defect sites.
- Macedo, Andreia G.,Fernandes, Silvia E. M.,Valente, Anabela A.,Ferreira, Rute. A. S.,Carlos, Luis D.,Rocha, Joao
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experimental part
p. 747 - 765
(2010/04/29)
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- The remarkable catalytic activity of the saturated metal organic framework V-MIL-47 in the cyclohexene oxidation
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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.
- Leus, Karen,Muylaert, Ilke,Vandichel, Matthias,Marin, Guy B.,Waroquier, Michel,Van Speybroeck, Veronique,Van Der Voort, Pascal
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body text
p. 5085 - 5087
(2010/10/04)
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- Selective epoxidation of cyclohexene by a square-planar Ru complex immobilized into mesoporous silicate FSM-16
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The Ru complex, [RuII(babp)(dmso)2] (1) (H 2babp = 6,6′-bis(benzoylamino)-2,2′-bipyridine), was immobilized into mesoporous silicate FSM-16. The heterogeneous catalyst demonstrated a more selective epoxidation compared with the homogeneous 1. Copyright
- Okumura, Takeshi,Takagi, Hideki,Funahashi, Yasuhiro,Ozawa, Tomohiro,Fukushima, Yoshiaki,Jitsukawa, Koichro,Masuda, Hideki
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p. 122 - 123
(2007/10/03)
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- Diverse pathways for the palladium(II)-mediated oxidation of olefins by tert-butylhydroperoxide
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(Matrix presented) New procedures are described for the palladium-catalyzed oxidation of olefins by tert-butylhydroperoxide under slightly basic conditions in CH2Cl2 solution at 0-25°C.
- Yu, Jin-Quan,Corey
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p. 2727 - 2730
(2007/10/03)
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- Temperature effect on the epoxidation of olefins by an iron(III) porphyrin complex and tert-alkyl hydroperoxides
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An electron-deficient iron porphyrin complex catalyzes the epoxidation of olefins by tert-alkyl hydroperoxides via radical-free oxidation reactions in aprotic solvent; the epoxidation reactions were markedly influenced by reaction temperature and high yields of epoxide products were obtained with retention of stereospecificity at low temperature.
- Nam,Oh,Mi Hee Lim,Choi,Han,Jhon
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p. 1787 - 1788
(2007/10/03)
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- Ingold-Fischer "Persistent Radical Effect", Solvent Effect, and Metal Salt Oxidation of Carbon-Centered Radicals in the Synthesis of Mixed Peroxides from tert-Butyl Hydroperoxide
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Mixed peroxides are formed from tert-butyl hydroperoxide (TBH), tert-butyl peroxalate (TBP), and a variety of substrates (p-cresol, cyclohexene, styrene, α-methylstyrene, acrylonitrile, 2-methylcyclohexanone). Also, the oxidation of THF in the presence of acrylonitrile under the same conditions gives the mixed peroxide, generated by addition of the tetrahydrofuranyl radical to the double bond and the cross-coupling of the radical adduct with the tert-butylperoxyl radical. Similarly, benzoyl peroxide, TBH, and acrylonitrile give the mixed peroxide by oxidative arylation of the double bond. Paradoxically, TBH acts as effective inhibitor of the polymerization of vinyl monomers (acrylonitrile, styrene). An overall kinetic evaluation suggests that the conditions for the Ingold-Fischer "persistent radical effect", characterized by the simultaneous formation of a persistent and a transient radical, are fulfilled in all cases. The reactions are strongly affected by solvents, which form hydrogen bonds with TBH. Catalytic amounts of Cu(II) and Fe(III) salts influence the selectivity; the possibility that the mixed peroxides can also be generated by metal salt oxidation of carbon-centered radicals is discussed.
- Bravo, Anna,Bjorsvik, Hans-Rene,Fontana, Francesca,Liguori, Lucia,Minisci, Francesco
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p. 3849 - 3857
(2007/10/03)
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- Die Titan(IV)-katalysierte Epoxidierung von Alkenen durch tert-Alkylhydroperoxide
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Keywords: Epoxidierungen; Alkylhydroperoxide; Heterogene Katalyse; Titansilicalite
- Oldroyd, Richard D.,Thomas, John Meurig,Maschmeyer, Thomas,MacFaul, Philip A.,Snelgrove, Darren W.,et al.
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p. 2966 - 2969
(2007/10/03)
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- Oxidation of cyclohexene with t-butyl hydroperoxide catalyzed by transition metal oxide clusters
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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.
- Zhang, Cuiju,Ozawa, Yoshiki,Hayashi, Yoshihito,Isobe, Kiyoshi
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p. C21 - C26
(2007/10/02)
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- Cobalt(III) Alkylperoxy Complexes. Synthesis, X-ray Structure, and Role in the Catalytic Decomposition of Alkyl Hydroperoxides and in the Hydroxylation of Hydrocarbons.
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Novel cobalt(III) alkylperoxy complexes with the general formula Co(R''BPI)(OCOR')(OOR) and Co(BPB)(OOt-Bu)(4-Mepy) were synthesized from the reaction of alkyl hydroperoxides with their Co(II) precusor, and characterized by physicochemical methods.The X-ray structure of Ib (R'' = H, R' = Ph, R = t-Bu) revealed a distorted octahedral environment with a chelating carboxylate moiety and an apically bonded tert-butylperoxy group.The reactivity of cobalt(III) alkylperoxy complexes toward hydrocarbons was found to be dependent on their thermal decomposition rate, with type I complexes being the most reactive ones.Saturated hydrocarbons are oxidized by Co(III) tert-butylperoxy complexes into alcohols, ketones, and tert-butylperoxy products.The hydroxylation reaction preferentally occurs at the more nucleophilic C-H bonds with extensive epimerization at the hydroxylated carbon atom.Hydrocarbons having labile allylic or benzylic C-H bonds react beginning at room temperature to give a large amount of allylic or benzylic tert-butyl peroxide.Olefins having no allylic hydrogen atom are preferentially transformed into epoxides.The catalytic hydroxylation of alkanes by t-BuOOH in the presence of complexes I-III has the same characteristics as the stoichiometric reaction.The homolytic decomposition and reactivity of cobalt(III) alkylperoxy complexes is discussed in the context of the Haber-Weiss mechanism of alkyl hydroperoxide decomposition and of hydrocarbon hydroxylation by first-row transition-metal peroxides.
- Saussine, Lucien,Brazi, Eric,Robine, Alain,Mimoun, Hubert,Fischer, Jean,Weiss, Raymond
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p. 3534 - 3540
(2007/10/02)
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- Selenium Dioxide Oxidation of Endocyclic Olefins. Evidence for a Dissociation-Recombination Pathway
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The selenium-catalyzed oxidation of some simple alicyclic olefins with tert-butyl hydroperoxide produced, in addition to the expected allylic alcohols, allylic tert-butyl peroxides and allylic tert-butyl ethers.Unlike the peroxides, the ether products were not inhibited by hydroquinone, and their relative amounts increased with decreasing ring size.Analogous products were detected in minor amounts in the selenium dioxide-tert-butyl hydroperoxide oxidation of β-pinene, with isomer distribution suggestive of a symmetrical intermediate.It is proposed that the etherproducts arise via a dissociation-recombination pathway competitive with the sigmatropic shift leading to the alcohol.Examination of the literature suggests that such a pathway may also be significant in selenium dioxide oxidations of small ring compounds in which ring oxidation occurs and may lead to unexpected products in which the double bond has moved from its original position.
- Warpehoski, M. A.,Chabaud, B.,Sharpless, K. B.
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p. 2897 - 2900
(2007/10/02)
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