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Molecular Recognition with Ditopic Cavitand Re Complexes
Author(s) -
Busi Marco,
Cantadori Barbara,
Boccini Francesca,
De Zorzi Rita,
Geremia Silvano,
Dalcanale Enrico
Publication year - 2011
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.201001668
Subject(s) - cavitand , chemistry , phosphonate , molecular recognition , cooperativity , stereochemistry , supramolecular chemistry , medicinal chemistry , molecule , organic chemistry , biochemistry
The synthesis of a series of cavitand receptors bearing increasing numbers of phosphonate groups at their upper rims and of the corresponding Re‐based ditopic complexes is reported. The molecular recognition properties of these phosphonate cavitands towards both monotopic and ditopic N ‐methylpyridinium salts were investigated. The numbers and spatial dispositions of P=O units are pivotal for the complexation of guest ions. The removal of a single P=O bridge from the parent tetraphosphonate cavitand was sufficient to reduce the association constant by almost three orders of magnitude. Elimination of a second P=O unit completely abolished complexation in the AC distal isomer, both in monotopic and in ditopic hosts. The preorganised structure obtained by interconnection of two triphosphonate cavitands through a Re system showed moderate positive self‐assembly cooperativity in the inclusion of ditopic N ‐methylpyridinium salts in both polar and nonpolar solvents. The speciation profile in ethanol indicates that the clamshell 1:1 complex is dominant at low concentrations (< 10 –4 M ) whereas the 1:2 complex is preferred at higher concentrations of ditopic guest.