Formation of a Strong Heterogeneous Aluminum Lewis Acid on Silica. Issue 40 (31st August 2022)

• Record Type: Journal Article
• Authors: Samudrala, Kavyasripriya K.; Huynh, Winn; Dorn, Rick W.; Rossini, Aaron J.; Conley, Matthew P.
• Is Part Of: Angewandte Chemie international edition. Volume 61:Issue 40(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-08-31
• Subjects: Aluminum -- Fluoride Ion Affinity -- Heterogeneous Catalysis -- Lewis Acid -- Solid-State NMR; Chemistry -- Periodicals; 540
• DOI: 10.1002/anie.202205745
• Languages: English
• ISSNs: 1433-7851

Abstract

Abstract: Al(OC(CF3 )3 )(PhF) reacts with silanols present on partially dehydroxylated silica to form well‐defined ≡SiOAl(OC(CF3 )3 )2 (O(Si≡)2 ) (1 ). 27 Al NMR and DFT calculations with a small cluster model to approximate the silica surface show that the aluminum in 1 adopts a distorted trigonal bipyramidal coordination geometry by coordinating to a nearby siloxane bridge and a fluorine from the alkoxide. Fluoride ion affinity (FIA) calculations follow experimental trends and show that 1 is a stronger Lewis acid than B(C6 F5 )3 and Al(OC(CF3 )3 )(PhF) but is weaker than Al(OC(CF3 )3 ) and i Pr3 Si + . Cp2 Zr(CH3 )2 reacts with 1 to form [Cp2 ZrCH3 ][≡SiOAl(OC(CF3 )3 )2 (CH3 )] (3 ) by methide abstraction. This reactivity pattern is similar to reactions of organometallics with the proposed strong Lewis acid sites present on Al2 O3 . Abstract : Al(OC(CF3 )3 )3 (PhF) reacts with partially dehydroxylated silica to form very strong Lewis acid sites. The well‐defined aluminum Lewis acids are significantly stronger than common molecular Lewis acids and engage in alkyl abstraction reactions that are uncommon using well‐defined supported Lewis acids.