• Valente, Anabela A.
• Gonçalves, Isabel S.
• Klinowski, Jacek
• Lage Pereira, Cláudia
• Abrantes, Marta
• Paz, Filipe A. Almeida
• Pillinger, Martyn
• Rodrigues, Alírio E.
• Gago, Sandra

Abstract

<p>The complex [(N-benzyloxycarbonylprolyl)cyclopentadienyl]-Mo(CO)₃Me was prepared by the reaction of the amino acid-functionalized cyclopentadienyl-lithium reagent with Mo(CO)₆, and subsequent methylation with CH₃I. The complex was characterized by FTIR, ¹H and ¹³C NMR, and elemental analysis. A single-crystal X-ray diffraction study showed that the complex is chiral, crystallizing in the orthorhombic P2₁2₁2₁ space group with the Flack parameter refining to -0.007(16), which unequivocally confirms the presence of an enantiomerically pure compound. The complex was examined as a catalyst precursor in the liquid-phase epoxidation of trans-β-methylstyrene at 280-330 K, using either tert-butylhydroperoxide (tert-BuOOH), cumylhydroperoxide or urea-hydrogen peroxide adduct as oxidant, and, optionally, a co-solvent. With chloroform and tert-BuOOH, the catalytic activity surpasses that previously reported for chiral complexes of the type CpMo(CO)₃X, giving the epoxide isomers ((R,R)-(+) and (S,S)-(-)-1-phenylpropylene oxide) in excellent selectivity, albeit with negligible enantiomeric excess. FTIR spectroscopy showed that the oxidative decarbonylation of the tricarbonyl complex with tert-BuOOH is fast under the reaction conditions used, and that the structural integrity of the amino acid-functionalized cyclopentadienyl group is retained during this process. The use of the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate as a solvent for the catalyst generates a biphasic liquid-liquid reaction system that enables, at the end of a catalytic cycle, the separation and reutilization of the catalyst.</p>

Topics

• impedance spectroscopy
• compound
• molybdenum
• phase
• x-ray diffraction
• Hydrogen
• Lithium
• Nuclear Magnetic Resonance spectroscopy
• space group
• elemental analysis