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

Dalton Transactions Pub Date: 2019-09-05 DOI: 10.1039/C9DT03350E

Abstract

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.

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