Synthesis and characterization of CpMo(CO)3(CH2–pC6H4–CO2CH3) and its inclusion compounds with methylated cyclodextrins. Applications in olefin epoxidation catalysis

The cyclopentadienyl molybdenum tricarbonyl complex CpMo(CO)3(CH2–pC6H4–CO2CH3) (1) (Cp = η5-C5H5) and its 1:1 inclusion complexes with heptakis(2,6-di-O-methyl)-β-cyclodextrin (1@DIMEB) and heptakis(2,3,6-tri-O-methyl)-β-cyclodextrin (1@TRIMEB) were prepared and characterized by elemental and thermogravimetric analyses, powder X-ray diffraction, NMR, FT-IR and Raman spectroscopy. All three compounds were investigated as catalyst precursors for olefin epoxidation using cis-cyclooctene (Cy) as a model substrate, a reaction temperature of 55 °C, and different types of oxidants (tert-butylhydroperoxide in decane (TBHPdec) or in water (TBHPaq), and aqueous hydrogen peroxide). With the aim of facilitating recycling of the homogeneous catalytic systems, different solvent mixtures were tested: biphasic liquid–liquid solvent systems [(water, glycerol, ionic liquid)–(n-hexane, α,α,α-trifluorotoluene (TFT), iso-butyl methyl ketone)], and in some cases no cosolvent was added. Excellent epoxide selectivity (100%) was observed for all tested catalytic systems. An example of an interesting catalytic system is that of 1@TRIMEB/TBHPaq/TFT/H2O since the catalyst can be easily separated in the form of an aqueous solution, by decantation, from the organic phase containing the reaction products and recycled.

The complex CpMo(CO)3(CH2–pC6H4–CO2CH3) and its inclusion complexes with heptakis(2,6-di-O-methyl)-β-cyclodextrin (CD) and heptakis(2,3,6-tri-O-methyl)-β-CD were prepared and characterized, and investigated as catalyst precursors for the epoxidation of cis-cyclooctene at 55 °C. Different types of oxidants (tert-butylhydroperoxide or H2O2) and biphasic liquid–liquid solvent systems were used with the aim of facilitating catalyst recycling.Figure optionsDownload as PowerPoint slideHighlights
► Synthesis and characterization of CpMo(CO)3(CH2–pC6H4–CO2CH3) (1).
► Synthesis of 1:1 inclusion compounds between 1 and methylated cyclodextrins.
► Complex 1 and its TRIMEB adduct are effective precatalysts for cyclooctene epoxidation.
► Aqueous tert-butylhydroperoxide and hydrogen peroxide can be used as oxidants.
► Biphasic liquid–liquid systems were studied, aiming to facilitate catalyst recycling.