MOF-Supported Copper Complex-Catalyzed Synthesis of Unsymmetrical 1,3-Diynes Without External Additives

Cu complexes supported on metal-organic frameworks (MOFs) with N-1,N-1,N-2,N-2-tetramethylethylenediamine (TMEDA) were prepared via post-synthetic modification, and proved to be highly efficient for Glaser heterocoupling reactions. Compared with some referential catalysts, which were prepared by using a series of copper salts and Cu-0 nanoparticles as the copper sources, the newly designed MIL-101-NH-TMEDA.CuClx exhibited highest catalytic activity and selectivity in the model Glaser heterocoupling reaction. Much lower activity was observed with the homogeneous counterpart, TMEDA.CuCl4. Intriguingly, the Glaser heterocoupling reactions over MIL-101-NH-TMEDA.CuClx catalyst can be conducted without adding external ligands, base, or acid, which are always necessary in the previously reported systems. The dense catalytic active sites in the MOF channels and the adsorption properties of the MOF were conjectured to be partially responsible for the observed high catalytic activity, which may allow the formation of a unique internal environment in the three-dimensional porous framework that significantly boosted progress of the reactions. The X-ray photoelectron spectroscopy (XPS) results showed also that the catalytically active copper species changed from Cu-II to Cu-I after catalytic use.