Crystal Structure and Catalytic Behavior in Olefin Epoxidation of a One-Dimensional Tungsten Oxide/Bipyridine Hybrid

Abstract

The tungsten oxide/2,2'-bipyridine hybrid material [WO3(2,2'-bpy)]·nH2O (n = 1-2) (1) has been prepared in near quantitative yield by the reaction of H2WO4, 2,2'-bpy, and H2O in the mole ratio of ca. 1:2:700 at 160 °C for 98 h in a rotating Teflon-lined digestion bomb. The solid-state structure of 1 was solved and refined through Rietveld analysis of high-resolution synchrotron X-ray diffraction data collected for the microcrystalline powder. The material, crystallizing in the orthorhombic space group Iba2, is composed of a one-dimensional organic-inorganic hybrid polymer, ∞(1)[WO3(2,2'-bpy)], topologically identical to that found in the previously reported anhydrous phases [MO3(2,2'-bpy)] (M = Mo, W). While in the latter the N,N'-chelated 2,2'-bpy ligands of adjacent corner-shared {MO4N2} octahedra are positioned on the same side of the 1D chain, in 1 the 2,2'-bpy ligands alternate above and below the chain. The catalytic behavior of compound 1 for the epoxidation of cis-cyclooctene was compared with that for several other tungsten- or molybdenum-based (pre)catalysts, including the hybrid polymer [MoO3(2,2'-bpy)]. While the latter exhibits superior performance when tert-butyl hydroperoxide (TBHP) is used as the oxidant, compound 1 is superior when aqueous hydrogen peroxide is used, allowing near-quantitative conversion of the olefin to the epoxide. With H2O2, compounds 1 and [MoO3(2,2'-bpy)] act as sources of soluble active species, namely, the oxodiperoxo complex [MO(O2)2(2,2'-bpy)], which is formed in situ. Compounds 1 and [WO(O2)2(2,2'-bpy)] (2) were further tested in the epoxidation of cyclododecene, trans-2-octene, 1-octene, (R)-limonene, and styrene. The structure of 2 was determined by single-crystal X-ray diffraction and found to be isotypical with the molybdenum analogue.

Metal oxide-triazole hybrids as heterogeneous or reaction-induced self-separating catalysts

“…3). By contrast, compound 2 exhibits a needle-like morphology, quite similar to that found recently for [WO 3 (2,2 0 -bipyridine)] [32]. The FT-IR spectra of 1 and 2 are similar in the range of 1000-3200 cm À1 , displaying bands that are attributed mainly to the triazole ligand (Fig.…”

“…The [46], oxodiperoxo complexes of the type [MO(O 2 ) 2 (L)] supported on mesoporous SBA-15 materials [47], and the hybrid materials [MO 3 (2,2 0 -bipy)]ÁnH 2 O (n = 0-2) [32]. As mentioned in the introduction, when aqueous H 2 O 2 is used as the oxidant, the latter materials are converted to the partially soluble oxodiperoxo complexes [MO(O 2 ) 2 (2,2 0 -bipy)], which are the active species responsible for the epoxidation reaction in homogeneous phase.…”

“…The material [MoO 3 (trz) 0.5 ] (trz = 1,2,4-triazole), which was first reported by Zubieta and co-workers [26], was chosen for study as part of our ongoing investigations into the catalytic properties of molybdenum(VI) and tungsten(VI) oxide-organonitrogen hybrid materials [27][28][29][30][31][32]. Depending on the structure and composition of these hybrids, as well as the catalytic reaction conditions, the materials typically act either as sources of soluble active species or (more http://dx.doi.org/10.1016/j.jcat.2016.06.005 0021-9517/Ó 2016 Elsevier Inc. All rights reserved.…”

“…rarely) as heterogeneous catalysts. For example, when the materials [Mo 2 O 6 (2-(1-pentyl-3-pyrazolyl)pyridine)] [30], [Mo 3 O 9 (2-[3(5)-pyrazolyl]pyridine)] [31] and [MO 3 (2,2 0 -bipy)] (M = Mo, W; 2,2 0 -bipy = 2,2 0 -bipyridine) [32] are used in catalytic olefin epoxidation with either tert-butylhydroperoxide (TBHP) or hydrogen peroxide as oxidant, they are irreversibly converted into soluble oxodiperoxo complexes of the type [MO(O 2 ) 2 (L)], which are responsible for the homogeneous catalytic reaction of the olefin. The efficient recovery and reuse of these complexes is not trivial, typically requiring precipitation with organic solvents.…”

Synthetic utility of metal catalyzed hydrogen peroxide oxidation of C-H, C-C and C=C bonds in alkanes, arenes and alkenes: Recent advances

“…161 The catalytic behavior in olefin epoxidation of a one-dimensional tungsten oxide/2,2'-bipyridine hybrid material was also recently reported. 162 Iron-catalyzed asymmetric epoxidation is attractive owing to the availability, low cost, and low toxicity of iron salts. Generally, the iron catalysts for asymmetric epoxidation can be classified into two categories: porphyrin-and non-porphyrin iron complexes.…”