New chloro and triphenylsiloxy derivatives of dioxomolybdenum(VI) chelated with pyrazolylpyridine ligands: Catalytic applications in olefin epoxidation
authors Bruno, SM; Pereira, CCL; Balula, MS; Nolasco, M; Valente, AA; Hazell, A; Pillinger, M; Ribeiro-Claro, P; Goncalves, IS
nationality International
journal JOURNAL OF MOLECULAR CATALYSIS A-CHEMICAL
author keywords epoxidation; homogeneous catalysis; molybdenum; pyrazolylpyridine ligands; dioxoinolybdenum(VI) complexes
keywords STRUCTURAL-CHARACTERIZATION; MOLECULAR-STRUCTURE; CRYSTAL-STRUCTURES; DIOXO COMPLEXES; MOLYBDENUM; REACTIVITY; OXIDATIONS; PRECURSORS; ALKOXIDES; SILICA
abstract Dioxomolybdenum(VI) complexes of general formula [MoO2X2L2] (X=Cl, OSiPh3; L-2 =2-(1-butyl-3-pyrazolyl)pyridine, ethyl [3-(2-pyridyl)-1-pyrazolyl]acetate) were prepared and characterised by H-1 NMR, IR and Raman spectroscopy. The assignment of the vibrational spectra was supported by ab initio calculations. A single crystal X-ray diffraction study of the complex [MoO2Cl2{ethyl[3-(2-pyridyl)-1-pyrazolyl]acetate}] showed that the compound is monomeric and crystallises in the tetragonal system with space group P4(1). The four complexes are active and selective catalysts for the liquid-phase epoxidation of olefins by tert-butylhydroperoxide. Selectivities to the corresponding epoxides were mostly 100% (for conversions of at least 34%) for the substrates cyclooctene, cyclododecene, I-octene, trans-2-octene and (R)-(+)-limonene. For styrene epoxidation. the corresponding diol was also formed in significant quantities. The turnover frequencies for cyclooctene epoxidation at 55 degrees C were around 340 mol mol(Mo)(-1) h(-1) for the chloro complexes and 160 mol mol(Mo)(-1) h(-1) for the triphenylsiloxy complexes. The addition of co-solvents (1,2-dichloroethane or n-hexane) had a detrimental effect on catalytic activities. Kinetic studies for the two complexes bearing the ligand ethyl[3(2-pyridyl)-1-pyrazolyl]acetate revealed an apparent first order dependence of the initial rate of cyclooctene conversion with respect to cyclooctene or oxidant concentration. (c) 2006 Elsevier B.V. All rights reserved.
publisher ELSEVIER SCIENCE BV
issn 1381-1169
year published 2007
volume 261
issue 1
beginning page 79
ending page 87
digital object identifier (doi) 10.1016/j.molcata.2006.07.064
web of science category Chemistry, Physical
subject category Chemistry
unique article identifier WOS:000243505200013

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