Synthesis of [3]rotaxanes that utilize the catalytic activity of a macrocyclic phenanthroline-Cu Complex: remarkable effect of the length of the axle precursor.

[3]Rotaxanes, which consist of one macrocyclic phenanthroline compound and two axle components, were prepared by the oxidative dimerization of an alkyne compound with bulky tris[4'-cyclohexyl-(1,1'-biphenyl)-4-yl]methyl blocking group. The catalytic activity of a macrocyclic phenanthroline-Cu complex was utilized to thread the two axle components inside the ring. The alkyne compound with chain of 15 or 20 methylene groups gave [3]rotaxanes in high yields, whereas the axle with a chain of six methylene groups afforded a [3]rotaxane in very poor yield. We also examined the effect of the ring size on the synthesis of [3]rotaxanes. [3]Rotaxanes were not isolated when a macrocyclic phenanthroline compound with a smaller ring size was used.