In- and Out-of-Cavity Interactions by Modulating the Size of Ruthenium Metallarectangles

Cationic (arene)ruthenium-based tetranuclear complexes of the general formula [Ru-4(eta(6)-p-cymene)(4)(mu-N boolean AND N)(2)(mu-OO boolean AND OO)(2)](4+) were obtained from the dinuclear (arene)ruthenium complexes [Ru-2(eta(6)-p-cymene)(2)(mu-OO boolean AND OO)(2)Cl-2] (p-cymene =1-methy1-4-(1-methylethyl)benzene, OO boolean AND OO = 5,8-dihydroxy-1.4-naphthoquinonato(2-), 9,10-dihydroxy-1,4-anthraquinonato(2-). or 6,11-ciihydroxy-naphthacene-5,12-dionato(2-)) by reaction with pyrazine or bipyridine linkers (N boolean AND N = pyrazine, 4.4'-bipyridine, 4,4'-[(1E)-ethene-1,2-diyl]bis[pyridine]) in the presence of silver trifluoromethanesulfonate (CF3SO3Ag) (Scheme). All complexes 4-12 were isolated in good yield as CF3SO3 salts, and characterized by NMR and IR spectroscopy. The host - guest properties of the metallarectangles incorporating 4,4'-bipyridine and (4,4'-[(1E)-ethene-1,2-diyl]bis[pyridine] linkers were studied in solution by means of multiple NMR experiments (1D. ROESY, and DOSY). The largest metallarectangles 10-12 incorporating (4,4'-[(1E)-ethene-1,2-diyl]bis[pyridine] linkers are able to host an anthracene, pyrene, perylene, or coronene molecule in their cavity, while the medium-size metallarectangles 7-9 incorporating 4,4'-bipyridine linkers are only able to encapsulate anthracene. However, out-of-cavity interactions are observed between these 4,4'-bipyridine-containing rectangles and pyrene, perylene, or coronene. In contrast, the small pyrazine-containing metallarectangles 4-6 show no interaction in solution with this series of planar aromatic molecules.