The Assembly of Cerium(III)-Containing Silicotungstate with Lewis Acid–Base Sites Enables the Selective <i>C3</i>-Alkenylation of Oxindole
Zhou-Fu Lin, Guo‐Ping Yang, Wenjun Jiang, Jin-Cao Chen, Yufeng Liu
Abstract
A cerium(III)-containing silicotungstate, [H 2 N(CH 3 ) 2 ] 10 NaK[KCe(SiW 11 O 39 ) 2 (H 2 O)]·18.5H 2 O ( CeSiW ), was successfully synthesized and characterized. Structure analysis reveals that CeSiW is composed of two {SiW 11 O 39 } units connected by one cerium(III) cation to form a typical 1:2 sandwich structure, which is further expanding into a 1D chain linked by K + ions. The oxygen-enriched surfaces of {SiW 11 O 39 } units and open cerium sites provide abundant Lewis base and acid sites in CeSiW . As a result, CeSiW efficiently catalyzed the C3 -alkenylation of oxindoles with aldehydes through the simultaneous activation of both reaction substrates on its crystal framework. Various 3-benzylidene-oxindoles are synthesized with excellent yields and high E -selectivity under solvent-free conditions.