Cavitand complex

When the guest used is p-nitrophenylcholine carbonate (PNPCC) the Lewis acid zinc(n) activates the well-positioned carbonyl group in the P PCC Zn-cavitand towards reactions with external nucleophiles. The energy minimized structure of the PNPCC Zn-cavitand complex shows that cation-n interactions and C —O -Zn coordination bond occurs simultaneously. 

The first approach to the formation of a ditopic cavitand complex has been reported by Sorrell et al. [56]. They identified the tri-bridged resorcinarene as a... 

Figure 7.19 C/s-ditopic cavitand complex 47 and its crystal structure (side view). Reproduced with permission from Ref. [57].

The potential of ditopic cavitand complexes to bind ditopic guests has been demonstrated by Rebek and coworkers using cavitand 53 as monodentate ligand (Scheme 7.13) [58]. Cavitand 53 combines the advantages of a deep vase-like cavity obtained through a network of hydrogen bonds and the presence of a tolylpyridyl group able to coordinate to the metal center. The ditopic complex 54 forms quanti-... 

In 1998 Harrison reported the synthesis and characterization of water-soluble, dynamic, cobalt-coordinated carcerand 16 (Fig. 9.7) [64]. A follow-on study 7 years later found that 16 can entrap a range of guests [65]. Competition studies revealed that anisole and p-xylene were the strongest binders both had an encapsulation preference 20,000 times stronger than the poorest guest, m-xylene. Harrison extended this work using the same cavitand complexed with Fe (II) [66]. The resulting carcerands were also water-soluble and were found to contain six waters. In the presence of bromobenzene-saturated water, the aromatic preferentially bound. 

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