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.
keywords
BIDENTATE LEWIS-BASE; DIOXOMOLYBDENUM(VI) COMPLEXES; X-RAY; MOLYBDENUM(VI) DIOXO; MOLECULAR-STRUCTURE; TUNGSTEN COMPLEXES; TERT-BUTYL; LIGAND; REACTIVITY; PEROXO
subject category
Chemistry
authors
Coelho, AC; Nolasco, M; Balula, SS; Antunes, MM; Pereira, CCL; Paz, FAA; Valente, AA; Pillinger, M; Ribeiro-Claro, P; Klinowski, J; Goncalves, IS
our authors
Anabela Tavares Aguiar Valente
Principal Researcher
Filipe Alexandre Almeida Paz
Principal Researcher
Isabel Maria de Sousa Gonçalves
Associate Professor
Maria Margarida Feitor Pintão Moreno Antunes
Junior Researcher
Mariela Martins Nolasco
Assistant Researcher
Martyn Pillinger
Principal Researcher
Paulo Ribeiro-Claro
Associate Professor with AggregationGroups
G1 - Porous Materials and Nanosystems
G4 - Renewable Materials and Circular Economy
G6 - Virtual Materials and Artificial Intelligence
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 funding (Project PTDC/QUI/71198/2006). The FCT is acknowledged for a Ph.D. grant to A.C.C. and for the financial support towards the purchase of the Bruker APEX 11 single-crystal diffractometer.