resumo
The complexes Cp'Mo(CO)(2)(eta(3)-C3H5) [Cp' = eta(5)-C5H5 (1), eta(5)-C5H4Me (2), eta(5)-C5Me5 (3)] have been prepared, structurally characterised by X-ray diffraction (2,3), and tested as catalyst precursors for the epoxidation of olefins at 55 degrees C. Complex 1 gave a turnover frequency (TOF) of 310 mol mol(Mo)(-1) h(-1) in the epoxidation of cis-cyclooctene with tert- butylhydroperoxide (TBHP, in decane) as oxidant, and 1,2-epoxycyclooctane was obtained quantitatively within 6 h. A similar result was obtained for complex 2, while the TOF for 3 was about one order of magnitude lower, suggesting a possible activity dependence on the ring substituents. For 1 the use of 1,2-dichloroethane as solvent increased the initial reaction rate to 361 mol mol(Mo)(-1) h(-1), with no decrease in epoxide selectivity. Under these conditions the reaction rates for other olefins increased in the order 1-octene < trans-2-octene < cyclododecene < (R)-(+)-limonene < cis-cyclooctene, and, with the exception of limonene, the corresponding epoxide was the only product. For 1 the selective epoxidation of cis-cyclooctene could also be achieved in aqueous solution, using TBHP or H2O2 as oxidants, which gave epoxide yields of 99% and 27% at 24 h, respectively. The possibility of facilitating catalyst recycling by using ionic liquids as solvents was investigated. (C) 2010 Elsevier B.V. All rights reserved.
palavras-chave
ORGANOMETALLIC CONFORMATIONAL EQUILIBRIA; RING INDENYL ANALOGS; TUNGSTEN COMPLEXES; MIXED-RING; CYCLOALKYL MOIETIES; BRIDGING UNITS; ANSA COMPOUNDS; IONIC LIQUIDS; ALLYL; REACTIVITY
categoria
Chemistry
autores
Neves, P; Pereira, CCL; Paz, FAA; Gago, S; Pillinger, M; Silva, CM; Valente, AA; Romao, CC; 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
Martyn Pillinger
Investigador Principal
Patrícia dos Santos Neves
Investigador Auxiliaragradecimentos
We are grateful to the Fundacao para a Ciencia e a Tecnologia (FCT, Portugal), POCI 2010, OE and FEDER for funding through the project with ref. no. PTDC/QUI/71198/2006. CICECO is acknowledged for financial support through the project entitled