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

Cationic tetranuclear arene ruthenium complexes of the general formula [Ru 4 ( 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) 2 Cl 2 ] (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 AgCF 3 SO 3 . 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 [D 3 ]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 [D 3 ]acetonitrile. DOSY measurements suggest that, in the case of [Ru 4 ( 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‐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.