abstract
A solution obtained by dissolving MoO3 in aqueous hydrogen peroxide reacts with 4,4'-bipyridine (4,4'-bipy) to give the dinuclear oxodiperoxo complex [{MoO(O-2)(2)(4,4'-Hbipy)}(2)(mu-O)] (1). The unique structural feature of 1 with respect to other related complexes is the completion of the coordination sphere of the Mo atoms by a monoprotonated [4,4'-Hbipy](+) molecule, which is bound to the metal center through the unprotonated pyridine ring. The catalytic performance of 1 has been investigated for the epoxidation of the benchmark substrate cis-cyclooctene and three representative bio-olefins, namely limonene, methyl oleate and methyl linoleate, using either aq. H2O2 or tert-butylhydroperoxide (TBHP) oxidants. For the epoxidation of cis-cyclooctene, catalytic activity at 55 degrees C with TBHP was comparable with that at 70 degrees C with H2O2 (90-95% conversion at 24 h; turnover number in the range 90-95 mol(Cy) molMo(-1); 100% selectivity towards cyclooctene epoxide). The catalytic reactions are homogeneously catalysed and compounds were isolated from the reaction mixtures in order to ascertain the nature of the active species present in solution. With H2O2 as oxidant, the liquid-phase conversion of 1 to beta-octamolybdate anions, beta-[Mo8O26](4-), takes place during the 24 h catalytic batch run. The same transformation occurs when the molybdenum oxide-bipyridine hybrid compound [MoO3(4,4'-bipy)(0.5)] (2) is used as the (pre) catalyst instead of 1. With TBHP as oxidant, no species other than 1 were isolated from the recovered reaction solution. For the reactions with the bio-olefins (1, TBHP, 70 degrees C, 24 h), fairly high conversions of 68-92% were reached, with very high selectivity towards epoxide products (90-100%). Monoepoxides were the major products formed from limonene and methyl linoleate. (C) 2017 Elsevier B.V. All rights reserved.
keywords
HYDROGEN-PEROXIDE; CRYSTAL-STRUCTURES; LIMONENE OXIDE; MOLYBDENUM(VI) COMPLEXES; METHYL LINOLEATE; HIGHLY EFFICIENT; IONIC LIQUIDS; OXIDATION; PEROXOTUNGSTATE; OCTAMOLYBDATE
subject category
Chemistry
authors
Neves, P; Gomes, AC; Paz, FAA; Valente, AA; Goncalves, IS; Pillinger, M
our authors
Ana Catarina Costa Gomes Alves
Assistant Researcher
Anabela Tavares Aguiar Valente
Principal Researcher
Filipe Alexandre Almeida Paz
Principal Researcher
Isabel Maria de Sousa Gonçalves
Associate Professor
Martyn Pillinger
Principal Researcher
Patrícia dos Santos Neves
Assistant Researcheracknowledgements
This work was developed in the scope of the project CICECO-Aveiro Institute of Materials, POCI-01-0145-FEDER-007679 [FCT (Fundacao para a Ciencia e a Tecnologia) ref. UID/CTM/50011/2013], financed by national funds through the FCT/MEC and when applicable co-financed by FEDER (Fundo Europeu de Desenvolvimento Regional) under the PT2020 Partnership Agreement. The FCT and the European Union are acknowledged for post-doctoral grants to P.N. (SFRH/BPD/110530/2015) and A.C.G. (SFRH/BPD/108541/2015) co-funded by MCTES and the European Social Fund through the program POPH of QREN.