Investigation of a dichlorodioxomolybdenum(VI)-pyrazolylpyridine complex and a hybrid derivative as catalysts in olefin epoxidation

abstract

Treatment of the solvent adduct [MoO2Cl2(THF)(2)] with the ligand 2-(1-pentyl-3-pyrazolyl)pyridine (1, abbreviated as pent-pp) gave the dioxomolybdenum(VI) complex [MoO2Cl2(pent-pp)] (2), which was characterised by elemental analysis, H-1 NMR, FT-IR spectroscopy and single crystal X-ray diffraction (XRD). Reaction of 2 with water in a Teflon-lined stainless steel autoclave at 100 degrees C led to the isolation of a molybdenum oxide/pyrazolylpyridine hybrid material with the composition [Mo2O6(pent-pp)] (3), which was characterised by variable temperature powder XRD, scanning electron microscopy, thermogravimetric analysis, FT-IR and C-13{H-1} CP MAS NMR spectroscopies. Compounds 2 and 3 display high activity and selectivity when used as (pre) catalysts for the epoxidation of cis-cyclooctene at 55 degrees C with tert-butylhydroperoxide as an oxidant. Further catalytic experiments with 3 as a (pre) catalyst were performed using the bio-derived olefins DL-limonene (Lim) and methyl oleate (Ole). The reaction of Lim gave mainly 1,2-epoxy-p-menth-8-ene and 1,2; 8,9-diepoxy-p-menthane in a combined yield of 93% at 97% conversion (6 h), while the reaction of Ole led to 9,10-epoxystearate as the main product in 78% yield at 82% conversion (6 h). The catalytic reactions are homogeneous in nature. Starting with material 3, the oxodiperoxo complex [MoO(O-2)(2)(pent-pp)] (4) was isolated from solution after a catalytic run, suggesting that it is formed from 3 and plays a catalytic role.

keywords

CAMBRIDGE STRUCTURAL DATABASE; BOND-VALENCE PARAMETERS; CRYSTAL-STRUCTURE; DIOXOMOLYBDENUM(VI) COMPLEXES; CYCLOOCTENE EPOXIDATION; MOLYBDENUM(VI) COMPLEX; HYDROTHERMAL SYNTHESIS; EFFICIENT CATALYSTS; ORGANIC-SYNTHESIS; DIOXO COMPLEXES

subject category

Chemistry

authors

Amarante, TR; Neves, P; Paz, FAA; Valente, AA; Pillinger, M; Goncalves, IS

Groups

1 - inorganic functional nanomaterials and organic-inorganic hybrids
4 - biorefineries, biobased materials and recycling

Projects

Desulfurization of diesel using green heterogeneous oxidative catalytic processes (PTDC/EQU-EQU/121677/2010)

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)

acknowledgements

We are grateful to the Fundacao para a Ciencia e a Tecnologia (FCT, project ref. PTDC/EQU-EQU/121677/2010), QREN, FEDER, COMPETE, the European Union (EU), and the Associate Laboratory CICECO (PEst-C/CTM/LA0011/2013) for continued support and funding. The NMR spectrometers are part of the National NMR Network (REDE/1517/RMN/2005), supported by POCI 2010 and the FCT. The FCT is acknowledged for financial support towards the purchase of the single-crystal diffractometer. We thank the FCT and the EU for a post-doctoral grant to P.N. (SFRH/BPD/73540/2010) cofunded by MCTES and the European Social Fund through the program POPH of QREN, and for a PhD grant to T. R. A. (SFRH/BD/64224/2009).