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

The direct reactions of the large terphenyl thiols HSAriPr4 (Ar-iPr4 = -C6H3-2,6-(C6H3-2,6-iPr(2))(2)) and HSAriPr6 (Ar-iPr6 = -C6H3-2,6-(C6H2-2,4,6-iPr(3))(2)) with stoichiometric amounts of mesitylcopper(I) in THE at ca. 80 degrees 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 A 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 Cu-A 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 {LiSAriPr6}(2) (3) and {LiSAriPr6}(2) (4) which were synthesized directly from thiols despite the very similar effective ionic radii of the Li+ (0.59 angstrom) and Cu+ (0.60 angstrom) ions, the Li--Li structures display very much longer (by more than ca. 0.5 A) separations than the corresponding Cu--Cu distances in 1 and 2, which may be due to weaker dispersion interactions.