Encapsulation of Aromatic Molecules in Hexanuclear Arene Ruthenium Cages: A Strategy to Build Up Organometallic Carceplex Prisms with a Dangling Arm Standing Out

Self-assembly of 2,4,6-tris(pyridin-4-yl)-1,3,5-triazine (tpt)
subunits with p-cymene (p-PriC6H4Me) or hexamethylbenzene (C6Me6) 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 [Ru6(p-PriC6H4Me)6(tpt)2(dhbq)3]6+ ([1]6+), [Ru6(p-PriC6H4Me)6(tpt)2(dchq)3]6+ ([2]6+),
[Ru6(C6Me6)6(tpt)2(dhbq)3]6+ ([3]6+), and [Ru6(C6Me6)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 1H NMR experiments, mass spectrometry, and the single-crystal
structure analysis of [pyrene⊂1][O3SCF3]6 and [benzo[e]pyrene⊂1][O3SCF3]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 1H NMR experiments and ESI-MS.