Tris(3,5-dimethylpyrazolyl)methane copper(I) complexes featuring one disubstituted cyanamide ligand

The complexes [Cu{HC(3,5-Me ₂pz) ₃}(NCNR ₂)][BF ₄] (1–8; R ₂ = Me ₂ 1, Et ₂ 2, C ₅H ₁₀ 3, C ₄H ₈O 4, C ₄H ₈ 5, C ₃H ₆C ₆H ₄ [NC ₃H ₆C ₆H ₄ is 1,2,3,4-dihydroisoquinoline-2-yl] 6, (CH ₂Ph) ₂ 7, (Me)Ph 8) were prepared by the reaction of [Cu(NCMe) ₄][BF ₄] with HC(3,5-Me ₂pz) ₃ and NCNR ₂ (CH ₂Cl ₂, 20–25 °C) and these species were characterized by C, H, N analyses, high resolution mass-spectrometry with electrospray ionization, ¹H, ¹³C{ ¹H} NMR and FTIR spectroscopic techniques, molar conductivity measurements, thermogravimetry/differential thermal analysis, and also by single-crystal X-ray diffraction for 3. The theoretical topological analysis of the electron density distribution (QTAIM method) together with the NBO analysis were applied to study the nature of Cu–N and Cu–C coordination bonds in [Cu{HC(3,5-Me ₂pz) ₃}(NCNMe ₂)] ⁺, [Cu{HC(3,5-Me ₂pz) ₃}(NCMe)] ⁺, and [Cu{HC(3,5-Me ₂pz) ₃}(CNMe)] ⁺ model species. The nature of Cu–N coordination bonds in [Cu{HC(3,5-Me ₂pz) ₃}(NCNMe ₂)] ⁺ and [Cu{HC(3,5-Me ₂pz) ₃}(NCMe)] ⁺ is very similar, whereas Cu–C contact in [Cu({HC(3,5-Me ₂pz) ₃}(CNMe)] ⁺ is relatively more covalent. The calculated vertical total energies for the Cu–N and Cu–C coordination bonds cleavage increase in the following row: [Cu{HC(3,5-Me ₂pz) ₃}(NCMe)] ⁺ (36 kcal/mol) < [Cu{HC(3,5-Me ₂pz) ₃}(NCNMe ₂)] ⁺ (41 kcal/mol) < [Cu{HC(3,5-Me ₂pz) ₃}(CNMe)] ⁺ (47 kcal/mol), and these theoretical data are coherent with the experimental observations.