Well-Defined Silica-Supported Mo–Alkylidene Catalyst Precursors Containing One OR Substituent: Methods of Preparation and Structure– Reactivity Relationship in Alkene Metathesis

摘要

The monosiloxy surface complexes [(SiO)MoACHTUNGTRENUNG(NAr)(=CHCMe2R’)( OR)] (R’=Me or Ph; OR= OtBu, OCMeACHTUNGTRENUNG(CF3)2 or OAr) are obtained by grafting onto SiO2(700) either symmetric Mo–alkylidene derivatives [MoACHTUNGTRENUNG(NAr)(=CHCMe2R’)(OR)2] or asymmetric derivatives, that is, with two different pendant ligands, one amido and one alkoxy/aryloxy, [MoACHTUNGTRENUNG(NAr)(=CHCMe2R’)(OR)ACHTUNGTRENUNG(NC6H8)]. The formation of these complexes was confirmed by mass-balance analysis,and infrared (IR) and NMR spectroscopies.These systems are highly efficient catalyst precursors for the metathesis of acyclic alkenes; the best results were seen when OR=OCMe- ACHTUNGTRENUNG(CF3)2. Nevertheless, they display poor performances in ring-closing metathesis, possibly due to the rigidity of the metal center (as evidenced by NMR spectroscopy), which therefore slows the rate of the metathesis.