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Size Complementarity of Macrocyclic Cavities and Stoppers in Amide‐Rotaxanes
Author(s) -
Heim Christiane,
Affeld Ansgar,
Nieger Martin,
Vögtle Fritz
Publication year - 1999
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/(sici)1522-2675(19990505)82:5<746::aid-hlca746>3.0.co;2-c
Subject(s) - rotaxane , chemistry , amide , slipping , steric effects , axle , intramolecular force , crystallography , stereochemistry , supramolecular chemistry , organic chemistry , geometry , crystal structure , mathematics , engineering , mechanical engineering
New [2]rotaxanes were prepared by the threading and the slipping procedure, the latter having the advantage of not needing templating interactions. As a consequence, the first [2]rotaxane consisting of a tetraamide macrocycle and a pure hydrocarbon thread was synthesized (see 12a in Scheme 2 ). Sterically matching wheels and axles being the basic requirement of a successful slipping approach to rotaxanes, mono‐ and bishomologous wheels 5b , c with larger diameters than the parent 5a were synthesized and mechanically connected to amide axles 10a – c which were stoppered with blocking groups of different spatial demand ( Scheme 1 ). The deslipping kinetics of the resulting rotaxanes 8a – c and 9a , b were measured and compared; it emerges that even slight increases in the wheel size require larger stoppers to stabilize the mechanical bond. Moreover, when the deslipping rate of 8a (amide wheel and amide axle) was determined in either DMF or THF, a strong dependence on the solvent polarity, which is caused by a differing extent of intramolecular H‐bonds between the wheel and the axle, was observed. As expected, no such dependence was detected for rotaxane 12a (amide wheel and hydrocarbon axle) whose components cannot interact via H‐bonds. The comparison of the sterically matching pairs of macrocycles and blocking groups, found by a systematic fitting based on the results of slipping and deslipping experiments, with other rotaxane types bearing similar stoppers allows conclusions concerning the relative cavity size of wheels of various structure.