SYNTHESIS, REACTIVITY, AND NMR-STUDIES OF DILITHIATED (E)-1,4-BIS(TRIMETHYLSILYL)BUT-2-ENE AND (E)-1,4-BIS(TRIMETHYLSILYL)-2,3-DIMETHYLBUT-2-ENE

(Z)-1,4-Dilithio-1,4-bis(trimethylsilyl)but-2-ene and 1,4-dilithio-1,4-bis(trimethylsilyl)-2,3-dimethylbut-2-ene adducts of TMEDA (= N,N,N',N'-tetramethylethylenediamine), [{Li(TMEDA)}2{(Me3SiCHCH)2}] (3) and [{Li(TMEDA)}2{(Me3SiCHCMe)2}] (4), respectively, have been prepared by dimetalation of the corresponding (E)-but-2-ene using n-BuLi(TMEDA) in hexane. Assignment of the Z configuration of the dianions with Li atoms bridging the ipso carbons (C1,4) is based on NMR data: magnetically equivalent protons attached to the ipso carbons (C1,4) couple to Li-7 (2JLi-H = ca. 1 Hz) in both compounds, lack of coupling of the protons attached to C2,3 with the lithiums in 3, and NOE enhancements for H-1-Li-7 HOESY experiments. The Z configuration is also consistent with the structures of two isolated silyl derivatives of 3; treatment with ClSiMe3 gives (Z)-1,1,4,4-tetrakis(trimethylsilyl)but-2-ene (5), and with Cl2SiMe2 it yields the (Z<Z)-1,6-disilacyclodeca-3,8-diene [{Me3SiCHC(H) = C(H)CH(SiMe3)SiMe2}2] (6). Compound 3 is a potent reducing agent, affording (EE)-1,4-bis(trimethylsilyl)buta-1,3-diene (7) and metal when treated with HgCl2 (yield of 7 71%) or CaCl2. X-ray diffraction data for 5 revealed a distorted Z double bond, the C-C-C angles at the sp 2 Carbon centers being ''opened up'' to 130.2-degrees (mean): crystals are monoclinic, space group P2(1)/n, with a = 11.595 (4) angstrom, b = 12.205 (1) angstrom, c = 17.569 (6) angstrom, beta = 107.33 (2)-degrees, V = 2373 (1) angstrom 3, and Z = 4.