Novel combinatorial approach to triazole-based heterobidentate ligands for organometallic catalysis
Written by Elana Slutsky Smith
Elana Slutsky Smith and Mark Gandelman
Schulich Faculty of Chemistry, Technion-Israel Institute of Technology, Technion City, Haifa 32000, Israel
The chemistry of triazole-based systems, which may be constructed by Huisgen 1,3-dipolar cycloaddition, has recently found great interest within the chemical community. This is largely due to the discovery of Sharpless et al that this cycloaddition between azides and terminal alkynes can be carried out under ambient conditions and with exclusive regioselectivity for 1,4-substituted triazole products when mediated by catalytic amounts of Cu(I) salts.[1] Coined the "Click" reaction, it has found many spectacular applications in materials, supramolecular biological and synthetic chemistry. Remarkably, 1,5-substitued triazole regioisomers represent an attractive connective alternative. Interestingly, although a selective procedure for preparation of 1,5-triazoles has been recently published,[2] the chemistry of this direction is far less investigated.
In our group, we have initiated an active program for the design and efficient development of new ligands and metal-based systems for catalysis. We have recognized that the selective assembly of phosphine azides and alkynes in 1,5-regioisomeric fashion would provide us with conceptually new combinatorial approach to bidentate ligands. Here, we describe our findings in this project, including a novel rearrangement of the substituents across the triazole ring.[1] Rostovtsev, V. V., et. al., "A Stepwise Huisgen Cycloaddition Process: Copper(I)-Catalyzed Regioselective 'Ligation' of Azides and Terminal Alkynes." Angew. Chem. Int. Ed. 2002, 41, 2596.
[2](a) Zhang, Li, et. al., " Ruthenium-Catalyzed Cycloaddition of Alkynes and Organic Azides." J. Am. Chem. Soc. 2005, 127, 15998. (b) Krasinski, Antoni, et al., "Direct Synthesis of 1,5-Disubstituted-4-magnesio-1,2,3-triazoles, Revisited.” Org. Let. 2004, 6(8), 1237.