σ-Carbon versus π-Arene Interactions in the Solid-State Structures of Trimeric and Dimeric Copper Aryls (CuAr)n (n = 3, Ar = 2,6-Ph2C6H3; n = 2, Ar = 2,6-Mes2C6H3)

Reaction of LiC 6 H 3 Ph 2 -2,6 or LiC 6 H 3 Mes 2 -2,6 with CuO t -Bu in pentane or toluene yields the unsolvated copper aryls (CuC 6 H 3 Ph 2 -2,6) 3 ( 2 ) and (CuC 6 H 3 Mes 2 -2,6) 2 ( 3 ). Addition of another equivalent of lithium aryl to 3 affords the lithium cuprate LiCu(C 6 H 3 Mes 2 -2,6) 2 ( 4 ). The new compounds 2 − 4 were characterized by 1 H NMR, 13 C NMR, IR spectroscopy, mass spectrometry, and X-ray crystallography. The X-ray structure shows 2 to be trimeric in the solid state. The bridging terphenyl ligands exhibit two different coordination modes. Two of them connect two copper atoms via their ipso C 6 H 3 carbons, while the third bridges two copper centers by either a σ-C ( ipso C 6 H 3 ) or a π-arene ( ipso / ortho phenyl) interaction. A dimeric unit is observed in the solid-state structure of 3, in which the two aryl groups are linked by two bridging coppers. The copper atoms mainly interact with the ipso carbons of the C 6 H 3 group. The quasi-linear coordination is completed by two ipso and ortho carbons of a mesityl group. Molecular weight determinations of the copper aryls 2 and 3 by cryoscopy in benzene solution show an equilibrium between monomers and dimers. Compound 4 is the first example of a structurally characterized, monomeric, nonsolvated lithium cuprate. It crystallizes with two independent molecules, showing C−Cu−C angles of 171.1° and 173.8°, respectively. The lithium ions are accommodated between two adjacent mesityl groups of the terphenyl ligands.