Encapsulation of Aromatic Molecules in Hexanuclear Arene Ruthenium Cages: A Strategy to Build Up Organometallic Carceplex Prisms with a Dangling Arm Standing Out Johan Mattsson, † Padavattan Govindaswamy, † Julien Furrer, † Yoshihisa Sei, ‡ Kentaro Yamaguchi, ‡ Georg Su ¨ss-Fink, † and Bruno Therrien* ,† Institut de Chimie, UniVersite ´ de Neucha ˆtel, Case postale 158, CH-2009 Neucha ˆtel, Switzerland, and Faculty of Pharmaceutical Sciences at Kagawa Campus Tokushima Bunri UniVersity, Shido, Sanuki-city, Kagawa 769-2193, Japan ReceiVed May 9, 2008 Self-assembly of 2,4,6-tris(pyridin-4-yl)-1,3,5-triazine (tpt) subunits with p-cymene (p-Pr i C 6 H 4 Me) or hexamethylbenzene (C 6 Me 6 ) ruthenium building blocks and 2,5-dihydroxy-1,4-benzoquinonato (dhbq) or 2,5-dihchloro-3,6-dihydroxy-1,4-benzoquinonato (dchq) bridges affords the triangular prismatic organometallic cations [Ru 6 (p-Pr i C 6 H 4 Me) 6 (tpt) 2 (dhbq) 3 ] 6+ ([1] 6+ ), [Ru 6 (p-Pr i C 6 H 4 Me) 6 (tpt) 2 (dchq) 3 ] 6+ ([2] 6+ ), [Ru 6 (C 6 Me 6 ) 6 (tpt) 2 (dhbq) 3 ] 6+ ([3] 6+ ), and [Ru 6 (C 6 Me 6 ) 6 (tpt) 2 (dchq) 3 ] 6+ ([4] 6+ ). These hexanuclear cationic cages are isolated in good yield as their triflate salts. The assembly of 1-4 can also be achieved in the presence of large aromatic molecules such as pyrene, fluoranthene, benzo[e]pyrene, triphenylene, or coronene to give the corresponding inclusion systems [aromatic⊂1] 6+ , [aromatic⊂2] 6+ , [aromatic⊂3] 6+ , and [aromatic⊂4] 6+ . The closed proximity of the encapsulated molecule with the different components of the cage and the carceplex nature of these systems are confirmed by one-dimensional ROESY 1 H NMR experiments, mass spectrometry, and the single-crystal structure analysis of [pyrene⊂1][O 3 SCF 3 ] 6 and [benzo[e]pyrene⊂1][O 3 SCF 3 ] 6 . Pyrene can be encapsulated even if it contains a functionalized aliphatic substituent; in this case the aromatic moiety is included in the cage, while the functionalized side arm stands out. Thus, methyl 4-(pyren-1-yl)butanoate (pyrene-R) is encapsulated in 1 to give the carceplex [pyrene-R⊂1] 6+ , in which the methyl butyrate arm dangles outside the cage while the pyrene moiety is firmly trapped by the metallo-prismatic cation, as demonstrated by 1 H NMR experiments and ESI-MS. Introduction Self-assembly is a process leading to the formation of discrete nanometer-sized objects or well-defined aggregates in which the overall structure is controlled by the symmetry of the different building blocks. 1 In the case of metallo-supramolecular assemblies, the coordination mode of the metal center as well as the symmetry of the ligands needs to be controlled in order to allow the formation of the desired aggregates. 2 The square- planar geometries of platinum(II) and palladium(II) have been extensively exploited to generate supramolecular assemblies. 3 However, a variety of other metals with octahedral geometries have also been used for the self-assembly of supramolecular complexes. 4 Encapsulation of guest molecules in this type of metallo-supramolecular assemblies is of great interest and the subject of many studies. 5 These molecular capsules have many potential applications, ranging from drug delivery systems to molecular reaction chambers for catalysis and stabilization of reactive intermediates. 6 Recently, we synthesized a cationic triangular metallo-prism, [Ru 6 (p-Pr i C 6 H 4 Me) 6 (tpt) 2 (dhbq) 3 ] 6+ ([1] 6+ ), which allowed the encapsulation of square-planar complexes M(acac) 2 [M ) Pd, Pt; acac ) acetylacetato] 7 and triphenylene derivatives. 8 The cytotoxic activities of the “complex-in-a-complex” derivatives [(acac) 2 M⊂1] 6+ were evaluated in comparison with free M(acac) 2 and showed that, like a “Trojan horse”, once inside a cell, leaching of the guest from the cage accelerates and increases the cytotoxic effect. 7 Permanent encapsulation of a large aromatic guest such as hexahydroxytriphenylene [C 18 H 6 (OH) 6 ] and hexamethoxytriphenylene [C 18 H 6 (OMe) 6 ] was * Corresponding author. 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