A. Hamieh, Y. Chen, S. Abdel-Azeim, E. Abou-hamad, S. Goh, M. Samantaray, R. Dey, L. Cavallo, J.M. Basset
ACS Catal., 5 (4), 2164-2171, (2015)
Surface organometallic chemistry, Tungsten oxo compound, Surface methylation, Cyclooctane metathesis, Ethylene propylene conversion
The silica-supported tungsten oxo-trimethyl complex [(≡Si—O—)W(═O)Me3] was synthesized using a novel SOMC synthetic approach. By grafting the inexpensive stable compound WOCl4 on the surface of silica, partially dehydroxylated at 700 °C (SiO2-700), a well-defined monopodal surface complex [(≡Si—O—)W(═O)Cl3] was produced. The supported complex directly methylated with ZnMe2 and transformed into [(≡Si—O—)W(═O)Me3], which we fully characterized by microanalysis, IR, mass balance and SS NMR (1H, 13C, 1H–13C HETCOR, 1H–1H DQ and TQ). [(≡Si—O)W(═O)Me3] has two conformational isomers on the surface at room temperature. The conversion of one to the other was observed at 318 K by variable-temperature 13C CP/MAS and 1H spin echo MAS solid-state NMR; this was also confirmed by NMR and DFT calculations. [(≡Si—O)W(═O)Me3] was found to be active in cyclooctane metathesis and to have a wide distribution range in ring-contracted and ring-expanded products. In addition, [(≡Si—O)W(═O)Me3] proved to be highly active for selective transformation of ethylene to propylene compared to other silica-supported organometallic complexes.