Template-directed Synthesis of Novel Supramolecular Architectures

Abstract

The ability of a dibenzylammonium dumbbell to form [2]rotaxanes with less than [24]crown ethers have been investigated in order to correlate the spatial requirement of the ammonium moiety in dibenzylammonium ion with the size of the encircling crown ether. The investigation hinges on template-directed ring-closing olefin metathesis using 2nd generation Grubbs catalyst, known as the clipping approach. A series of acyclic diolefin polyethers were independently subjected to the ring-closing metathesis in the presence of dibenzylammonium hexafluorophosphate, resulting in the formation of six [2]rotaxane molecules incorporating unsaturated and saturated [20], [21] and [22]crown ethers onto the ammonium moiety of dibenzylammonium ion. In addition, three 1: 1 pseudorotaxane complexes were generated between dibenzylammonium ion and three different [23]crown ethers, with reasonably high association constant values. Moreover, attempts to synthesize [2]rotaxane on dibenzylammonium ion motif with even smaller cavity-sized [19]crown ethers were made, which however failed. Subsequently, the smallest stopper group has been investigated, which is found to be trifluoromethyl group, effectively stoppering unsaturated [20]crown ether in a [2]rotaxane. We also report the template-directed synthesis of a well-defined, homogeneous, kinetically and thermodynamically stable [5]molecular necklace by ¿threading-followed-by-ring-closing-metathesis¿ approach.