Chemistry and Catalytic Activity of Molybdenum(VI)-Pyrazolylpyridine Complexes in Olefin Epoxidation. Crystal Structures of Monomeric Dioxo, Dioxo-mu-oxo, and Oxodiperoxo Derivatives
authors Coelho, AC; Nolasco, M; Balula, SS; Antunes, MM; Pereira, CCL; Paz, FAA; Valente, AA; Pillinger, M; Ribeiro-Claro, P; Klinowski, J; Goncalves, IS
nationality International
journal INORGANIC CHEMISTRY
keywords BIDENTATE LEWIS-BASE; DIOXOMOLYBDENUM(VI) COMPLEXES; X-RAY; MOLYBDENUM(VI) DIOXO; MOLECULAR-STRUCTURE; TUNGSTEN COMPLEXES; TERT-BUTYL; LIGAND; REACTIVITY; PEROXO
abstract 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(mu(2)-O)Cl-2(PzPy)(2)] complexes, or the oxodiperoxomolybdenum(VI) complex [MoO(O-2)(2)Cl(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-H groups, weak CH center dot center dot center dot O and CH center dot center dot center dot pi contacts, and strong pi-pi stacking. Complexes 1 and 5 are moderately active catalysts for the epoxidation of cis-cyclooctene at 55 degrees 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(mu(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.
publisher AMER CHEMICAL SOC
issn 0020-1669
year published 2011
volume 50
issue 2
beginning page 525
ending page 538
digital object identifier (doi) 10.1021/ic101384p
web of science category Chemistry, Inorganic & Nuclear
subject category Chemistry
unique article identifier WOS:000285956600021

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