Reinvestigation of Supramolecular Complexes with Cyclophanes of the Stetter and Koga Type: Agreement and Disagreement with Solid-State Structures

In this paper we reinvestigate the historically oldest complexations with cyclophanes of the Stetter and Koga type (1 and 2), and new macrocycle 3, which is a hybrid of the two former. NMR titrations in aqueous solution reveal that benzene forms, as known, strong complexes with Koga-type host 2, but also weaker ones with Stetter cyclophane 1, in contrast to earlier observations with the corresponding crystals. Tosylate forms weak complexes with 1, but stronger ones with 2 and 3. The binding free energy difference (Delta G = 7 kJ mol(-1)) between tosylate and benzene as guest and 2 or 3 as host agrees well with the salt bridge increment found earlier with many supramolecular complexes. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)