Photoreversible [2] Catenane via the Host-Guest Interactions between a Palladium Metallacycle and β-Cyclodextrin

We report the efficient preparation of an A2D2 (A = acceptor and D = donor) metallacycle 2 = [(en)2Pd2(1)2](NO3)4, using the coordination driven self-assembly of trans-azobenzene based bispyridyl ligand 1 and (en)Pd(NO3)2 (en = ethylenediamine). In the metallacycle, the trans-azobenzene units serve both as a structural element and as sites for subsequent host–guest chemistry with β-cyclodextrin, leading to the formation of a [2] catenane 3. This catenation process is reversible and can be switched off and on in a photocontrollable manner via the trans–cis isomerization of the azobenzene units.