Well-Defined Surface Species [(≡Si - O -)W(=O)Me₃] Prepared by Direct Methylation of [(≡Si - O -)W(=O)Cl₃], a Catalyst for Cycloalkane Metathesis and Transformation of Ethylene to Propylene

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 (SiO_2-700), 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. (Chemical Equation Presented).