LCu(μ-X)2CuL compounds: An induced cuprophilic interaction

Abstract

A trio of dimeric copper(I) complexes of the formula [(Ph3P)Cu(μ-X)2Cu(PPh3)] (X=OC6F5, 1, OC4F9, 2, OCPh(CF3)2, 3) were prepared and characterized by X-ray crystallography, elemental analysis, and NMR spectroscopy (1H, 13C, 19F, 31P), as was the monomeric [(cy3P)Cu(OC4F9)] (cy=cyclohexyl, 4). Solution conductivity studies demonstrate that all three new dinuclear compounds, as well as the known [(Ph3P)Cu(μ-OC4H9)2Cu(PPh3)], 2-H, are neutral species in solution and do not rearrange into ion pairs. The fold angle (β) varies among these four dimers and the Cu(I)⋯Cu(I) distance in the structure of 2, 2.8315(5)Å, is cuprophilic. The Cu(I)⋯Cu(I) distances for 1, 2-H, and 3 are 3.0533(5), 2.890(2), and 3.0169(6)Å respectively. Density functional theory (DFT) calculations were performed on 1, 2, 3, and 2-H, as well as the hypothetical 1-H, and several related models. Five PMe3 models, 1(Me), 1-H(Me), 2(Me), 2-H(Me), and 3(Me) were also studied as well as five monomers [(Me3P)CuX] 1-mon, 1-H(mon), 2-mon, 2-H(mon), and 3-mon to understand the electronic reasons for folding in this group of compounds. A Natural Energy Decomposition Analysis (NEDA) indicates that electrostatic stabilizations are the dominant factor governing the strength of interaction between monomeric fragments in 1(Me)–3(Me). NBO analysis reveals that 1(Me) and 1-H(Me) do not display any cuprophilic interactions. The folding angle observed in 2(Me), 2-H(Me), and 3(Me), which is correlated with an increased delocalization from the oxygen 2pz lone pairs, brings the metal centers into sufficient propinquity to have weak Cu⋯Cu orbital interactions. Weak luminescence behavior at room-temperature is also consistent with these assignments.