ISOLATION AND 1ST STRUCTURAL CHARACTERIZATION OF DIMETHYL SULFIDE SOLVATES OF PHENYLLITHIUM, PHENYLCOPPER, AND LOWER AND HIGHER-ORDER LITHIUM PHENYLCUPRATE REAGENTS

The use of dimethyl sulfide as a solvent for organocopper reagents has allowed the first X-ray structure determinations of crystalline materials isolated from the addition of phenyllithium, in various ratios, to cuprous bromide in neat dimethyl sulfide. Upon removal of the insoluble lithium bromide, solutions of the 1:1 mixture yield crystals of [Cu4Ph4(SMe2)2] (lilts structure has a rhombus of four coppers that are edge-bridged by phenyl groups perpendicular to the Cu4 plane and displays both long and short Cu…Cu diagonal distances of 4.101 (2) and 2.717 (2) Å, respectively. Two equivalents of LiPh with CuBr affords the species [Li2Cu2Ph4(SMe2)3] (2), an aggregate of two [CuPh2]- moieties bridged by two Li+ ions which are solvated by one and two SMe2 groups. Treatment of CuBr with 3 equiv of LiPh produces the higher order cuprate [Li3(CuPh2)-(CuPh3)(SMe2)4] (3). The first X-ray structural determination of such a species shows it to be an aggregate of CuPh2- and CuPh32- moieties that are bridged by three Li+ ions and solvated by four SMe2 groups. A 10% excess over 3 equiv (3.3 equiv of LiPh per CuBr) does not give the all-trigonal higher order cuprate. Instead the larger aggregate, [Li5(CuPh2)3(CuPh3)(SMe2)4] (4), is obtained. The structure of the phenyllithium precursor [Li4Ph4(SMe2)4] (5) was also determined and found to be tetrameric, with one set of alternating corners of a cube occupied by Li(SMe2) and the other set of corners occupied by triply-bridging phenyls. It is the first structure of an organolithium thioether solvate complex that was crystallized from a thioether. The results demonstrate that it is possible to isolate higher order cuprates as crystalline materials from Me2S solutions. Furthermore, the X-ray data are consistent with previously reported 13C NMR solution studies that indicated the presence of 1, 2, 3, and 5 in solution. In addition, structural relationships between LiPh, CuPh, LiCuPh2, and the higher order phenyl cuprates have now been established which show that the ions [CuPh2]- and [CuPh3]2- are the dominant structural components in the cuprates when crystallized from Me2S. A possible explanation for the lack of formation of certain higher order cuprates in conventional ether solvents is also provided. © 1990, American Chemical Society. All rights reserved.