Catalytic coupling of terminal alkynes by silica supported Cu(II) complex

Diacetylenes are important compounds in organic chemistry. This compounds have variousapplications in the fields of organic synthesis, material science, pharmaceuticals and medicine. Coupling ofterminal alkynes is one of the important methods for the synthesis of diacetylenes [۱]. There are severalmethods for coupling of terminal alkynes to prepare diacetylene and one of them is the use of copper catalystsand Cu(I) or Cu(II) salts [۲]. In recent years, the use of recyclable, effective and green catalysts in the chemicalindustry has received much attention, the purpose of using a heterogeneous catalyst is the reuseability of thecatalyst and this is one of the important issues in green chemistry. Although copper complexes are active inthe coupling of terminal alkynes, these compounds mainly forms homogeneous systems. Neverthless, theycan be heterogenised by using special synthetic strategies like supporting on the surface of silica gel. In thisproject, a new Cu(II) complex with general formula of [Cu(HL)(NO۳)(CH۳OH)]∙CH۳OH, was synthesized by thereaction of (E)-۴-amino-N'-(۲-hydroxy-۳-methoxybenzylidene)benzohydrazide (H۲L) with Cu(NO۳)۲∙۳H۲O inmethanol. The ligand and copper complex were characterized by elemental analysis and spectroscopicmethods. The structure of copper complex was determined by single crystal X-ray analysis and the resultsindicated that it has a free amine functionality. Therefore, the obtained complex was supported on silica gelby using its reaction with propionyl chloride-functionalized silica gel. The resulting heterogeneous catalyst wascharacterized by various methods including FT-IR, TGA, DRS, EPR, EDS, SEM, XRD, XPS analyses and wasempolyed as a catalyst in carbon-carbon coupling reaction. The results indicated that this heterogeneouscatalyst is an active catalytic system for coupling of terminal alkynes. The structure of the catalytic productwas also determined by single crystal X-ray analysis which is shown in Fig. ۱. The results showed that theheterogeneous supported catalyst has also high stability and can be used several times for catalytic C-Ccoupling reaction

Keywords:

Copper complex , Heterogeneous catalyst , C-C coupling reaction , Terminal alkynes