cis -1,2-Bis(diphenylphosphino)ethylene copper( i ) catalyzed C–H activation and carboxylation of terminal alkynes

The reaction of cis -1,2-bis(diphenylphosphino)ethylene (dppet) with CuX (X = CN, SCN) in 1 : 1 M molar ratio in DCM–MeOH (50 : 50 V/V) under refluxing conditions gave two dimeric Cu( i ) complexes, viz. [Cu 2 (μ-CN) 2 (κ 2 - P , P -dppet) 2 ] ( 1 ) and [Cu 2 (μ 2 -SCN) 2 (κ 2 - P , P -dppet) 2 ] ( 2 ). These complexes have been characterized by elemental analyses, IR, 1 H and 31 P NMR, and electronic absorption spectroscopies, and ESI-MS. The molecular structure of 2 was confirmed by single crystal X-ray diffraction, which indicated that 2 exists as a centrosymmetric dimer in which the two copper centers are bonded to two dppet ligands and two bridging thiocyanate groups in a μ 2 -manner. The electrochemical properties of 1 and 2 were studied by cyclic voltammetry. Both the complexes exhibited strong luminescence properties in the solution state at ambient temperature. Both the complexes were found to be efficient catalysts for the conversion of terminal alkynes into propiolic acids with CO 2 . Owing to their excellent catalytic activity, the reactions proceed at atmospheric pressure and ambient temperature (25 °C). The catalytic products were obtained in excellent yields (90–97%) by using the complex loading of 1 mol%.