Confinement of the Grubbs catalyst in alkene-functionalized mesoporous silica

• Impact of alkyl chain length of olefin moieties anchored into silica mesopores.
• Confinement behavior and stability of the first-generation Grubbs catalyst.
• Ordered mesoporous SBA-15 silica materials functionalized with alkenyl-trichlorosilanes.
• Characterization by solid state NMR and infra-red spectroscopies.
• Occurrence of ring-closing metathesis on the substrates.

Herein, we report on the impact of alkyl chain length of olefin moieties anchored into silica mesopores on the confinement behavior and stability of the first-generation Grubbs catalyst, i.e., [RuCl2(C(H)(Ph))(PCy3)2]. In this contribution, ordered mesoporous SBA-15 silica materials were functionalized with alkenyl-trichlorosilanes exhibiting different carbon chain lengths, e.g., vinyl- (C2), allyl- (C3), hexenyl- (C6) and octenyl- (C8) trichlorosilanes. Subsequently, the Grubbs I catalyst was incorporated into these different host materials in the presence of organic solvent. The thus-obtained materials, before and after interaction with Grubbs I, were characterized by a variety of methods, including N2 physisorption, thermogravimetric analyses, solid state NMR (13C, 31P and 29Si) and attenuated total reflectance (ATR) infra-red spectroscopy. Our investigations reveal a pronounced dependence of the Grubbs surface stability as a function of the grafted alkyl chain length of the alkene moieties. The nature of the immobilized Ru-based species is function of the surface modification and the presence of residual silanol groups.

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