Sunlight-Induced Covalent Marriage of Two Triply Interlocked Pd6 Cages and Their Facile Thermal Separation

A template-free triply interlocked Pd6 cage (2) was synthesized by two-component self-assembly of cis-blocked 90° acceptor cis-(tmen)­Pd­(NO3)2 (M) and 1,3,5-tris­((E)-2-(pyridin-3-yl)­vinyl)­benzene (L). Assembly 2 was characterized by 1H NMR and ESI-MS, and the structure was confirmed by X-ray crystallography, which revealed a parallel conformation of the olefin double bonds belonging to the adjacent cages in the solid state at a distance of 3.656 Å, thereby indicating the feasibility of [2+2] photochemical reaction. Two adjacent interlocked cages were covalently married together by intermolecular [2+2] cycloaddition in a single crystal-to-single crystal fashion upon exposure to sunlight/UV irradiation. Most surprisingly, the covalently married pair was easily separated thermally in aqueous medium under mild reaction conditions.