Crystalline Hybrid Solid Materials of Palladium and Decamethylcucurbit[5]uril as Recoverable Precatalysts for Heck Cross-Coupling Reactions

A series of MPdMe10CB[5] (M=Li, Na, K, Rb, and Cs; Me10CB[5]=decamethylcucurbit[5]uril) hybrid solid materials have been successfully synthesized for the first time through a simple diffusion method. These as-prepared hybrid solids have been applied as phosphine-free precatalysts for Heck cross-coupling reactions with excellent catalytic performance and good recyclability. In the processes of the catalytic reactions, the activated Pd-II species were released from the crystalline hybrid precatalysts and transformed into catalytically active Pd nanoparticles, which have been demonstrated as key to carry on the catalytic reactions for the recoverable precatalysts MPdMe10CB[5] (M=K, Rb, and Cs). It has also been rationalized that the introduction of different alkali metals afforded crystalline hybrid precatalysts with different crystal structures, which are responsible for their diversified stability and reusability presented in Heck reactions.