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 Ph 2 Mg and ( p ‐ t BuC 6 H 4 ) 2 Mg in diethyl ether leads to the formation of 1:2 complexes ( 9 and 10 , respectively), irrespective of the initial ratio of the components. In [D 8 ]toluene, the three complex types can be discerned by 1 H 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)