AEI 98 |
| Donor-acceptor [2]catenanes based on the tetracationic cyclobis(paraquat-p-phenylene) (CBPQT4+) π-acceptor component are showing considerable promise in devices, ranging in diversity from electronic paper to molecular switches. Their preparation has traditionally been based on the synthesis of a donor-containing macrocycle, followed by the clipping of the CBPQT4+ ring around a 1,5-dioxynaphthalene or tetrathiafulvalene recognition site. Recently, we developed two conceptually novel approaches to these compounds. In the first, kinetically controlled threading-followed-by-clipping, the donor thread complexes the preformed acceptor ring and then cyclizes around it, affording the [2]catenane. Copper-catalyzed Huisgen 1,3-dipolar cycloaddition and Eglinton coupling are used as tools for the final catenation step. An alternative – and arguably more elegant – method for templating the synthesis of donor-acceptor [2]catenanes is based on thermodynamically controlled dynamic nucleophilic substitution. It starts with preformed individual donor and individual acceptor rings and interlocks them into a [2]catenane in a single step in the presence of NBu4I. Mechanistically, NBu4I acts as a homogenous nucleophilic catalyst which opens up the acceptor ring. Coordination of the “opened acceptor” with the donor component into a charge-transfer complex follows. Another nucleophilic reaction reseals the acceptor ring, expelling the iodide in the process and providing the [2]catenane cleanly and in high overall yields. The reaction rate is general in scope and can be used to either synthesize or interconvert different [2]catenanes. The molecular analog of the magician's trick in which two rings “magically” become interlocked, will likely turn into a powerful synthetic tool that would facilitate the production of novel catenanes, and bring their applications within closer reach.
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Academic Employment Initiative
8:00 PM-10:00 PM, Monday, August 20, 2007 BCEC -- Exhibit Hall - B2, Sci-Mix
Academic Employment Initiative |
