New Cu(I) complexes with pincer pyridine-based N-heterocyclic carbene (NHC) ligands of the type I(R)CNC, and I(R)C^N^C where R = Me, Et, iPr, and tBu have been synthesized. All the compounds (1–7) have been characterized by 1H- and 13C NMR spectroscopies, elemental analysis, solution conductivity, and electrochemical studies. Single crystal X-ray data were obtained for all complexes, except Cu-IMeCNC revealing a binuclear structure of two Cu atoms at a close distance, 2.622–2.811 Å for all complexes except Cu-IEtC^N^C. Solution-state conductivity data reveal a dominant 1:2 electrolyte behavior for Cu(I)-I(R)CNC, but 1:1 electrolyte for Cu-I(R)C^N^C, consistent with the sustainable binuclear structure in solutions of Cu(I)-I(R)CNC complexes. Cyclic voltammetry and differential pulse voltammetry studies reveal an irreversible and two quasi-reversible peaks for the 1e- oxidation of solvent-bound/solvent-free binuclear and mononuclear Cu-NHC species in 1–3. In contrast, the reversible Cu(II)/Cu(I) couples of 4–7 at potentials close to that of complexes with tripodal polydentate NHC scaffolds indicate the electronic and structural flexibility of I(R)C^N^C ligands to accommodate both Cu(I) and Cu(II) ions. The complexes 4–7 were utilized as catalysts in the C-C bond formation of sp- and sp2-hybridized carbon atoms (Sonogashira reaction) and 60 -95% isolated yield of cross-coupled product was obtained in the absence of any Pd additives.

Synthesis, structural properties and catalytic application of pincer N-heterocyclic carbene complexes of copper(I) with small wingtip substituents

254th National Meeting (2017)

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