Dimeric Copper and Lithium Thiolates: Comparison of Copper Thiolates with Their Lithium Congeners

The direct reactions of the large terphenyl thiols HSAriPr4 (AriPr4= −C6H3-2,6-(C6H3-2,6-iPr2)2) and HSAriPr6 (AriPr6= −C6H3-2,6-(C6H2-2,4,6-iPr3)2) with stoichiometric amounts of mesitylcopper­(I) in THF at ca. 80 °C afforded the first well-characterized dimeric copper thiolato species {CuSAriPr4}2 (1) and {CuSAriPr6}2 (2) with elimination of mesitylene. The complexes 1 and 2 were characterized by NMR and electronic spectroscopy as well as by X-ray crystallography. They have dimeric Cu2S2 core structures in which the two copper atoms are bridged by the sulfurs from the thiolato ligands and feature short Cu--Cu distances near 2.4 Å as well as a weak copper-flanking aryl ring interaction from a terphenyl substituent. The structures of the planar Cu2S2 cores bear a resemblance to the CuA site in nitrous oxide reductase in which two cysteines also bridge two copper atoms. The related dimeric Li2S2 structural motif was also observed in the lithium congeners {LiSAriPr4}2 (3) and {LiSAriPr6}2 (4) which were synthesized directly from the thiols and n-BuLi in hexanes. However, despite the very similar effective ionic radii of the Li+ (0.59 Å) and Cu+ (0.60 Å) ions, the Li--Li structures display very much longer (by more than ca. 0.5 Å) separations than the corresponding Cu--Cu distances in 1 and 2, which may be due to weaker dispersion interactions.