Self-assembly and dynamics of [2]- and [3]rotaxanes with a dinuclear macrocycle containing reversible Os-N coordinate bonds

With a dinuclear macrocycle 2 that contains weak reversible Os-VI-N coordin ate bonds, self-assembly and equilibrium dynamics of [2]- and [3]rotaxanes have been investigated. When the macrocycle 2 was mixed together with threa ds 4a-e, which all contain an adipamide station but different sizes of end groups, [2]pseudorotaxane- and rotaxane-like complexes were immediately for med with large association constants of > 7 x 10(3) M-1 in CDC1(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-lik e complexes, while the clipping pathway is observed with larger end groups that yield rotaxane-like complexes. Under the same conditions, exchange bar riers (DeltaG(+)) were 14.3 kcal mol(-1) for 4a and 16.7 kcalmol(-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 t wo adipamide groups, more complicated systems have been investigated in whi ch [2]rotaxane, [3]rotaxane. and free components are in equilibrium. Concen tration- and temperature-dependent H-1 NMR spectroscopic studies allowed th e identification of all possible elements and the determination of their re lative distributions in solution. For example, the relative distribution of the free components, [2]rotaxane, and [3]rotaxane are 30, 45, and 25 %,res pectively, in a mixture of 2 (2 mM) and 13a (2 mM) in CDCl3 at 10 degreesC. However, [3]rotaxane exists nearly quantitatively in a mixture of 2 (4 mM) and 13a (2 mM) in CDCl3 at a low temperature -10 degreesC.