Characterization of a chiral menthyldimethyltin molybdate and its use as an olefin epoxidation catalyst
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Catalysis Letters, Vol. 114, Nos. 1–2, March 2007 ( 2007) DOI: 10.1007/s10562-007-9048-2
Characterization of a chiral menthyldimethyltin molybdate and its use as an olefin epoxidation catalyst Marta Abrantes,a Anabela A. Valente,b Martyn Pillinger,b Carlos C. Roma˜o,a and Isabel S. Gonc¸alves,b,* a
Instituto de Tecnologia Quı´mica e Biolo´gica da Universidade Nova de Lisboa, Av. da Republica, Estac¸a˜o Agrono´mica Nacional, 2780-157 Oeiras, Portugal b Department of Chemistry, CICECO, University of Aveiro, Campus de Santiago, 3810-193 Aveiro, Portugal
Received 22 November 2006; accepted 12 January 2007
Vibrational spectroscopy and EXAFS studies of an organotin molybdate with the formula [((Me)2(menthyl)Sn)2MoO4(H2O)3.5] reveal that the compound is polymeric and contains [MoO4]2) tetrahedra coordinated to [R3Sn]+ cationic spacers. The compound can be used as a recyclable solid catalyst for the selective epoxidation of cyclooctene by tert-butylhydroperoxide. In the epoxidation of prochiral olefins such as trans-b-methylstyrene, the corresponding epoxide isomers are obtained with fairly good to excellent selectivity, albeit with low enantiomeric or diastereomeric excesses. KEY WORDS: molybdenum; tin; (–)-menthyl; organic–inorganic hybrid composites; heterogeneous catalysis; olefin epoxidation.
1. Introduction Research on organic-inorganic hybrid materials with infinite (polymeric) structures has grown exponentially over the last 10 years or so [1–4]. One of the most appealing strategies is the formation of coordination networks through the aggregation via intermolecular bonds of two or more modular units. The self-assembly of organotin cationic fragments such as Me3Sn+ with different anionic metal-containing species has provided a large family of supramolecular organometallic networks with either 1-dimensional (1D), 2D or 3D architectures [5–23]. In 1993 Fischer and co-workers described a series of compounds with the general formula [(R3E)2MO4] (R = Me, Et, nPr, nBu, or Ph; E = Sn or Pb; M = Mo or W) [19]. The trimethyltin molybdate has a layered structure built up of MoO4 tetrahedra and Me3SnO2 trigonal-bipyramids which are linked by common oxygen atoms. This family was recently extended to include 1D coordination polymers of the type (NBu4)[(Me3Sn)MO4] (M = Mo, W) [21] and the 3D polymer (NBu4)[(Ph3Sn)3(MoO4)2] [20]. Although a large number of potential applications can be envisaged for these hybrid materials [3], particularly in the fields of optics, electronics, gas adsorption and catalysis, most of the published work has been restricted to synthesis and characterization. We have been studying polymeric organotin molybdates, tungstates and vanadates as catalysts for the liquid-phase oxidation of organic compounds [24–27]. The organotin molybdates [(R3Sn)2MoO4] (R = Me, *To whom correspondence should be addressed. E-mail: [email protected].
nBu, cyclohexyl, phenyl, benzyl) were tested as catalysts for the oxidation of benzothiophene and for the epoxidation of olefins, using either tert-butylhydroperoxide (tBuOOH)
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