Silica-supported metal acetylacetonate catalysts with a robust and flexible linker constructed by using 2-butoxy-3,4-dihydropyrans as dual anchoring reagents and ligand donors

Anchoring of a metal complex catalyst onto a solid support with a covalent bond has been widely used in designing a recyclable catalyst at molecular level. However, the performance of the obtained solid catalyst relies heavily on the stability and flexibility of the linker between the metal complex and the solid support. A ring-opening reaction of 2-butoxy-3,4-dihydropyrans with mercaptan was known to produce 2-alkylated 1,3-dicarbonyl compounds, which featured good atom economy, excellent yield and mild conditions. With the aid of this reaction, we used, in this work, 2-butoxy-3,4-dihydropyrans as dual anchoring reagents and ligand donors to modify a ready-made SH-functionalized HMS. This opened an easy way to construct a robust and flexible linker for anchoring a metal acetylacetonate complex catalyst onto the HMS support. The thereby obtained HMS can be used to immobilize Cu(acac)(2), Zn(acac)(2) and Ru(acac)(3) complexes. The obtained solid catalysts were fully characterized by many physicochemical methods. In the selected reactions, these catalysts not only displayed better or comparable activity in various organic reactions as compared with their homogeneous counterparts but also were proved to be quite robust and can be recycled several times without significant loss of their activities.