Catalysis Letters, Vol.136, No.3-4, 222-227, 2010
N-Heterocyclic Carbene-Based Molybdenum and Tungsten Complexes as Efficient Epoxidation Catalysts with H2O2 and tert-Butyl Hydroperoxide
The molybdenum and tungsten g eta(3)-allyl dicarbonyl complexes bearing N-heterocyclic carbene (NHC) ligands [M(eta(3)-C3H5)Cl(CO)(2)(bis-NHCBz)] (M = Mo, W; bis-NHCBz = 1,1'-dibenzyl-3,3'-methylenediimidazoline-2,2'-diylidene) have been prepared from the corresponding acetonitrile precursors [M(eta(3)-C3H5)Cl(CO)(2)(NCMe)(2)] by treatment with free carbene. Their catalytic performance in epoxidation of cis-cyclooctene using H2O2 as oxidant has been studied. All complexes can be applied as catalysts precursors in olefin epoxidation displaying 100% selectivity for the formation of cyclooctene oxide. The tungsten acetonitrile precursor [W(eta(3)-C3H5)Cl(CO)(2)(NCMe)(2)] displayed the highest catalytic activity achieving quantitative conversion of epoxide in 30 min. The molybdenum NHC-based compound [Mo(eta(3)-C3H5)Cl(CO)(2)(bis-NHCBz)] displayed higher activity when the epoxidation reaction was performed using H2O2 as oxidant compared to tert-butyl hydroperoxide.