Metal-Organic Frame works: Highly Efficient and Reusable Catalyst for solvent free 1,3-Dipolar Cycloaddition of Organic Azides to Alkynes

1,2,3-Triazoles are ubiquitous structural motifs found in a wide range of biologically active natural products and have various applications in pharmaceuticals, agrochemicals, biochemical, material science. In 2002, the groups of Sharpless and Meldal have independently discovered the highly regioselective Huisgen 1,3-dipolar cycloaddition of an alkyne and an azide catalyzed by Cu(I) species under mild conditions to afford 1,4-disubstituted 1,2,3-triazoles.

However, most of the reported copper-catalyzed azide alkyne cycloaddition reactions are homogeneous and have serious drawbacks such as the difficulty in separation and subsequent use of expensive catalysts and indispensability of additives such as stabilizing ligands and bases.  The development of easily recoverable and recyclable heterogeneous catalysts can solve the problems and has received particular research interest in organic chemistry.

This presentation will report the effort to develop a kind of recently arisen porous material, Metal-Organic Framework (MOF) and its application on regioselective synthesis of 1,2,3-triazoles by 1,3-dipolar cycloaddition of terminal alkynes to organic azides under solvent free conditions. We synthesized a Cu(I) based MOF with open metal site under mild reaction conditions. This protocol has the advantages of excellent yields, low catalyst loading and catalyst recyclability. The catalyst was recovered and reused efficiency up to 5 cycles without major loss of activity. Powder X-ray Diffraction experiment indicates that the crystalline of Cu(I)-MOF could be well maintained after the catalytic reaction. As a result of their high stability, applications of this catalyst to other copper-catalyzed reactions are in progress and will be reported in due course.