Well-defined silica-supported Mo-alkylidene catalyst precursors containing one OR substituent: Methods of preparation and structure-reactivity relationship in alkene metathesis

Abstract

The monosiloxy surface complexes [(≡SiO)Mo(≡NAr)(=CHC-Me 2R′)(OR)± (R′ = Me or Ph; OR = OtBu, OCMe(CF 3)2 or OAr) are obtained by grafting onto SiO 2-(700) either symmetric Mo-alkylidene derivatives [Mo(≡NAr)(=CHCMe2R′)(OR)2± or asymmetric derivatives, that is, with two different pendant ligands, one amido and one alkoxy/aryloxy, [Mo(≡ NAr)(=CHCMe2R′)(OR)(NC 6H8)±. 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-(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. © 2009 Wiley-VCH Verlag GmbH & Co. KGaA.