Cu(I) Complexes of Pincer Pyridine-Based N-Heterocyclic Carbenes with Small Wingtip Substituents: Synthesis and Structural and Spectroscopic Studies

Abstract

Six new Cu(I) complexes with pincer N-heterocyclic carbene (NHC) ligands of the type 2,6-bis(3-alkylimidazol-2-ylidene)pyridine, I(R), and 2,6-bis(3-alkylimidazol-2-ylidene)methylpyridine, I(R), where R = Me, Et, and Pr have been synthesized using Cu precursors and bis(imidazolium) salts. All of these compounds, namely, [Cu(IMe)](PF), 1; [Cu(IEt)](PF), 2; [Cu(IPr)](PF), 3; [Cu(IMe)](PF), 4; [Cu(IEt)](PF), 5; and [Cu(IPr)](PF), 6, have been characterized by H andC NMR spectroscopies, elemental analysis, solution conductivity, and electrochemical studies. Single crystal X-ray structures were obtained for all complexes except 1. The crystallographic data reveal a binuclear structure containing two Cu atoms at a close distance, 2.622-2.811 Å for all the complexes except 5, which shows a unique mononuclear structure. Spatial syn arrangement of ethyl groups and extensive π-π stacking in the solid state accounts for the mononuclear structure of complex 5. A pseudolinear coordination geometry about metal centers consisting of two Cu-carbene bonds, as well as weak Cu-pyridine interactions, exist among all the complexes independent of their ligand. Solution-state conductivity data reveal a dominant 1:2 electrolyte behavior for 1-3 but 1:1 electrolyte for 4-6, consistent with the sustainable binuclear structure in solutions of Cu(I)-I(R) complexes. Cyclic voltammetry and differential pulse voltammetry studies reveal an irreversible and two quasi-reversible peaks for the one-electron oxidation of solvent-bound and solvent-free binuclear and mononuclear Cu-NHC species in complexes 1-3. In contrast, the reversible Cu(II)/Cu(I) couples of 4-6 at potentials close to that of complexes with tripodal polydentate NHC scaffolds indicate the electronic and structural flexibility of I(R) ligands to accommodate both Cu(I) and Cu(II) ions.

Fine‐Tuning: Advances in Chlorine‐Free Blue‐Light‐Generating Pyrotechnics

“…Domyati et al reported on copper(I) complexes with pincer N ‐heterocyclic carbene (NHC) ligands starting from the reaction of [Cu(MeCN) 4 ]PF 6 or [Cu(MeCN) 4 ]SbF 6 and an in situ generated NHC at room temperature in the absence of air and moisture . Consequently, other tetrakis(acetonitrile) copper(I) complexes with varying anions are known, which might serve as starting materials for simple metathesis reaction to obtain [Cu(MeCN) 4 ]IO 4 .…”

Hybrid Surfactants with N‐Heterocyclic Carbene Heads as a Multifunctional Platform for Interfacial Catalysis

“…When the coordination geometry of the metal center is different, for example octahedral as for Fe 2+ ( 6 bii ) or linear as for Ag + ( 6 biv ), molecular species containing two NHC ligands are obtained (see also the Supporting Information, Figure S5). Similar coordination modes were also found in the literature for conventional, non‐amphiphilic ligands …”

“…Similarc oordination modes werea lso found in the literature for conventional, non-amphiphilic ligands. [20] The self-assembly behavior of the new,h ybrid surfactants 6a,bi was investigated next. We learnedf rom SAXS measurements (Figure 1e)t hat the presence of the metal has am arked effect on the structure of the LC phases.…”

Dinuclear N-heterocyclic carbene copper(I) complexes

“…In all species, the nitrogen atoms of the pyridine are directed towards the metal centers and their distances, ranging from 2.4220(18) Å to 2.8298(18) Å, reveal a weak interaction between these two atoms. Recently, Tahsini and co-workers demonstrated that the formation of this type of dinuclear complexes is only possible when the NHCs are directly bound to the pyridine ring, whereas mononuclear complexes are formed when a methylene spacer between the two moieties is present [67]. Reddy and co-workers further extended this family of complexes by reporting carbaphosphazene derivatives (Scheme 33) [68].…”