Efficient and environmentally friendly Glaser coupling of terminal alkynes catalyzed by multinuclear copper complexes under base-free conditions

An efficient catalytic system with dinuclear complex [Cu-2(ophen)(2)] 1 and tetranuclear complex [Cu-4(ophen)(4)(tp)](2) as catalysts has been developed for the Glaser coupling reaction, which adopts environmentally friendly water as the solvent at room temperature under air/O-2 atmosphere and avoids the utilization of any base. Satisfyingly, due to its poor solubility in common solvents, tetranuclear compound 2 served as a molecular heterogeneous catalyst and could be reused five times without loss of activity. Both catalysts could be prepared in high yield via simple hydrothermal reactions with cheap ligands, which in combination with the environmentally friendly water medium and mild catalytic reaction conditions makes the approach accord with the concept of green chemistry in the synthesis of 1,3-diynes.