The Unusual Structural Behavior of Heteroleptic Aryl Copper(I) Thiolato Molecules: Cis vs Trans Structures and London Dispersion Effects

A series of heteroleptic aryl copper­(I) thiolato complexes of formula {Cu2(SAr)­Mes}2 (Ar = C6H3-2,6-(C6H2-2,4,6-Me3)2 (ArMe6), 1; C6H3-2,6-(C6H3-2,6-iPr2)2 (AriPr4), 2; C6H3-2,6-(C6H2-2,4,6-iPr3)2 (AriPr6), 3) and {Cu4(SAr)­Mes3} (Ar = C6H-2,6-(C6H2-2,4,6-iPr3)2-3,5-iPr2 (AriPr8), 4) were synthesized by the reactions of the corresponding bulky terphenyl thiols with mesitylcopper­(I) with elimination of mesitylene. All complexes were characterized by single crystal X-ray diffraction analysis and spectroscopy (NMR, infrared, and UV–vis). The data for 1–3 revealed tetrametallic Cu4 core structures in which two thiolato or two mesityl ligands bridge the metals. Although 1 and 2 feature the expected conventional alternating thiolato and mesityl bridging patterns, 3 has a previously unknown structural arrangement in which the two thiolato ligands are adjacent to each other. Since complex 3 has a more crowding aryl group on the thiolato ligands, the cis arrangement of the ligands in 3 is sterically counterintuitive and is likely due to London dispersion (LD) energy effects. Complex 4 also has an unusual structural pattern in which only a single thiolato ligand is incorporated in the structure probably for steric reasons. It has a planar trapezoidal Cu4 core in which three Cu–Cu edges are bridged by the mesityl groups while the remaining Cu–Cu edge is thiolato ligand bridged. Dispersion connected DFT calculations show that 3 has the highest LD effect stabilization arising from the increased numbers of C–H···H–C interactions of the isopropyl ligand substituents.