Nature of the chemical bonding and electronic structure of dicoordinated copper(I) complexes of alkenes, alkynes, and NHC ligands: a DFT overview

A DFT (density functional theory) investigation using the generalized gradient approximation BP86 and the hybrid B3LYP functionals and TZP basis set is dealing with the bonding, the electronic structure and the interaction types occurred within the XCuL’ and (LCuL’)⁺ (X = Cl, CH₃, CN, CF₃, L = CO, NH₃, PH₃, and L’ = C₂H₂, C₂H₄, C₄H₆, C₆H₆, and NHC) complexes. The optimized structures and energy decomposition analysis of XCuL’ and (LCuL’)⁺ complexes were employed to provide a relationship between the bond lengths, the X-Cu-L’ and L-Cu-L’ bond angles, the Wiberg indices, the Mayer bond orders, interaction energies, and the Cu-L’ bonding character. The energy decomposition analysis indicates that the interactions occurred for various L’ ligands are more electrostatically than covalently bonded to the Cu(I) center formally of + I oxidation state. The different contributions stemming from electrostatic and orbital interactions are significant, in relationship with the ionic and covalent characters, respectively. The contribution from σ-donation to the bonding energy was found more important for the NHC ligand than the alkene and alkynes ones. However, the contribution from π-back-donation was found to be comparable for all complexes. The σ-bonding contributes more than 50% into the total orbital interaction overtaking those of π type, in accordance with the population of the copper 4s orbital, particularly in the presence of C₆H₆ and NHC ligands. The interactions in all complexes exhibit comparable deformation densities and NOCV orbital shapes. Besides, it has been shown that the ΔE_prep contributes weakly in the deformation of the interacting fragments as well as the BSSE correction which impacts weakly or negligibly the interactions between the fragments composing different XCuL’ and (LCuL’)⁺ complexes.