Macrocyclic Dinuclear Palladium Complex as a Novel Doubly Threaded [3]Rotaxane Scaffold and Its Application as a Rotaxane Cross-Linker

A dinuclear Pd^II complex possessing a cyclic ligand was developed as a novel doubly threaded [3]rotaxane scaffold and applied as a rotaxane cross-linker reagent. The dinuclear complex (PdMC)₂ was prepared by one-step macrocyclization followed by the double palladation reaction. ¹ H NMR analysis and UV/Vis measurements revealed the formation of a doubly threaded pseudo[3]rotaxane by the complexation of (PdMC)₂ with 2 equivalents of 2,6-disubstituted pyridine 3 through double metal coordination. The treatment of (PdMC)₂ with 2 equivalents of 4-vinylpyridine (VP) afforded a doubly threaded [3]rotaxane cross-linker (PdMC-VP)₂ . Radical co-polymerization of VP and t-butylstyrene in the presence of (PdMC-VP)₂ afforded a stable rotaxane cross-linked polymer (RCP). An elastic RCP was also prepared by using n-butyl acrylate as a monomer. The obtained RCPs exhibited higher swelling ability and higher mechanical toughness compared with the corresponding covalent cross-linked polymers.