SYNTHESIS AND X-RAY CRYSTAL-STRUCTURE OF [LI2CU2(CH2SIME3)4(SME2)2]INFINITY - THE 1ST DETAILED STRUCTURAL CHARACTERIZATION OF A LITHIUM DIALKYLCUPRATE AGGREGATE

The use of SMe2 (dimethyl sulfide) as both ligand and solvent has allowed the first X-ray structural characterization of a lithium alkylcuprate aggregate. The title compound [Li2Cu2{CH2SiMe3)4(SMe2)2]„ (1) was synthesized by the reaction of 2 equiv of LiCH2SiMe3 with CuBr in SMe2. Its structure consists of infinite chains of the dimeric units Li2Cu2(CH2SiMe3)4 linked by weakly bridging SMe2 ligands that bind to the lithium centers. The Li2Cu2 array is almost planar, and the α-carbons of the alkyl groups reside in alternating positions approximately 1.3 Â above and below the metal plane. The Li-S distances, 2.65-2.71 Λ, are long, and the Li-C bonds, ~2.2 Â, are short. Thus, the Li atoms are relatively strongly bonded to the α-carbons of the alkyl group. The Cu-C distances are ~ 1.956 A, which is close to the values in arylcuprates. The structure of 1 is significantly different, in certain details, from that predicted for LUCujN^ on the basis of spectroscopy and theoretical calculations. © 1990, American Chemical Society. All rights reserved.