Formation of supramolecular adducts of ferrocene (guest) and cyclic head-to-tail trimers (hosts) derived from bile acid: 3a-hydroxy-5~-cholan-24-oic acid triolide ( l ) , 3a-hydroxy-7-oxo-5P-cholan-24-oic acid triolide (2), 3a-hydroxy-12-oxo-SPcholan-24-oic acid triolide (3), 3a-hydroxy-?a-trifluoroacetoxy-6P-cholan-24-oic acid triolide (4) and 3a-hydroxy-12a-TFA-5P-cholan-24-oic acid triolide (5) (TFA = trifluoroacetoxy) have been studied by 'H NMR. The best computer-assisted data fitting on the 'H-NMR chemical shift data was given by a 1:2 (guest/host) association model. The association constants vary in the range 170-990 M-', 7-0x0-substituted triolide 2 and 12a-TFA triolide 5 showing the largest and smallest values respectively. Generally, triolides bearing substituents at the position C-7 (2 and 4), when compared with the 12-substituted derivatives 3 and 5, seem to favour adduct formation, while a TFA group at the position C-7 or C-12 seems to hinder the adduct formation in comparison with the 0x0-substituted congeneers. This finding may be accounted for by the bulky character of the TFA group when compared to the 0x0 group.Cholaphanes and cyclocholates are cholic acid (3a,7a, 12a-trihydroxy-5~-cholan-24-oic acid) based macrolides capable of binding other biologically interesting molecules [']. Cholic acid macrolides have been mentioned as a structural fragment of a molecular bowl capable of selective binding of morphineL2]. Generally, bile acids have a rigid steroidal skeleton with curved profile which facilitates the design of macrolide frameworks"1. Furthermore, bile acids are of low cost, easily available, and occur in nature as pure enantiomers. These properties are of great importance in, for example, the design of asymmetric synthesis and catalysis as aided by these macrocyclic hosts.In our previous paper, we reported a 'H-NMR investigation into the interaction of anisole with five different bile acid based macrolides [3]. The unsubstituted macrolides (from cyclic lithocholate diolide to pentolide) did not show any tendency to recognize anisole. Cyclolithocholates can, therefore, serve as suitable reference structures in the study of other bile acid derived macrolide~ [~]. As a continuation of our previous study, we now wish to report a 'H-NMR investigation into the interaction of ferrocene (dicyclopentadienyliron) with five bile acid triolides: 3a-hydroxy-5P-cholan-24-oic acid triolide (l), 3u-hydroxy-7-oxo-5~-choIan-24-oic acid triolide (2), 3a-hydroxy-12-0x0-5P-cholan-24-oic acid triolide (3), 3a-hydroxy-7a-TFA-5P-cholan-24-oic acid triolide (4) and 3a-hydroxy-12a-TFA-5P-cholan-24-oic acid triolide (5).Ferrocene is selected as a guest molecule for several reasons: (i) it is a typical metallocene, having a 3-D molecular structure, (ii) ferrocene derivatives have been used as templating agents in the synthesis of bipyridium-based cyclophanesL4], and (iii) ferrocene itself has been frequently used as a guest molecule in a 1 : 1 second-sphere adduct with tetracationic cycl~phane [~] and in many cyclod...
