Crystal structure of [Li(tmen)2][Li{C(SiMe3)3}2]. A multinuclear magnetic resonance study of tris(trimethylsilyl)methyllithium–tetrahydrofuran(1/2) and –N,N,N′,N′-tetramethylethylenediamine (1/1)(tmen)

Abstract

A single-crystal X-ray study of (Me₃Si)₃CLi·tmen (tmen =N,N,N′,N′-tetramethylethylenediamine) shows that it crystallises with the ionic structure [Li(tmen)₂][Li{C(SiMe₃)₃}₂] but that the anions pack with different orientations from those in crystalline [Li(thf)₄][Li{C(SiMe₃)₃}₂](thf = tetrahydrofuran). The ¹H, ⁷Li, ¹³C and ²⁹Si NMR spectra of (Me₃Si)₃CLi·2thf and (Me₃Si)₃CLi·tmen in thf and toluene, and ⁷Li, ¹³C and ²⁹Si NMR spectra of the solids are described. Spectra obtained from solutions below ca. 25 °C show the presence of ion pairs [Li(thf)₄][Li{C(SiMe₃)₃}₂] or [Li(tmen)₂][Li{C(SiMe₃)₃}₂], together with further species which appear to be different in thf and toluene. Spectra from solutions at higher temperatures show inter-species exchange on the NMR timescale.