Highly Selective Construction of Unique Cyclic [4]catenanes ( 841 ) Induced by Multiple Noncovalent Interactions

The synthesis of high-ordered mechanically interlocked supramolecular structures is an extremely challenging topic. Only two linear [4]catenanes have been reported so far and there is no defined strategy to obtain cyclic [4]catenane. Herein, two unprecedented cyclic [4]catenanes, 1 and 2, were prepared in high yields. The syntheses rely on the strategic selection of naphthalenediimide (NDI) based Cp*Rh/Ir building blocks E1/E2 (Cp* = pentamethyl-cyclopentadienyl) and nonlinear diimidazole ligand precursor L1, exhibiting large conjugate plane, appropriate coordination angles, and freely rotating imidazole units, thereby enabling multiple π···π stacking interactions to maintain the supramolecular structures. The use of other Cp*Rh building blocks E3, E4 or E5 featuring slightly shorter metal-to-metal distances than E1/E2 and different chemical properties led to the formation of a complex 3 and two metallamacrocycles 4 or 5, respectively. The structures of these assemblies were confirmed by X-ray crystallographic analysis, ESI-TOF-MS and NMR spectroscopy. Complex 1, exhibiting a broad-band absorption in the UV/Vis to NIR regions and a remarkable photothermal conversion was thereafter used to build the new 1 membrane. The solar power-induced water steam generation performance of 1 membrane was investigated, reaching a value of 2.37 kg·m-2·h-1, making it suitable for collection of fresh water via desalination and wastewater.