SOMC-Designed Silica Supported Tungsten Oxo Imidazolin-2-iminato Methyl Precatalyst for Olefin Metathesis Reactions

Synthesis, structure, and olefin metathesis activity of a surface complex [(≡Si-O-)W(═O)(CH₃)₂-Im^DippN] (4) (Im^Dipp = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-iminato) supported on silica by a surface organometallic chemistry (SOMC) approach are reported. The reaction of N-silylated 2-iminoimidazoline with tungsten(VI) oxytetrachloride generated the tungsten oxo imidazolin-2-iminato chloride complex [Im^DippNW(═O)Cl₃] (2). This was grafted on partially dehydroxylated silica pretreated at 700 °C (SiO_2-700) to afford a well-defined monopodal surface complex [(≡Si-O-)W(═O)Cl₂-Im^DippN] (3). 3 underwent alkylation by ZnMe₂ to produce [(≡Si-O-)W(═O)(CH₃)₂-Im^DippN] (4). The alkylated surface complex was thoroughly characterized by solid-state NMR, elemental microanalysis, Raman, FT-IR spectroscopies, and XAS analysis. 4 proved to be an active precatalyst for self-metathesis of terminal olefins such as propylene and 1-hexene.