Discrete Rectangles, Prisms, and Heterometallic Cages from a Conjugated Cp*Rh-Based Building Block

By carefully selecting an existing synthetic strategy and suitable coordination subunits, constructing desired coordination geometries is no longer that difficult to accomplish. Herein, a new strategy to construct a series of unprecedented structures by using conjugated Cp*Rh-based complex BN-OTf (Cp*=eta(5)-C5Me5) as the building block is proposed. DFT calculations revealed extensive delocalized pi bonds in the subunit. With BN-OTf, rectangular macrocycles TN-bpy and TN-bpe were controllably synthesized. Single-crystal XRD studies confirmed one-dimensional stacking channels for the tetranuclear structure. Notably, the starting ligand imidazole-4,5-dicarboxylate was found to act not only as a tetradentate but also as a hexadentate ligand that can coordinate to further metal ions. Subsequently, [4Rh+1M] heterometallic complexes HMZ (M=Cu and Zn) were accessed by chelating borderline hard/soft Lewis acids. With TN-Linker or HMZ, two routes resulted in the [8Rh+2M] heterometallic cages HMC (M=Cu and Zn) with excellent crystallinity and stability. Surprisingly, when BN-OTf bonded to rhodium itself, triangular prisms TP-Linker were obtained with high solubility after being linked by bipyridine linkers. Both the X-ray structure and H-1 NMR spectrum confirmed the novel isomerization of the triangular structures. All of the compounds were obtained in high yields and were fully characterized by H-1 NMR spectroscopy, elemental analysis, IR spectroscopy, and in most cases single-crystal X-ray structure determination.