Catalytic olefin epoxidation with cationic molybdenum(VI) cis-dioxo complexes and ionic liquids

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• 作者：S ; ra Gago ; Salete S. Balula ; Só ; nia Figueiredo ; André ; D. Lopes ; Anabela A. Valente ; Martyn Pillinger ; Isabel S. Gonç ; alves
• 关键词：Dioxomolybdenum(VI) ; Tripodal ligands ; Benzimidazole ; Olefin epoxidation ; Ionic liquids
• 刊名：Applied Catalysis A: General
• 出版年：2010
• 出版时间：5 January 2010
• 年：2010
• 卷：372
• 期：1
• 页码：67-72
• 全文大小：148 K

文摘

The complexes [MoO₂Cl(HC(bim)₃)]Y (Y = Cl (1), BF₄ (2) and PF₆ (3)) have been prepared by reaction of MoO₂Cl₂(THF)₂ (for 1) or [MoO₂Cl(THF)₃]Y (for 2 and 3) with the tridentate ligand HC(bim)₃ = tris(benzimidazolyl)methane, and characterized by IR and Raman spectroscopy, and ¹H NMR. The turnover frequencies for the epoxidation of cis-cyclooctene at 55 °C with tert-butyl hydroperoxide (TBHP, in decane) as the oxidant and complexes 1–3 as catalysts are in the range of 70–200 mol mol_Mo⁻¹ h⁻¹. 1,2-Epoxycyclooctane is always the only reaction product for reaction times up to 24 h. With the aim of facilitating the recyclability of the complexes, the ionic liquids (ILs) [BMIM]Y and [BMPy]Y (BMIM = 1-n-butyl-3-methylimidazolium, BMPy = 1-n-butyl-3-methylpyridinium; Y = BF₄ or PF₆) were applied as ionic solvents. The catalytic performance for cyclooctene epoxidation depends strongly on the catalyst solubility in the IL. Of the 12 catalyst/IL mixtures examined, the systems 1/[BMIM]PF₆ and 1/[BMPy]PF₆ exhibit the most favorable reaction rates allied with good recyclability. The 1/[BMIM]PF₆ system was further applied using different oxidants (aqueous TBHP, aqueous H₂O₂ and urea–hydrogen peroxide adduct) and olefins (norbornene, cyclohexene, styrene, α-pinene).