- Copper based coordination polymers based on metalloligands: Utilization as heterogeneous oxidation catalysts
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This work presents the synthesis and characterization of two Cu(ii)-based coordination polymers prepared by utilizing two different Co(iii)-based metalloligands offering appended arylcarboxylic acid groups. Both coordination polymers are three-dimensional in nature and present pores and channels filled with water molecules. Both coordination polymers function as heterogeneous catalysts for the epoxidation of various olefins using O2 while employing isobutyraldehyde as the coreductor and for peroxide-mediated oxidation of assorted benzyl alcohols. The catalytic results illustrate efficient oxidation reactions, whereas the hot-fltration test and leaching experiments indicate the true heterogeneous nature of the catalysis.
- Kumar, Gulshan,Hussain, Firasat,Gupta, Rajeev
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p. 16985 - 16994
(2019/01/03)
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- Selective oxidation of styrene catalyzed by cerium-doped cobalt ferrite nanocrystals with greatly enhanced catalytic performance
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The rare earth metal Ce-doped cobalt ferrite samples CexCo1?xFe2O4 (x?=?0.1, 0.3, 0.5) were prepared by the sol–gel autocombustion route. The as-prepared samples were characterized by X-ray diffractometry, scanning electron microscopy, transmission electron microscopy, ICP–atomic emission spectroscopy, and N2 physisorption. Their catalytic performance was evaluated in oxidation of styrene using hydrogen peroxide (30%) as oxidant. Compared with pristine CoFe2O4, the Ce-doped samples were found to be more efficient catalysts for the oxidation of styrene to benzaldehyde, with greatly enhanced catalytic performance. Especially, when Ce0.3Co0.7Fe2O4 was used as catalyst, 90.3% styrene conversion and 91.5% selectivity for benzaldehyde were obtained at 90?°C for 9?h reaction. The catalyst can be magnetically separated easily for reuse, and no obvious loss of activity was observed when it was reused in five consecutive runs.
- Tong, Jinhui,Li, Wenyan,Bo, Lili,Wang, Huan,Hu, Yusen,Zhang, Zhixia,Mahboob, Abdulla
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p. 474 - 481
(2016/11/18)
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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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- Manganese- and cobalt-based coordination networks as promising heterogeneous catalysts for olefin epoxidation reactions
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We demonstrate the synthesis of Mn2+- and Co2+-based coordination networks using two Co3+-based metalloligands differing by the position of the appended arylcarboxylate groups. The structural analyses reveal topologically distinct networks with pores of variable dimensions allowing facile diffusion of substrates and/or reagents. All four networks function as heterogeneous catalysts for the olefin epoxidation reactions using tert-butyl-hydroperoxide without any requirement of solvent or additive. Control and optimization experiments illustrate recyclable network-based catalysts that make them attractive candidates for the "greener" oxidation chemistry processes.
- Kumar, Girijesh,Kumar, Gulshan,Gupta, Rajeev
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p. 2603 - 2615
(2015/03/30)
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- Mononuclear complexes of amide-based ligands containing appended functional groups: Role of secondary coordination spheres on catalysis
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Amide-based ligands H2L1, H2L2 and H2L3 containing thiazole, thiazoline and benzothiazole appended groups have been used to synthesize Zn2+ (1 and 3), Cd2+ complexes (2 and 4), and a Mn2+ complex (5). In all cases, potentially multidentate ligands create a meridional N3 coordination environment around the M(ii) ion whereas additional sites are occupied by labile nitrate ions in 1-4 and MeOH in 5. Interestingly, metal complexation caused the migration of protons from amidic N-H sites to the appended heterocyclic rings in complexes 1-4. Structural studies show that the protonated heterocyclic rings in these complexes create a hydrogen bond based cavity adjacent to the metal ion. Importantly, binding studies confirm that the substrates are bound within the complex cavity closer to the Lewis acidic metal in all complexes including the oxidation-sensitive Mn ion in complex 5. All complexes have been utilized as the reusable and heterogeneous catalysts for ring-opening reactions of assorted epoxides, cyanation reactions of various aldehydes, and epoxidation reactions of several olefins. This journal is
- Bansal, Deepak,Kumar, Gulshan,Hundal, Geeta,Gupta, Rajeev
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p. 14865 - 14875
(2015/02/19)
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- Olefin epoxidation with tert-BuOOH catalyzed by vanadium polyoxometalate immobilized on ionic liquid-modified MCM-41
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Preparation and characterization of vanadium-containing polyphosphomolybdates supported on ionic liquid-modified MCM-41, MCM-41-Im, are reported. The catalyst, [PVMo@MCM- 41-Im], was characterized by elemental analysis, X-ray diffraction, scanning electron microscopy and also FT-IR, and UV-Vis spectroscopic methods. This heterogeneous catalytic system was applied for efficient epoxidation of various olefins in the presence of tert-BuOOH in 1,2-dichloroethane under reflux. The catalyst can be reused several times without apparent loss of its catalytic performance.
- Hajian, Robabeh,Tangestaninejad, Shahram,Moghadam, Majid,Mirkhani, Valiollah,Mohammadpoor-Baltork, Iraj,Khosropour, Ahmad Reza
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scheme or table
p. 4134 - 4144
(2012/03/26)
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- Reactivity and kinetic-mechanistic studies of regioselective reactions of rhodium porphyrins with unactivated olefins in water that form β-hydroxyalkyl complexes and conversion to ketones and epoxides
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This article reports on the selective oxidation of unactivated alkenes to ketones and epoxides through the intermediacy of β-hydroxyalkyl rhodium porphyrin complexes which are formed by reactions of terminal alkenes with tetra(p-sulfonatophenyl)porphyrin
- Zhang, Jiadi,Wayland, Bradford B.,Yun, Lin,Li, Shan,Fu, Xuefeng
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scheme or table
p. 477 - 483
(2010/04/04)
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- Regioselective epoxidation of different types of double bonds over large-pore titanium silicate Ti-β
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Regioselective epoxidation of different types of double bonds located within the cyclic and acyclic parts of bulky olefins has been investigated using large-pore titanium silicate Ti-β in the presence of dilute aqueous H 2O2 as oxidant under mild liquid-phase conditions. Our experimental results revealed that side-chain vinylic double bonds are selectively epoxidized than those in the cyclohexene-ring. The epoxidation tendency of various bulky olefins with different positional and/or geometric isomers over Ti-β follows the order: terminal -CC- > ring -CC- ≈ bicyclic ring -CC- > allylic C - H bond. Unlike 4-vinyl-1-cyclohexene, epoxidation of an equimolar mixture of cyclohexene and 1-hexene under identical conditions using Ti-β exhibits completely different selectivity and product distributions. Steric factor and accessibility of reactants to active Ti-sites are responsible for the observed regioselectivity of bulky alkenes.
- Sasidharan, Manickam,Bhaumik, Asim
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experimental part
p. 60 - 67
(2010/12/18)
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