Synthesis and structural studies of Cu(I) methylthiosalicylate complexes and their catalytic application in thiol-yne click reaction

Three complexes of Cu(I), [Cu(PPh3)(2)(mts)] (1), [Cu(dppf)(mts)] (2) and [Cu(dppe)(mts)](2) (3) (mts = methylthiosalicylate; dppf = diphenylphosphinoferrocene; dppe = diphenylphosphinoethane), have been synthesized and characterized. Complexes 1 and 2 are monomeric, while 3 has a dimeric structure. The coordination geometry around Cu(I) in these complexes are trigonal pyramidal/distorted tetrahedral. The catalytic activities of the complexes towards hydrothiolation of alkynes (via thiol-yne click reaction) have been studied. Out of these three complexes, 2 has been found to be an efficient catalyst for the synthesis of unsymmetrical vinyl sulfide. The desired vinyl sulfides are obtained in good to excellent yields, with up to >99% Z stereoselectivity in one case. This protocol tolerates a wide variety of functional groups or substrates, is palladium-free, and does not require the use of expensive or air-sensitive additives. The scope and versatility of the method have been successfully demonstrated with a few examples.