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Self‐Assembly and Dynamics of [2]‐ and [3]Rotaxanes with a Dinuclear Macrocycle Containing Reversible Os−N Coordinate Bonds
Author(s) -
Chang SungYoun,
Choi Jeung Soon,
Jeong KyuSung
Publication year - 2001
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/1521-3765(20010618)7:12<2687::aid-chem26870>3.0.co;2-a
Subject(s) - rotaxane , slipping , chemistry , crystallography , yield (engineering) , stereochemistry , clipping (morphology) , isomerization , supramolecular chemistry , crystal structure , physics , geometry , thermodynamics , organic chemistry , linguistics , mathematics , philosophy , catalysis
With a dinuclear macrocycle 2 that contains weak reversible Os VI −N coordinate bonds, self‐assembly and equilibrium dynamics of [2]‐ and [3]rotaxanes have been investigated. When the macrocycle 2 was mixed together with threads 4 a – e , which all contain an adipamide station but different sizes of end groups, [2]pseudorotaxane‐ and rotaxane‐like complexes were immediately formed with large association constants of >7×10 3 m −1 in CDCl 3 at 298 K. Exchange dynamics, explored by 2D‐EXSY experiments, suggest that assembly and disassembly of complexes occur through two distinct pathways, slipping or clipping, and this depends on the size of the end groups. The slipping pathway is predominant with smaller end groups that give pseudorotaxane‐like complexes, while the clipping pathway is observed with larger end groups that yield rotaxane‐like complexes. Under the same conditions, exchange barriers (ΔG ≠ ) were 14.3 kcal mol −1 for 4 a and 16.7 kcal mol −1 for 4 d , and indicate that the slipping process is at least one order of magnitude faster than the clipping process. Using threads 13 a and 13 b that contain two adipamide groups, more complicated systems have been investigated in which [2]rotaxane, [3]rotaxane, and free components are in equilibrium. Concentration‐ and temperature‐dependent 1 H NMR spectroscopic studies allowed the identification of all possible elements and the determination of their relative distributions in solution. For example, the relative distribution of the free components, [2]rotaxane, and [3]rotaxane are 30, 45, and 25 %, respectively, in a mixture of 2 (2 m M ) and 13 a (2 m M ) in CDCl 3 at 10 °C. However, [3]rotaxane exists nearly quantitatively in a mixture of 2 (4 m M ) and 13 a (2 m M ) in CDCl 3 at a low temperature −10 °C.