Comparing the impact of different supporting ligands on copper(I)–ethylene interactions

Abstract The nature of copper(I)–ethylene bonding in a series of [Cu(L)(C 2 H 2 )] n + complexes (where L = 1,4,7-trithiacyclononane, 2,2′-bipyridine, N , N , N ′, N ′-tetramethylethylenediamine, 1,4,7-trimethyl-1,4,7-triazacyclononane, hydrotris(3,5-dimethyl-1-pyrazolyl)borate, the bis(2,6-dimethylphenyl)-substituted s-diketiminate, and the iminophosphanamide (tBu) 2 P(NSiMe 3 ) 2 ) has been studied using density functional theory methods. The B3LYP, M06-L, and BP86 functionals performed similarly in reproducing important geometric parameters from experimental structures. Bonding interactions between the [Cu(L)] n + and ethylene fragments were investigated using energy decomposition analysis (ALMO–EDA), molecular orbital and fragment orbital interaction analysis, and natural bond orbital (NBO) analysis. NBO and EDA calculations both predict an increase in [Cu(L)] n +  → ethylene(π ∗ ) charge donation and stabilization with an increase in the qualitatively-predicted electron donating ability of the supporting ligand, and a lesser amount of ethylene(π) → Cu charge donation, the magnitude of which is not strongly correlated to ligand donor ability. Molecular orbital analysis reveals an increased mixing of the empty ethylene π ∗ -orbital with filled orbitals as the qualitative ligand donating ability increases, consistent with enhanced Cu → ethylene(π ∗ ) π-backbonding and the NBO and EDA results.