In- and out-of-cavity interactions by modulating the size of ruthenium metallarectangles

Abstract

Cationic (arene)ruthenium-based tetranuclear complexes of the general formula [Ru4(η6-pcymene) 4(μ-N∩N) 2(μ-OO∩OO)2]4+ were obtained from the dinuclear (arene)ruthenium complexes [Ru2(η6-p-cymene) 2(μ-OO∩OO)2Cl2] (p-cymene=1-methyl-4-(1- methylethyl)benzene, OO∩OO=5,8-dihydroxy-1,4-naphthoquinonato (2-), 9,10-dihydroxy-1,4-anthraquinonato(2-), or 6,11-dihydroxynaphthacene-5,12- dionato(2-)) by reaction with pyrazine or bipyridine linkers (N∩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 CF 3SO3- 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. © 2010 Verlag Helvetica Chimica Acta AG.