Designing the host-guest properties of tetranuclear arene ruthenium metalla-rectangles to accommodate a pyrene molecule

Abstract

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 [Ru 2(p-cymene)2(dhnq)2Cl2] (dhnq = 5,8-dihydroxy-l,4-naphthoquinonato) with pyrazine or bipyridine linkers [N∩N = pyrazine, 1; 4,4'-bipyridme, 2; l,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 (ID, DOSY, ROESY). In [D 3]acetonitrile, the pyrazine-containing metalla-rectangle 1 shows no meaningful interactions with pyrene. On the other hand, the 4,4'-bipyridine- and l,2-bis(4-pyridy1)ethylenecontaining 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 [Ru 4(p-cymene) 4{1,2-bis(4-pyridy1)ethylene} 2(dhnq)2]4+ (3), the pyrene molecule is found inside the hydrophobic cavity of the metallarectangle, thus giving rise to a host-guest system. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA.