Well-Defined Surface Species [( Si-O)W(=O)Me-3) Prepared by Direct Methylation of [( Si-O-)W(=O)Cl-3), a Catalyst for Cycloalkane Metathesis and Transformation of Ethylene to Propylene

The silica-supported tungsten oxo-trimethyl complex [( Si-O-)W(= O)Me-3] was synthesized using a novel SOMC synthetic approach. By grafting the inexpensive stable compound WOCl4 on the surface of silica, partially dehydroxylated at 700 degrees C (SiO2-700), a well-defined monopodal surface complex [( Si-O-)W(= O)Cl-3] was produced. The supported complex directly methylated with ZnMe2 and transformed into [( Si-O-)W(= O)Me-3], which we fully characterized by microanalysis, IR, mass balance and SS NMR (H-1, C-13, H-1-C-13 HETCOR, H-1-H-1 DQ and TQ). [( Si-O)W(= O)Me-3] 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 C-13 CP/MAS and H-1 spin echo MAS solid-state NMR; this was also confirmed by NMR and DFT calculations. [( Si-O)W(= O)Me-3] 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)Me-3] proved to be highly active for selective transformation of ethylene to propylene compared to other silica-supported organometallic complexes