Journal
INORGANIC CHEMISTRY
Volume 50, Issue 8, Pages 3490-3500Publisher
AMER CHEMICAL SOC
DOI: 10.1021/ic102456z
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Funding
- Fundacao para a Ciencia e a Tecnologia (FCT)
- Programa Operacional Ciencia e Inovacao
- Orcamento do Estado (OE)
- Fundo Europeu de Desenvolvimento Regional (FEDER) [PTDC/QUI/71198/2006, PTDC/QUI/65805/2006]
- Fundação para a Ciência e a Tecnologia [PTDC/QUI/71198/2006, PTDC/QUI/65805/2006] Funding Source: FCT
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The complex [MoO2Cl{HC(3,5-Me(2)pz)(3)}]BF4 (1) (HC(3,5-Me(2)pz)(3) = tris(3,5-dimethyl-1-pyrazolyl)methane) has been prepared and examined as a catalyst for epoxidation of olefins at 55 degrees C using tert-butyl hydroperoxide (TBHP) as the oxidant. For reaction of cis-cyclooctene, epoxycyclooctane is obtained quantitatively within 5 h when water is rigorously excluded from the reaction mixture. Increasing amounts of water in the reaction mixture lead to lower activities (without affecting product selectivity) and transformation of 1 into the trioxidomolybdenum(VI) complex [{HC(3,5-Me(2)pz)(3)}MoO3] (4). Complex 4 was isolated as a microcrystalline solid by refluxing a suspension of 1 in water. The powder X-ray diffraction pattern of 4 can be indexed in the orthorhombic Pnma system, with a = 16.7349(5) angstrom, b = 13.6380(4) angstrom, and c = 7.8513(3) angstrom. Treatment of 1 in dichloromethane with excess TBHP led to isolation of the symmetrical [Mo2O4(mu(2)-O){HC(3,5-Me(2)pz)(3)}(2)}(BF4)(2) (2) and unsymmetrical [Mo2O3(O-2)(2)(mu(2)-O)(H2O){HC(3,5-Me(2)pz)(3)}] (3) oxido-bridged dimers, which were characterized by single-crystal X-ray diffraction. Complex 2 displays the well-known (Mo2O5)(2+) bridging structure where each dioxidomolybdenum(VI) center is coordinated to three N atoms of the organic ligand and one mu(2)-bridging O atom. The unusual complex 3 comprises dioxido and oxidodiperoxo molybdenum(VI) centers linked by a mu(2)-bridging O atom, with the former center being coordinated to the tridentate N-ligand. The dinuclear complexes exhibit a similar catalytic performance to that found for mononuclear 1. For complexes 1 and 2 use of the ionic liquids (ILs) 1-butyl-3-methylimidazolium tetrafluoroborate and N-butyl-3-methylpyridinium tetrafluoroborate as solvents allowed the complexes to be completely dissolved, and in each case the catalyst and IL could be recycled and reused without loss of activity.
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