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

Abstract

The hybrid metal oxide-triazole materials [MoO3(trz)(0.5)] (1) and [W2O6(trz)] (2) (trz = 1,2,4-triazole) have been hydrothermally synthesized and characterized by different techniques (TGA, SEM, H-1 and C-13 MAS NMR, FT-IR spectroscopy, and structure determination by Rietveld analysis of high resolution synchrotron powder XRD data). Materials 1 and 2 display distinct behaviors when applied as catalysts for oxidation reactions with alcohol, aldehyde, olefin and sulfide substrates, and are more effective with hydrogen peroxide as the oxidant than with tert-butylhydroperoxide. The Mo-VI hybrid 1 transforms into soluble active species during cis-cyclooctene epoxidation with H2O2. When consumption of H2O2 reaches completion, spontaneous reassembly of the 2-dimensional molybdenum oxide network of 1 takes place and the hybrid precipitates as a microcrystalline solid that can be easily separated and recycled. Reaction induced self-separation behavior occurs with 1, H2O2 and other substrates such as methyl oleate and methylphenylsulfide. The W-VI hybrid 2 behaves differently, preserving its structural features throughout the heterogeneous catalytic process. (C) 2016 Elsevier Inc. All rights reserved.