resumo
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.
palavras-chave
BOND-VALENCE PARAMETERS; CRYSTAL-STRUCTURE; TRIS(PYRAZOLYL)METHANE LIGANDS; OLEFIN EPOXIDATION; WATER CLUSTER; FRAMEWORK; COORDINATION; FUNCTIONALITY; CHEMISTRY; NETWORKS
categoria
Chemistry
autores
Neves, P; Gago, S; Balula, SS; Lopes, AD; Valente, AA; Cunha-Silva, L; Paz, FAA; Pillinger, M; Rocha, J; Silva, CM; Goncalves, IS
nossos autores
Anabela Tavares Aguiar Valente
Investigador Principal
Carlos Manuel Silva
Professor associado
Filipe Alexandre Almeida Paz
Investigador Principal
Isabel Maria de Sousa Gonçalves
Professor associado
João Rocha
Prof. Catedrático
Martyn Pillinger
Investigador Principal
Patrícia dos Santos Neves
Investigador AuxiliarProjectos
Nanogotas de Água em Materiais Microporosos e Híbridos Orgânicos-Inorgânicos (PTDC/QUI/65805/2006)
agradecimentos
We are grateful to the Fundacao para a Ciencia e a Tecnologia (FCT), the Programa Operacional