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Heterogeneous oxidation catalysts formed in situ from molybdenum tetracarbonyl complexes and tert-butyl hydroperoxide

Paper ID Volume ID Publish Year Pages File Format Full-Text
41505 45891 2011 7 PDF Available
Title
Heterogeneous oxidation catalysts formed in situ from molybdenum tetracarbonyl complexes and tert-butyl hydroperoxide
Abstract

The tetracarbonyl complexes cis-[Mo(CO)4{2-[3(5)-pyrazolyl]pyridine}] (1) and cis-[Mo(CO)4{ethyl[3-(2-pyridyl)-1-pyrazolyl]acetate}] (2) were obtained in excellent yields by microwave-assisted heating of a mixture of Mo(CO)6 and the organic ligand in toluene at 110 °C for 30 min. Complexes 1 and 2 are air stable, storable catalyst precursors for the epoxidation of olefins by tert-butyl hydroperoxide (TBHP). In situ oxidative decarbonylation of 1 gives the tetranuclear compound [Mo4O12{2-[3(5)-pyrazolyl]pyridine}4] (3). Elemental analysis and infrared data indicate that the oxidation of 2 gives an octameric species with the molecular formula [Mo8O24{ethyl[3-(2-pyridyl)-1-pyrazolyl]acetate}4] (4). The molybdenum oxide/pyrazolylpyridine compounds 3 and 4, which can be readily prepared in very good yields from the parent carbonyls upon reaction with TBHP in n-decane/CH2Cl2 at room temperature, are active and stable heterogeneous catalysts for the epoxidation of cis-cyclooctene (Cy) by TBHP, giving 1,2-epoxycyclooctane as the only product. The highest activity is found for 4: ca. 90% epoxide yield after 6 h reaction at 55 °C. Further experiments confirmed that 2 is an effective catalyst precursor for (i) the epoxidation of Cy by aqueous TBHP, giving the corresponding epoxide as the only product, (ii) the selective epoxidation of R-(+)-limonene by TBHP (in n-decane), and (iii) the selective oxidation of methyl phenyl sulfide to the corresponding sulfoxide by aqueous TBHP or H2O2 at 35 °C.

Graphical abstractFigure optionsDownload full-size imageDownload high-quality image (29 K)Download as PowerPoint slideResearch highlights► Efficient microwave-assisted synthesis of tetracarbonyl-pyrazolylpyridine complexes. ► Oxidative decarbonylation gives molybdenum oxide/pyrazolylpyridine catalysts. ► High selectivities in the epoxidation of olefins and the sulfoxidation of sulfides. ► The heterogeneous catalysts are stable and water-tolerant.

Keywords
Molybdenum; Heterogeneous catalysis; Pyrazolylpyridine ligands; Oxidative decarbonylation; Epoxidation; Sulfoxidation
First Page Preview
Heterogeneous oxidation catalysts formed in situ from molybdenum tetracarbonyl complexes and tert-butyl hydroperoxide
Publisher
Database: Elsevier - ScienceDirect
Journal: Applied Catalysis A: General - Volume 395, Issues 1–2, 15 March 2011, Pages 71–77
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Catalysis