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

Abstract

AbstractCationic 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.