Epoxidation of cyclooctene using soluble or MCM-41-supported molybdenum tetracarbonyl–pyridylimine complexes as catalyst precursors

Abstract

The ligand N-(n-propyl)-2-pyridylmethanimine (pyim) and an immobilised analogue of this ligand (MCM-41-pyim) were prepared by the condensation reaction of 2-pyridinecarboxaldehyde with either propylamine or aminopropyl groups covalently attached to the ordered mesoporous silica MCM-41. Free and immobilised tetracarbonyl complexes of the type cis-[Mo(CO) 4(L)] ( L = pyim ( 1), MCM-41-pyim) were then prepared by microwave-assisted heating of a mixture of Mo(CO) 6 and the organic ligand or ligand-silica in toluene at 110 °C for 30–45 min. The products were characterised by NMR spectroscopy ( 1H, 13C and 29Si, in solution and in the solid state), elemental analysis, N 2 adsorption, and FT-IR spectroscopy. When used as catalyst precursors for the epoxidation of cis-cyclooctene by tert-butylhydroperoxide at 55 °C (1 mol% catalyst (Mo), no additional co-solvent), 1,2-epoxy-cyclooctane was obtained as the only reaction product in quantitative yield after 5 h for 1 and 36% yield after 24 h for the supported complex. The use of the ionic liquid (IL) 1-butyl-3-methylimidazolium tetrafluoroborate as co-solvent led to lower catalytic activities (epoxide selectivity was always 100%) but allowed the catalyst/IL mixtures (homogeneous mixture for IL+ 1 and a biphasic solid + IL system for IL+MCM-41-pyim/Mo) to be easily recovered and reused in subsequent runs without loss of catalytic performance.