In Quest of the Double Rotaxane Formation of the Bis(coronand) (1,5),(2,4)-Durenetetrayl-bis(18-crown-5) with Organomagnesium Compounds

The interaction between the title compound, bis(coronand) 8,and the diarylmagnesium compounds Ph2Mg and (p-tBuC6H4)2Mg in diethyl ether leads to the formation of 1:2 complexes (9 and 10, respectively), irrespective of the initial ratio of the components. In [D8]toluene, the three complex types can be discerned by 1H NMR spectroscopy: double side-on (9a, 10a), side-on/rotaxane (9b, 10b), and, to a very minor extent, double rotaxane (9c, 10c). In the case of 10a and 10b, the temperature dependence showed that rotaxane formation is enthalpically favored at the expense of a more negative entropy. As crystals suitable for structure determination could not be obtained from 9 and 10, the interaction of 8 with the sterically less demanding Hg(SCN)2 was studied. In this case, analogous pseudorotaxanes are formed exclusively, and both the 1:2 complex [8·{Hg(SCN)2}2] (11) and its 1:1 analogue 12 were observed. The double rotaxane structure of 11 was confirmed by X-ray crystal structure determination. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)