Abstract
Access to readily functionalized ligand architectures is of crucial importance in a range of different areas including catalysis, metallopharmaceuticals, bioimaging, metallosupramolecular chemistry, mechanically interlocked architectures, and molecular machines. The mild and modular Cu(I)-catalyzed 1,3-cycloaddition of terminal alkynes with organic azides (the CuAAC “click” reaction) allows the ready formation of functionalized 1,4-disubstituted-1,2,3-triazole scaffolds, and this has led to an explosion of interest in the coordination chemistry of these heterocycles. The parent 1,4-disubstituted-1,2,3-triazole units can potentially act as monodentate or bridging ligands. Examples of both the monodentate (through either the N3 nitrogen or C5 carbon positions of the 1,2,3-triazole) and bridging (through the N2 and N3 nitrogen atoms) coordination modes have been structurally characterized. A diverse array of bi-, tri-, and polydentate ligands incorporating 1,4-disubstituted-1,2,3-triazole units have also been synthesized and characterized. When the chelate pocket involves coordination through the N3 nitrogen atom of the 1,2,3-triazole, these are called “regular” click ligands. While these are the most common type of “click” chelate, “inverse” ligands in which the 1,2,3-triazole unit coordinates through the less electron-rich N2 nitrogen atom have also been synthesized and characterized. The resulting “click” complexes are beginning to find applications in catalysis, metallosupramolecular chemistry, photophysics, and as metallopharmaceuticals and bioimaging agents.