Chemistry and Catalytic Activity of Molybdenum(VI)-Pyrazolylpyridine Complexes in Olefin Epoxidation. Crystal Structures of Monomeric Dioxo, Dioxo-渭-oxo, and Oxodiperoxo Derivatives

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• 作者：Ana C. Coelho ; Mariela Nolasco ; Salete S. Balula ; Margarida M. Antunes ; Cla虂udia C. L. Pereira ; Filipe A. Almeida Paz ; Anabela A. Valente ; Martyn Pillinger ; Paulo Ribeiro-Claro ; Jacek Klinowski ; Isabel S. Gonc抬alves
• 刊名：Inorganic Chemistry
• 出版年：2011
• 出版时间：January 17, 2011
• 年：2011
• 卷：50
• 期：2
• 页码：525-538
• 全文大小：1119K
• 年卷期：v.50,no.2(January 17, 2011)
• ISSN：1520-510X

文摘

The dioxomolybdenum(VI) complexes [MoO₂Cl₂(PzPy)] (1) and [MoO₂(OSiPh₃)₂(PzPy)] (5) (PzPy = 2-[3(5)-pyrazolyl]pyridine) were synthesized and characterized by vibrational spectroscopy, with assignments being supported by DFT calculations. Complex 5 was additionally characterized by single crystal X-ray diffraction. Recrystallization of 1 under different conditions originated crystal structures containing either the mononuclear [MoO₂Cl₂(PzPy)] complex co-crystallized with 2-[3(5)-pyrazolyl]pyridinium chloride, binuclear [Mo₂O₄(渭₂-O)Cl₂(PzPy)₂] complexes, or the oxodiperoxomolybdenum(VI) complex [MoO(O₂)₂Cl(PzPyH)], in which a 2-[3(5)-pyrazolyl]pyridinium cation weakly interacts with the Mo^VI center via a pyrazolyl N-atom. The crystal packing in the different structures is mediated by a variety of supramolecular interactions: hydrogen bonding involving the pyridinium and/or pyrazolyl N鈭扝 groups, weak CH路路路O and CH路路路蟺 contacts, and strong 蟺鈭捪€ stacking. Complexes 1 and 5 are moderately active catalysts for the epoxidation of cis-cyclooctene at 55 掳C using tert-butylhydroperoxide as oxidant, giving 1,2-epoxycyclooctane as the only reaction product. Insoluble materials were recovered at the end of the first catalytic runs and characterized by IR spectroscopy, elemental analysis, scanning electron microscopy (SEM)-energy dispersive spectroscopy (EDS), and powder X-ray diffraction. For complex 5 the loss of the triphenylsiloxy ligands during the catalytic run resulted in the formation of a tetranuclear complex, [Mo₄O₈(渭₂-O)₄(PzPy)₄]. The recovered solids could be used as efficient heterogeneous catalysts for the epoxidation of cyclooctene, showing no loss of catalytic performance between successive catalytic runs.