Copper(I)-catalyzed azide-alkyne cycloaddition as synthetic tool for triazole-based ligands
Within in the last five years, chemists have identified a wide range of additional applications for the 1H-1,2,3-triazole heterocycle, e.g., synthesizing bidentate 2-pyridyl-substituted 1H-1,2,3-triazole (trzpy) ligands. The system itself is known since 1970 and has been obtained by recyclization of v-triazolo[l,5-a]pyridines. In 1977, Seebach et al. combined non-enolizable nitriles and lithiated nitrosamines providing N1-substituted trzpys. The regioselective copper(I)-catalyzed 1,3-dipolar cycloaddition of 2-ethynylpyridines with organic azides exclusively yields 1,4-substituted trzpys, a very versatile scaffold offering plenty of beneficial properties. This thesis compiles construction, metal coordination chemistry and macromolecular chemistry of trzpy ligands. The regioselective copper(I)-catalyzed 1,3-dipolar cycloaddition between organic azides and terminal alkynes (CuAAC) represented the key step for the preparation of the trzpy-based chelators. The use of the triazole entity provided a facile access to bidentate chelates that can be regarded as analogs to 2,2´-bipyridines. Using the CuAAC as a synthetic tool enabled a convenient functionalization of the trzpy ligands: Reactive functional groups can be directly introduced by designing the organic azide and allow subsequent chemical transformations, such as the application of radical polymerization methods. Furthermore, the CuAAC is able to support the introduction of additional functional moieties at the triazole (providing solubility, introducing substituents) due to its high tolerance to a wide range of reaction conditions and to a large independence on the electronic configuration of the deployed reactants.