Highly active, water-compatible and easily separable magnetic mesoporous Lewis acid catalyst for the Mukaiyama–Aldol reaction in water
A novel magnetic mesoporous Lewis acid catalyst was prepared through immobilizing Yb(OTf)3 on a sodium propylsulphonate and phenyl group co-functionalized magnetic core–mesoporous silica shell composite. The obtained Yb(OTf)2-SO3Na&Ph-MCMSS catalyst had a typical core–shell structure with a Fe3O4 magnetic core, a middle amorphous silica layer and a multifunctional mesoporous silica shell with radial pore channels. In water medium Mukaiyama–Aldol reactions, it exhibited a higher catalytic reactivity than that of the homogeneous catalyst Yb(OTf)3, and control catalysts Yb(OTf)2-SO3Na-MCMSS without phenyl groups inside the mesoporous channels, Yb(OTf)2-SO3Na&Ph-MCSS without a mesoporous structure, mesoporous Yb(OTf)2-SO3Na&Ph-MCM-41 with an irregular morphology and nonporous Yb(OTf)2-SO3Na-Amberlyst-15 ion-exchange resin. The systematic analysis demonstrated that this excellent catalytic performance could be attributed to the synergetic effect resulting from its radial mesoporous channels and the pore surface hydrophobicity, leading to the increased accessibility of actives sites and the decreased diffusion limitation of reactants. More importantly, this catalyst was stable in water and could be easily separated with a simple magnet and reused at least six times without loss of catalytic activity.