title: Dioxomolybdenum(VI) complexes with pyrazole based aryloxide ligands: synthesis, characterization and application in epoxidation of olefins.
abstract: Synthesis, characterization, and epoxidation chemistry of four new dioxomolybdenum(VI) complexes [MoO(2)(L)(2)] (1-4) with aryloxide-pyrazole ligands L = L1-L4 is described. Catalysts 1-4 are air and moisture stable and easy to synthesize in only three steps in good yields. All four complexes are coordinated by the two bidentate ligands in an asymmetric fashion with one phenoxide and one pyrazole being trans to oxo atoms, respectively. This is in contrast to the structure found for the related aryloxide-oxazoline coordinated Mo(VI) dioxo complex 5. This was confirmed by the determination of the molecular structures of complexes 1-3 by X-ray diffraction analyses. Compounds 1-4 show high catalytic activities in the epoxidation of various olefins. Cyclooctene (S1) is converted to its epoxide with high activity, whereas the epoxidation of styrene (S2) is unselective. Internal olefins (S3 and S4) are also acceptable substrates, as well as the very challenging olefin 1-octene (S5). Catalyst loading can be reduced to 0.02 mol % and the catalyst can be recycled up to ten times without significant loss of activity. Supportive DFT calculations have been carried out in order to obtain deeper insights into the electronic situation around the Mo atom.
authors: Institute of Chemistry, Karl-Franzens-University Graz, Stremayrgasse 16, 8010 Graz, Austria.
authors: Jörg A
authors: JA
authors: Schachner
authors: Pedro
authors: P
authors: Traar
authors: Chris
authors: C
authors: Sala
authors: Michaela
authors: M
authors: Melcher
authors: Bastian N
authors: BN
authors: Harum
authors: Alexander F
authors: AF
authors: Sax
authors: Manuel
authors: M
authors: Volpe
authors: Ferdinand
authors: F
authors: Belaj
authors: Nadia C
authors: NC
authors: Mösch-Zanetti
mesh_terms: D000475:Alkenes / Q000737:chemistry*; D004852:Epoxy Compounds / Q000737:chemistry; D008024:Ligands; D008958:Models, Molecular; D015394:Molecular Structure; D008982:Molybdenum / Q000737:chemistry*; D009942:Organometallic Compounds / Q000138:chemical synthesis* / Q000737:chemistry*; D010087:Oxides / Q000737:chemistry*; D010100:Oxygen / Q000737:chemistry; D011720:Pyrazoles / Q000737:chemistry*; D011789:Quantum Theory
chemical_list: D000475:Alkenes; D004852:Epoxy Compounds; D008024:Ligands; D009942:Organometallic Compounds; D010087:Oxides; D011720:Pyrazoles; C031280:pyrazole; D008982:Molybdenum; D010100:Oxygen