Investigation of Surface Alkylation Strategy in SOMC: In Situ Generation of a Silica-Supported Tungsten Methyl Catalyst for Cyclooctane Metathesis

An efficient and potentially scalable method is described for the synthesis of the silica-supported complexes [(equivalent to Si-O)WMe5] and [(equivalent to:Si-O)WMe2(equivalent to CH)] obtained by in situ alkylation of the surface-grafted tungsten chloride [(equivalent to Si-O)WCl5] (1). [(equivalent to Si-O)WCl5] can be readily prepared by the reaction of commercially available and stable tungsten hexachloride WCI6 with partially dehydroxylated silica at 700 degrees C (SiO2-700). Further reaction with ZnMe2 at room temperature rapidly forms a mixture of surfacealkylated tungsten complexes. They were fully characterized by microanalysis, FTIR, mass balance, and solid-state NMR (H-1, C-13, H-1-C-13 HETCOR, H-1-H-1 double quantum and triple quantum) and identified as [(equivalent to Si-O)WMes] and another product, [(equivalent to Si-O)WMe2(equivalent to CH)]. The latter might have been generated by partial decomposition of the tungsten methyl chloride compound, which is formed during the stepwise alkylation of [(equivalent to Si-O)WCl3]. DFT calculations were carried out to check the relative stability of the tungsten methyl chloride intermediates and the feasibility of the reaction and corroborate the experimental results. This tungsten complex and its derivative were found to be active catalysts for the metathesis of cydooctane.