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 ( η 6 ‐p ‐cymene) 4 ( μ‐N ∩ N ) 2 ( μ‐OO∩OO ) 2 ] 4+ were obtained from the dinuclear (arene)ruthenium complexes [Ru 2 ( η 6 ‐ p ‐cymene) 2 ( μ‐OO∩OO ) 2 Cl 2 ] ( 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′‐[(1 E )‐ethene‐1,2‐diyl]bis[pyridine]) in the presence of silver trifluoromethanesulfonate (CF 3 SO 3 Ag) ( Scheme ). All complexes 4 – 12 were isolated in good yield as CF 3 SO $\rm{{_{3}^{-}}}$ salts, and characterized by NMR and IR spectroscopy. The host–guest properties of the metallarectangles incorporating 4,4′‐bipyridine and (4,4′‐[(1 E )‐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′‐[(1 E )‐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.