Catalytic olefin epoxidation with a carboxylic acid-functionalized cyclopentadienyl molybdenum tricarbonyl complex

resumo

The complex CpMo(CO)(3)CH2COOH (1) (Cp = eta(5)-C5H5) has been examined as a precatalyst for the epoxidation of cis-cyclooctene and alpha-pinene using tert-butylhydroperoxide (TBHP) as oxidant. A high turnover frequency of ca. 600 mol mol(Mo)(-1) h(-1) was achieved in the epoxidation of cyclooctene, giving the epoxide as the only reaction product. With alpha-pinene as substrate, the added-value products a-pinene oxide and campholenic aldehyde were obtained. Two different approaches to facilitate catalyst recovery and reuse were explored: (1) use of an ionic liquid (IL) as solvent, and (2) intercalation of 1 in a Zn, Al layered double hydroxide (LDH) by a direct synthesis (coprecipitation) route. Characterization of the LDH by powder X-ray diffraction, thermogravimetric analysis, FT-IR and C-13 CP MAS NMR spectroscopies showed that the CpMo(CO)(3)CH2COO- anions intercalate in a bilayer arrangement, resulting in an interlayer spacing of 20.7 angstrom. In the epoxidation of cyclooctene, catalytic activity in the first batch run was very high for the catalyst/IL mixture and moderate for the LDH. Characterization of the LDH after catalysis indicated that nearly complete oxidative decarbonylation of supported complexes had occurred (by reaction with TBHP), resulting in the presence of immobilized oxomolybdenum species. However, catalytic activities for both the recovered LDH and catalyst/IL decreased in consecutive runs, due in part to progressive removal of active species during either the catalytic reaction (for the LDH) or the solvent extraction/work-up (for the catalyst/IL mixture). (C) 2013 Elsevier B.V. All rights reserved.

palavras-chave

LAYERED DOUBLE HYDROXIDE; ETA(5)-CYCLOPENTADIENYL MOLYBDENUM; TUNGSTEN COMPLEXES; CYCLOALKYL MOIETIES; INCLUSION-COMPOUNDS; CARBONYL-COMPLEXES; CRYSTAL-STRUCTURE; OXO-MOLYBDENUM; BRIDGING UNITS; ANSA COMPOUNDS

categoria

Chemistry

autores

Gomes, AC; Bruno, SM; Abrantes, M; Magalhaes, CIR; Goncalves, IS; Valente, AA; Pillinger, M

Grupos

G1 - Materiais Porosos e Nanossistemas
G4 - Materiais Renováveis e Economia Circular

Projectos

Centre for Research in Ceramics and Composite Materials - CICECO (LA0011: 2013-2014) (PEst-C/CTM/LA0011/2013)

PTNMR - Portuguese Nuclear Magnetic Resonance Network (REDE/1517/RMN/2005)

Use of molecular containers to modify metallocene-based catalysts (PTDC/QEQ-SUP/1906/2012)

agradecimentos

We are grateful to the Fundacao para a Ciencia e a Tecnologia (FCT), QREN, Fundo Europeu de Desenvolvimento Regional (FEDER), COMPETE, the European Union, the Associate Laboratory CICECO (PEst-C/CTM/LA0011/2013) and CQE (PEst-OE/QUI/UI0100/2013) for continued support and funding, including the R&D Project PTDC/QEQ-SUP/1906/2012 and the research grant BPD/UI89/4864/2013 (A. C. G.) provided within this project. The NMR spectrometers are part of The National NMR Network (REDE/1517/RMN/2005), supported by POCI 2010 and the FCT. The authors also thank the Portuguese NMR Network (IST-UTL Center) (RECI/QEQ-QIN/0189/2012) for providing access to the NMR facilities. The FCT and the European Union are acknowledged for a post-doctoral grant to S. M. B (SFRH/BPD/46473/2008) cofunded by MEC and the European Social Fund through the program POPH of QREN.