resumo
The ligand N-(n-propyl)-2-pyridylmethanimine (pyim) and an immobilized analogue of this ligand (pyim-MTS) were prepared by the condensation reaction of 2-pyridinecarboxaldehyde with either n-propylamine or 3-aminopropyl groups covalently attached to a micelle-templated silica (MTS). Free and immobilized dioxomolybdenum(VI) complexes of the type MoO2Cl2(L-1) (L-1 = pyim (1), pyim-MTS) were then prepared by treatment of the organic ligand or ligand-silica with the solvent adduct MoO2Cl2(THF)(2). MoO2Cl2(pyim) (1) is a highly active catalyst for the epoxidation of olefins (cyclooctene (Cy), cyclododecene, 1-octene, trans-2-octene, R-(+)-limonene) at 55 degrees C using tert-butylhydroperoxide (TBHP) as the oxidant under solvent-free conditions, giving the corresponding epoxides as the only reaction products. A turnover frequency of 1855 mol mol(Mo)(-1) h(-1) was measured for the epoxidation of Cy, and the epoxide (CyO) was formed quantitatively within 4.5 h. The MTS-supported complex was less active, and exhibited temperature-dependent leaching of active species. As an alternative approach to facilitating catalyst recycling, complex 1 was investigated with the ionic liquid (IL) 1-butyl-3-methylimidazolium tetrafluoroborate as solvent. The 1/IL phase could be reused, giving ca. 95% CyO yield in each run. (C) 2012 Elsevier B.V. All rights reserved.
palavras-chave
SUPPORTED PALLADIUM CATALYST; ORDERED MESOPOROUS SILICA; TERT-BUTYL HYDROPEROXIDE; BIDENTATE LEWIS-BASE; DIOXOMOLYBDENUM(VI)-BIPYRIDINE COMPLEXES; CYCLOOCTENE EPOXIDATION; MOLYBDENUM COMPLEXES; LIGANDS; PERFORMANCE; PRECURSORS
categoria
Chemistry
autores
Balula, SS; Bruno, SM; Gomes, AC; Valente, AA; Pillinger, M; Goncalves, IS; Macquarrie, DJ; Clark, JH
nossos autores
Ana Catarina Costa Gomes Alves
Investigador Auxiliar
Anabela Tavares Aguiar Valente
Investigador Principal
Isabel Maria de Sousa Gonçalves
Professor associado
Martyn Pillinger
Investigador Principal
Sofia M. Bruno
Investigador Auxiliaragradecimentos
We are grateful to the Fundacao para a Ciencia e a Tecnologia (FCT), the Programa Operacional Ciencia e Inovacao (POCI) 2010, Orcamento do Estado (OE), and Fundo Europeu de Desenvolvimento Regional (FEDER) for funding. The FCT and the European Social Fund are acknowledged for a post-doctoral Grant to S.M.B. (SFRH/BPD/46473/2008). CICECO is acknowledged for financial support (including a post-doctoral research Grant to A.C.G.) through the project entitled