N-Heterocyclic Carbene-Based Molybdenum and Tungsten Complexes as Efficient Epoxidation Catalysts with H₂O₂ and tert-Butyl Hydroperoxide

Author： Krishna Mohan Kandepi V. Cardoso João Royo Beatriz

Publisher： Springer Publishing Company

ISSN： 1011-372X

Source： Catalysis Letters, Vol.136, Iss.3-4, 2010-06, pp. : 222-227

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Abstract

The molybdenum and tungsten η³-allyl dicarbonyl complexes bearing N-heterocyclic carbene (NHC) ligands [M(η³-C₃H₅)Cl(CO)₂(bis-NHC^Bz)] (M = Mo, W; bis-NHC^Bz = 1,1′-dibenzyl-3,3′-methylenediimidazoline-2,2′-diylidene) have been prepared from the corresponding acetonitrile precursors [M(η³-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(η³-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(η³-C₃H₅)Cl(CO)₂(bis-NHC^Bz)] displayed higher activity when the epoxidation reaction was performed using H₂O₂ as oxidant compared to tert-butyl hydroperoxide.