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

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.

Four new [LCu(I)X] compounds have been prepared, one of which is noticeably folded. The faint cuprophilic interaction does not cause the fold, but rather the varying O–Cu electrostatic interactions control the fold, and when the dimer fold angle is narrow enough, the two Cu atoms can interact in a metallophilic fashion.Figure optionsDownload as PowerPoint slide