The Role of L-Ligands in Silica-Supported Ti Oxo/Imido Heterometathesis Catalysts

We report here the preparation and characterization of new well-defined silica-supported Ti imido complexes that present an L-ligand variation in a structure of currently the most active oxo/imido heterometathesis catalyst (equivalent to SiO)Ti(=NtBu)(Me2Pyr)(py)2 (1s), where py is replaced with stronger electron-donating 4-(N,N-dimethylamino)pyridine (2s) or bidentate 2,2 '-bipyridine (3s). The materials were characterized with elemental and mass balance analyses and IR and solid-state NMR that confirmed the selective formation of surface Ti species with terminal imido ligand. Evaluation of the catalytic oxo/imido heterometathesis activity of the obtained materials demonstrated that L-ligands have a pronounced influence on the catalytic performance. In particular, the replacement of pyridine with stronger donating ligands resulted in a significant drop of activity. The catalytic results are discussed in view of the reaction mechanism and implications for further catalyst development. Variation of L-ligands in well-defined silica-supported Ti imido complexes gives mechanistic insight into catalytic oxo/imido heterometathesis reactions and provides implications for further catalyst development.image