Supramolecular Catalysts by Encapsulating Palladium Complexes within Dendrimers

摘要

Dendrimers are of great interest as new materials for applications in many areas such as catalysts. A characteristic feature of dendrimers is the presence of internal cavities, which can host organic molecules and metal nanoparticles. Using this property, the catalytic active species can be introduced in the interior spaces of dendrimers to construct nanoreactors, which have received considerable attention because of their unique catalysis. Recently, we have reported on the substrate-specific hydrogenation of olefins based on the hydrogen bonds between the tertiary amino groups inside a poly(propylene imine) (PPI) dendrimer and substrates. This success has provided us with a new strategy for the design of dendrimer-encapsulated metal catalysts that utilize the inner nanoenvironment of the dendrimers. In this communication, we describe the novel immobilization of a Pd complex catalyst within the cavity of dendrimers through ionic bonds. The dendrimers encapsulating Pd complexes act as unique nanoreactors for Heck reactions and allylic aminations. Moreover, the dendritic nanoreactor could readily recovered using thermomorphic system. To date, there are only a few examples of the positive dendritic effects on the activity of catalysts, in which the active sites are incorporated inside the dendrimers.