Toward high-generation rotaxane dendrimers that incorporate a ring component on every branch: Noncovalent synthesis of a dendritic [10]pseudorotaxane with 13 molecular components

Abstract

By taking advantage of the fact that cucurbit[6]uril (CB[6]) forms exceptionally stable host-guest complexes with protonated amines, and that its homologue CB[8] can encapsulate a pair of electron-rich and electron-deficient guest molecules to form a stable 1:1:1 complex, we synthesized a novel dendritic [10]pseudorotaxane, or second-generation rotaxane dendrimer (from a topological point of view), in which 1.3 molecular components are held together by noncovalent interactions. A triply branched molecule containing an electron -deficien t bipyridinium unit on each branch formed a branched [4]pseudorotaxane with 3 equivalents of CB[8]. Addition of 3 equivalents of 2,6-dihydroxynaphthalene produced a first-generation rotaxane dendrimer, which was characterized by NMR spectroscopy and CSI-MS. The reaction of the branched [4]pseudorotaxane with 3 equivalents of a triply branched molecule that has an electron-donor unit at one arm and CB [6]-containing units at the other two gave the dendritic [10]pseudorotaxane, the structure of which was confirmed by NMR spectroscopy, UV/Vis titration experiments, and CSI-MS.