Designing the Host-Guest Properties of Tetranuclear Arene Ruthenium Metalla-Rectangles to Accommodate a Pyrene Molecule

• Published in: European Journal of Inorganic Chemistry 2010-02, Vol.2010 (5), p.725-728
• Main Authors: Barry, Nicolas P. E., Furrer, Julien, Freudenreich, Julien, Süss-Fink, Georg, Therrien, Bruno
• Format: Article
• Language: English
• Subjects: Arene ligands; Host-guest systems; Ruthenium­ complexes; Supramolecular chemistry
• ISSN: 1434-1948; 1099-0682
• DOI: 10.1002/ejic.200901026

Cationic tetranuclear arene ruthenium complexes of the general formula [Ru4(p‐cymene)4(N∩N)2(dhnq)2]4+ comprising rectangular structures are obtained in methanol from the reaction of the dinuclear arene ruthenium precursor [Ru2(p‐cymene)2(dhnq)2Cl2] (dhnq = 5,8‐dihydroxy‐1,4‐naphthoquinonato) with pyrazine or bipyridine linkers [N∩N = pyrazine, 1; 4,4′‐bipyridine, 2; 1,2‐bis(4‐pyridyl)ethylene, 3] in the presence of AgCF3SO3. All complexes 1–3, isolated in good yield as triflate salts, have been characterised by NMR and IR spectroscopy. The interaction of these rectangular complexes with pyrene as a guest molecule has been studied in solution by various NMR techniques (1D, DOSY, ROESY). In [D3]acetonitrile, the pyrazine‐containing metalla‐rectangle 1 shows no meaningful interactions with pyrene. On the other hand, the 4,4′‐bipyridine‐ and 1,2‐bis(4‐pyridyl)ethylene‐containing metalla‐rectangles 2 and 3 clearly interact with pyrene in [D3]acetonitrile. DOSY measurements suggest that, in the case of [Ru4(p‐cymene)4(4,4′‐bipyridine)2(dhnq)2]4+ (2), the interactions occur on the outside of the rectangular assembly, while in the case of [Ru4(p‐cymene)4{1,2‐bis(4‐pyridyl)ethylene}2(dhnq)2]4+ (3), the pyrene molecule is found inside the hydrophobic cavity of the metalla‐rectangle, thus giving rise to a host‐guest system. A series of cationic tetranuclear arene ruthenium complexes connected with pyrazine, 4,4′‐bipyridine or 1,2‐bis(4‐pyridyl)ethylene N∩N linkers interact differently with pyrene in solution. While pyrene doesnot interact with the pyrazine‐containing metalla‐rectangle, it interacts with the 4,4′‐bipyridine‐containing metalla‐rectangle and goes into the cavity of the 1,2‐bis(4‐pyridyl)ethylene system.