Acetylene and terminal alkyne complexes of copper(i) supported by fluorinated pyrazolates: syntheses, structures, and transformations. Issue 42 (11th September 2019) - Parasar, Devaborniny
Abstract : A variety of isolable, 2 : 1 and 1 : 1 copper(i )–alkyne complexes of containing pyrazolate ligand supports are presented as well as the copper pyrazolate mediated acetylenic C–H and alkyne CC bond functionalizations. Abstract : Trinuclear {μ-[3, 5-(CF3 )2 Pz]Cu}3 reacts with acetylene to produce the 2 : 1 copper(i ) acetylene complex, Cu4 (μ-[3, 5-(CF3 )2 Pz])4 (μ-HCCH)2 . Related Cu4 (μ-[4-Br-3, 5-(CF3 )2 Pz])4 (μ-HCCH)2 and Cu4 (μ-[4-Cl-3, 5-(CF3 )2 Pz])4 (μ-HCCH)2 have also been isolated using the corresponding copper(i ) pyrazolate and acetylene. The 1 : 1 adducts Cu2 (μ-[3, 5-(CF3 )2 Pz])2 (HCCH)2 and Cu2 (μ-[4-Br-3, 5-(CF3 )2 Pz])2 (HCCH)2 are significantly less stable to the acetylene loss and can be observed in solution at low temperatures under excess acetylene. The X-ray crystal structures of 2 : 1 and 1 : 1 complexes, Cu4 (μ-[3, 5-(CF3 )2 Pz])4 (μ-HCCH)2 and Cu2 (μ-[4-Br-3, 5-(CF3 )2 Pz])2 (HCCH)2 are reported. Raman data show a reduction in  CC stretching frequency by about ∼340 and ∼163 cm −1 in the 2 : 1 and 1 : 1 Cu(i )/acetylene complexes, respectively, from that of the free acetylene. Copper(i ) pyrazolate complexes of the terminal alkynes, phenylacetylene, 1, 8-nonadiyne, and 1, 7-octadiyne are also reported. They form adducts involving one copper atom on each alkyne moiety. The {μ-[3, 5-(CF3 )2 Pz]Cu}3 is also a very versatile and competent catalyst for alkyne transformations as evident from its ability to catalyze the alkyne C(sp)–H bond carboxylation chemistry with CO2, azide–alkyne cycloadditions leading to 1, 2, 3-triazoles including the use of acetylene itself as a substrate, and thiol addition to phenylacetylene affording vinyl sulfides.