With a dinuclear macrocycle 2 that contains weak reversible OsVI-N coordinate bonds, self-assembly and equilibrium dynamics of - and rotaxanes have been investigated. When the macrocycle 2 was mixed together with threads 4a-e, which all contain an adipamide station but different sizes of end groups, pseudorotaxane- and rotaxane-like complexes were immediately formed with large association constants > of 7 × 103M-1 in CDCl3 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 4a and 16.7 kcal mol-1 for 4d, and indicate that the slipping process is at least one order of magnitude faster than the clipping process. Using threads 13a and 13b that contain two adipamide groups, more complicated systems have been investigated in which rotaxane, rotaxane, and free components are in equilibrium. Concentration- and temperature-dependent 1H 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, rotaxane, and rotaxane are 30, 45, and 25%, respectively, in a mixture of 2 (2mM) and 13a (2mM) in CDCl3, at 10°C. However, rotaxane exists nearly quantitatively in a mixture of 2 (4mM) and 13a (2mM) in CDCl3 at a low temperature - 10°C.
|Number of pages||11|
|Journal||Chemistry - A European Journal|
|Publication status||Published - 2001 Jun 18|
All Science Journal Classification (ASJC) codes
- Organic Chemistry