Multicavity [PdnL4]2n+ Cages with Controlled Segregated Binding of Different Guests

Abstract

Multicavity [Pdn(L)4]2n+ metallosupramolecular cages based on long backboned ligands are an attractive approach to increasing molecular size without loss of the binding specificity conferred by small cavity [Pd2(L)4]4+ assemblies. We herein report the synthesis of two double cavity polypyridyl [Pd3(L)4]6+ cages that bind cisplatin [Pt(NH3)2Cl2] within their internal cavities and interact with triflate (TfO-) on their exohedral faces. We also report the first example of a triple cavity [Pd4(L)4]8+ cage. This cage differs in that the central cavity is phenyl-linked rather than having the pyridyl core as in the peripheral cavities. The difference in cavity character results in selective guest binding of cisplatin in the peripheral cavities, with triflate binding within the central cavity and on the exohedral faces of the peripheral palladium(II) ions. All the cavities could be simultaneously filled by introducing both cisplatin and triflate concurrently, providing the first example of a discrete metallosupramolecular architecture with segregated guest binding in different designed internal cavities. The ligands and cages were characterized by NMR spectroscopy, mass spectrometry, elemental analysis, and, in one case, X-ray crystallography.