ic5b00928_si_001.cif (20.95 kB)
Download fileCrystal Structure and Catalytic Behavior in Olefin Epoxidation of a One-Dimensional Tungsten Oxide/Bipyridine Hybrid
dataset
posted on 2015-10-19, 00:00 authored by Tatiana R. Amarante, Margarida
M. Antunes, Anabela A. Valente, Filipe A. Almeida Paz, Martyn Pillinger, Isabel S. GonçalvesThe 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.