Acetylene and terminal alkyne complexes of copper(i) supported by fluorinated pyrazolates: syntheses, structures, and transformations.

Trinuclear {μ-[3,5-(CF3)2Pz]Cu}3 reacts with acetylene to produce the 2 : 1 copper(i) acetylene complex, Cu4(μ-[3,5-(CF3)2Pz])4(μ-HC[triple bond, length as m-dash]CH)2. Related Cu4(μ-[4-Br-3,5-(CF3)2Pz])4(μ-HC[triple bond, length as m-dash]CH)2 and Cu4(μ-[4-Cl-3,5-(CF3)2Pz])4(μ-HC[triple bond, length as m-dash]CH)2 have also been isolated using the corresponding copper(i) pyrazolate and acetylene. The 1 : 1 adducts Cu2(μ-[3,5-(CF3)2Pz])2(HC[triple bond, length as m-dash]CH)2 and Cu2(μ-[4-Br-3,5-(CF3)2Pz])2(HC[triple bond, length as m-dash]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)2Pz])4(μ-HC[triple bond, length as m-dash]CH)2 and Cu2(μ-[4-Br-3,5-(CF3)2Pz])2(HC[triple bond, length as m-dash]CH)2 are reported. Raman data show a reduction in [small nu, Greek, macron]C[triple bond, length as m-dash]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)2Pz]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.