abstract
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).
keywords
TERT-BUTYL HYDROPEROXIDE; BOND-VALENCE PARAMETERS; PI-ALLYL COMPLEXES; CRYSTAL-STRUCTURE; TUNGSTEN COMPLEXES; OLEFIN EPOXIDATION; NITROGEN DONOR; OXO MOLYBDENUM; LIGANDS; MO
subject category
Chemistry
authors
Gamelas, CA; Gomes, AC; Bruno, SM; Paz, FAA; Valente, AA; Pillinger, M; Romao, CC; Goncalves, IS
our authors
acknowledgements
We are grateful to the Fundacao para a Ciencia e a Tecnologia (FCT), the Programa Operacional Ciencia e Inovacao (POCI) 2010, Orcamento do Estado (OE), and Fundo Europeu de Desenvolvimento Regional (FEDER) for general funding, and for financial support (FCT) towards the purchase of the single-crystal diffractometer. The NMR spectrometers are part of The National NMR Network (REDE/1517/RMN/2005), supported by POCI 2010 and the FCT. The FCT and the European Social Fund are acknowledged for a post-doctoral grant to S. M. B (SFRH/BPD/46473/2008). CICECO is acknowledged for financial support (including a post-doctoral research grant to A. C. G.) through the project entitled