Multidentate Lewis-acid host

For a summary of published reports on anion complexation by multidentate Lewis acid hosts, see [3a]. 

An easily visualised example is the multidentate Lewis-acid host 2.77, a colourimetric fluoride sensor. The receptor contains a non-irmocent ferrocenyl linker between the boronate groups. Reaction of 2.77 with n-Bu4N+F in CHCI3... 

Yang, X. G., Knobler, C. B., Zheng, Z. P., Hawthorne, M. F., Host-guest chemistry of a new class of macrocyclic multidentate lewis-acids comprised of carborane-supported electrophilic mercury centers. J. Am. Chem. Soc. 1994,116, 7142-7159. 

Hawthorne. M.F. Zheng, Z. Recognition of electron-donating guests by carborane-supported multidentate macrocyclic Lewis acid hosts Mercuracarborand chemistry. Acc. Chem. Res. 1997. 30. 267-276. 

Nadeau, F. Simard. M. Wuest, J.D. Multidentate Lewis acids. Complex of a macrocyclic host with a bidentate guest. Organometallics 1990. 9. 1311-1314. 

In this way hosts 141-145 with both a cr-bonded Lewis acidic boron atom for complexation of anions and a conventional multidentate ligand for cations are generated. Complexation experiments of the 21-membered crown [6] boronate 142 with different potassium salts KX (X = F, Cl, Br, I, SCN, CN, OMe) indicate that there is a high specificity for the incorporation of KF, whereby F is bound covalently to the boron atom and is complexed by the crown ether (146, Fig. 39). An X-ray study has shown that the complexation of KF is heterotopic, i.e., both ions are complexed inside the same host. Some of the salts can only be bound in a monotopic way (KI and KSCN) [237]. 

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