Molybdenum(VI) catalysts obtained from eta(3)-allyl dicarbonyl precursors: Synthesis, characterization and catalytic performance in cyclooctene epoxidation

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The oxidative decarbonylation of the eta(3)-allyl dicarbonyl complexes [Mo(eta(3)-C3H5)Cl(CO)(2)(L)] (L = 2,2'-bipyridine (bipy) (1), 4,4'-di-tert-butyl-2,2'-bipyridine (di-tBu-bipy) (2)) by reaction with aqueous tert-butylhydroperoxide (TBHP) or H2O2 gave the following compounds in good to excellent yields: the oxo-bridged dimers [MoO2Cl(L)](2)O (L = bipy (3), di-tBu-bipy (6)) using TBHP(10 equiv.)/CH3CN/r.t.; the molybdenum oxide/bipyridine hybrid material {[MoO3(bipy)][MoO3(H2O)]}(n) (4) and the octanuclear complex [Mo8O24(di-tBu-bipy)(4)] (7) using TBHP(50 equiv.)/H2O/70 degrees C; the oxodiperoxo complexes MoO(O-2)(2)(L) (L = bipy (5), di-tBu-bipy (8)) using H2O2(10 equiv.)/CH3CN/r.t. The structure of 7.x (solvent) (where solvent = CH2Cl2 and/or diethyl ether) was determined by single crystal X-ray diffraction. Despite possessing the same windmill-type complex as that described previously for 7.10CH(2)Cl(2), the crystal structure of 7.x(solvent) is unique due to differences in the crystal packing. Compounds 1-8 were examined as catalysts or catalyst precursors for the epoxidation of cyclooctene using aqueous TBHP or H2O2 as oxidant at 55 or 70 degrees C. Reactions were performed without co-solvent or with the addition of water, ethanol or acetonitrile. Cyclooctene oxide was always the only reaction product. Solids recovered after 24 h reaction at 70 degrees C were identified by FT-IR spectroscopy as the hybrid 4 from (1,3-5)/TBHP, complex 5 from (1,3-5)/H2O2, and complex 8 from (2,6-8)/H2O2. With TBHP as oxidant, the highest epoxide yields (for 24 h reaction at 70 degrees C) were obtained using excess H2O as solvent (28-38% for 1,3-5; 87-98% for 2,6-8), while with H2O2 as oxidant, the highest epoxide yields were obtained using CH3CN as solvent (54-81% for 3-8).
Original languageUnknown
Pages (from-to)3474-3484
JournalDalton Transactions
Issue number12
Publication statusPublished - 1 Jan 2012

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