| Abstract |
The homoleptic copper(I) complexes [Cu(NCNRR )(4)](BF4) (R/R = Me/Me 1, Et/Et 2, C5H10 3, C4H8O 4, C4H8 5, C3H6C6H4 6, CH2Ph/CH2Ph 7, Me/Ph 8) featuring disubstituted cyanamides were obtained in excellent (92-97\%) yields by the reaction of [Cu(NCMe) 4](BF4) and 4 equivalents of NCNRR . Complexes 1-8 were characterized by atomic absorption spectrometry (Cu\%), high resolution ESI+-MS, molar conductivities, TG/DTA, and H-1, C-13\1H\ NMR, FTIR spectroscopic techniques, and also by single-crystal X-ray diffraction (1, 3, and 4). Results of DFT calculations and X-ray structure determinations reveal that equilibrium geometries of [Cu(NCMe)(4)](+) and [Cu(NCNMe2)(4)](+) in the gas phase are normal tetrahedral (Td)and significantly distorted, respectively. Effects of crystal packing influence the values of the Cu-N-C angles in [Cu(NCNRR )(4)](+), which points out to the noticeable contribution of the heterocumulene mesomeric form for the dialkylcyanamide copper(I) complexes. The QTAIM and NBO analyses indicate that relatively weak Cu-N contacts (15-31 kcal mol(-1)) in both cases exhibit single bond character and clearly polarized toward the N atom (by 91-95\%). The CDA shows that the \M\ <- L sigma-donation substantially prevails over the \M\ -> L pi-back-donation in both [Cu(NCMe)(4)](+) and [Cu(NCNMe2)(4)](+). The orbital, charge, and vibrational frequency arguments as well as inspection of the FTIR data suggest that the electrophilic activation of the N equivalent to C group in homoleptic nitrile and dialkylcyanamide copper(I) complexes is similar, and the different behavior of nitriles and cyanamides in the 1,3-dipolar cycloaddition of ketonitrones is mainly due to the difference in the atomic charges. |
