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

• Published in: Dalton transactions : an international journal of inorganic chemistry 2019-11, Vol.48 (42), p.15782-15794
• Main Authors: Parasar, Devaborniny, Ponduru, Tharun T, Noonikara-Poyil, Anurag, Jayaratna, Naleen B, Dias, H. V. Rasika
• Format: Article
• Language: English
• Subjects: Acetylene; Adducts; Alkynes; Carboxylation; Chemical bonds; Coordination compounds; Copper; Crystal structure; Crystallography; Fluorination; Hydrogen bonds; NMR; Nuclear magnetic resonance; Organic chemistry; Reaction products; Substrates; Transformations; Triazoles
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/c9dt03350e

Trinuclear {μ-[3,5-(CF 3 ) 2 Pz]Cu} 3 reacts with acetylene to produce the 2 : 1 copper( i ) acetylene complex, Cu 4 (μ-[3,5-(CF 3 ) 2 Pz]) 4 (μ-HC&z.tbd;CH) 2 . Related Cu 4 (μ-[4-Br-3,5-(CF 3 ) 2 Pz]) 4 (μ-HC&z.tbd;CH) 2 and Cu 4 (μ-[4-Cl-3,5-(CF 3 ) 2 Pz]) 4 (μ-HC&z.tbd;CH) 2 have also been isolated using the corresponding copper( i ) pyrazolate and acetylene. The 1 : 1 adducts Cu 2 (μ-[3,5-(CF 3 ) 2 Pz]) 2 (HC&z.tbd;CH) 2 and Cu 2 (μ-[4-Br-3,5-(CF 3 ) 2 Pz]) 2 (HC&z.tbd;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, Cu 4 (μ-[3,5-(CF 3 ) 2 Pz]) 4 (μ-HC&z.tbd;CH) 2 and Cu 2 (μ-[4-Br-3,5-(CF 3 ) 2 Pz]) 2 (HC&z.tbd;CH) 2 are reported. Raman data show a reduction in &z.ngrm; C&z.tbd;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-(CF 3 ) 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 CO 2 , 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. 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&z.tbd;C bond functionalizations.