67663-02-9Relevant articles and documents
Mo Schiff base-tungstate ionic hybrid with enhanced heterogeneous catalytic activity for epoxidation reactions
Fan, Weizheng,Leng, Yan,Liu, Jian,Jiang, Pingping,Zhao, Jiwei
, p. 173 - 179 (2015)
A novel metal Schiff base-tungstate ionic hybrid (Mo-MimAM-WO4) was prepared by anion-exchange of Mo Schiff base functionalized imidazole ionic liquid with sodium tungstate. The resulting hybrid catalyst was fully characterized by 1H NMR, FT-IR, XRD, SEM, TGA, and XPS, and its catalytic activity was studied for the epoxidation of alkenes using aqueous H2O2 as the oxidant. The catalyst was found to be highly efficient and showed higher catalytic activity than its corresponding homogeneous and heterogeneous analogues Mo-MimAM and Na2WO4. After reaction, the catalyst can be easily recovered by filtration and reused for the next run. The synergistic effect between Mo Schiff base complex and tungstate is revealed to be responsible for the catalyst's excellent performance in epoxidation.
New heptacoordinate tungsten(II) complexes with α-diimine ligands in the catalytic oxidation of multifunctional olefins
Vasconcellos-Dias, Maria,Nunes, Carla D.,Félix, Vítor,Brand?o, Paula,Calhorda, Maria José
, (2021/02/26)
New tungsten(II) and molybdenum(II) heptacoordinate complexes [MX2(CO)3(LY)] (MXLy: M = W, Mo; X = Br, I; LY = C5H4NCY = N(CH2)2CH3 with Y = H (L1), Me (L2), Ph (L3)) were synthesized and characterized by spectroscopic techniques and elemental analysis. The two tungsten complexes WXL1 (X = Br, I) were also structurally characterized by single crystal X-ray diffraction. The metal coordination environment is in both a distorted capped octahedron. The complexes with L1 and L2 ligands were grafted in MCM-41, after functionalization of the ligands with a Si(OEt)3 group. The new materials were characterized by elemental analysis, N2 adsorption isotherms, 29Si MAS and 13C MAS NMR. The tungsten(II) complexes and materials were the first examples of this type reported. All complexes and materials were tested as homogeneous and heterogeneous catalysts in the oxidation of multifunctional olefins (cis-hex-3-en-1-ol, trans-hex-3-en-1-ol, geraniol, S-limonene, and 1-octene), with tert-butyl hydroperoxide (TBHP) as oxidant. The molybdenum(II) catalyst precursors are in general very active, reaching 99% conversion and 100% selectivity in the epoxidation of trans-hex-3-en-1-ol. Their performance is comparable with that of the [Mo(η3-C3H5)X(CO)2(LY)] complexes, but it increases with immobilization. On the other hand, most of the W(II) complexes display an activity similar or inferior to that of the Mo(II) analogues and it decreases after they are supported in MCM-41. DFT calculations show that tungsten complexes and iodide ligands are more easily oxidized from M(II) to M(VI) than molybdenum ones, while the energies of relevant species in the catalytic cycle are very similar for all complexes, making the theoretical rationalization of experimental catalytic data difficult.
New molybdenum(II) complexes with α-diimine ligands: Synthesis, structure, and catalytic activity in olefin epoxidation
Vasconcellos-Dias, Maria,Marreiros, Jo?o,Sales, Rita,Félix, Vitor,Brand?o, Paula,Nunes, Carla D.,José Calhorda, Maria
, (2019/02/10)
Three new complexes [Mo(η3-C3H5)Br(CO)2{iPrN=C(R)C5H4N}], where R = H (IMP = N-isopropyl 2-iminomethylpyridine), Me, and Ph, were synthesized and characterized, and were fluxional in solution. The most interesting feature was the presence, in the crystal structure of the IMP derivative, of the two main isomers (allyl and carbonyls exo), namely the equatorial isomer with the Br trans to the allyl and the equatorial with the Br trans to one carbonyl, the position trans to the allyl being occupied by the imine nitrogen atom. For the R = Me complex, the less common axial isomer was observed in the crystal. These complexes were immobilized in MCM-41 (MCM), following functionalization of the diimine ligands with Si(OEt)3, in order to study the catalytic activity in olefin epoxidation of similar complexes as homogeneous and heterogeneous catalysts. FTIR,13C- and29Si-NMR, elemental analysis, and adsorption isotherms showed that the complexes were covalently bound to the MCM walls. The epoxidation activity was very good in both catalysts for the cis-cyclooctene and cis-hex-3-en-1-ol, but modest for the other substrates tested, and no relevant differences were found between the complexes and the Mo-containing materials as catalysts.
