Influence of Cyclodextrins on Catalytic Olefin Epoxidation with Metal–Carbonyl Compounds. Crystal Structure of the TRIMEB Complex with CpFe(CO)2Cl

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• 作者：Salete S. Balula ; Ana C. Coelho ; Susana S. Braga ; Alan Hazell ; Anabela A. Valente ; Martyn Pillinger ; Joã ; o D. Seixas ; Carlos C. Romã ; o ; Isabel S. Gonç ; alves
• 刊名：Organometallics
• 出版年：2007
• 出版时间：December 31, 2007
• 年：2007
• 卷：26
• 期：27
• 页码：6857 - 6863
• 全文大小：615K
• 年卷期：v.26,no.27(December 31, 2007)
• ISSN：1520-6041

文摘

The cyclopentadienyl metal–carbonyls CpFe(CO)₂Cl and CpMo(CO)₃Cl, and their 1:1 inclusion complexes with β-cyclodextrin (β-CD) and permethylated β-CD (TRIMEB), were prepared, and the TRIMEB adduct with CpFe(CO)₂Cl was structurally characterized by single-crystal X-ray diffraction. The complex crystallizes in the orthorhombic space group P2₁2₁2₁, with a = 11.189(3) Å, b = 25.149(6) Å, c = 28.964(7) Å and Z = 4 formula units. One CpFe(CO)₂Cl guest molecule, disordered over two sites, is completely enclosed in the TRIMEB cavity. The cyclodextrin molecules pack in columns parallel to the crystallographic a axis and make an angle of 33.6° with the bc plane. The oxidative decarbonylation of the free and encapsulated complexes by aqueous tert-butylhydroperoxide (t-BuOOH) or aqueous H₂O₂ was studied at room temperature by quantifying the CO/CO₂ liberated in the gas phase. When CpMo(CO)₃Cl is encapsulated in CDs, the extent of the decarbonylation by t-BuOOH is reduced. The use of H₂O₂ as oxidant modifies the reactivity in an unexpected fashion. Thus, the β-CD adduct almost totally resists oxidation by H₂O₂, whereas the TRIMEB adduct decarbonylates faster than the nonincluded complex during the early stages of the reaction. CpMo(CO)₃Cl and the two inclusion complexes were examined as catalyst precursors for the epoxidation of cyclooctene at 295 or 328 K, using t-BuOOH in decane or water, or aqueous H₂O₂, as oxidants. Although the free complex is essentially inactive as a catalyst precursor with aqueous H₂O₂, the introduction of CDs to the system instills significant catalytic activity, with cyclooctene oxide being the only observed reaction product.