Syntheses and crystal structures of some lithium di- and tri-(thiolato)[tris(trimethylsilyl)methyl]aluminates

The first organodi- and organotri-(thiolato)aluminates have been prepared and structurally characterised. They have been obtained by the reactions of [Li(thf)(2){AlH3[C(SiMe3)(3)]}](2) 1 (thf = tetrahydrofuran) with disulfides R2S2 (R = Me, Et or Ph) or thiols RSH (R = Pr-i, Bu-t or Ph). The structure of the methyl compound [Li(thf)(2){Al[C(SiMe3)(3)](SMe)(3)}] 2 has been determined by X-ray crystallography and shown to comprise lithium organotri(thiolato)aluminates each containing a folded four-membered LiS2Al ring. NMR spectroscopy indicates that the Et, Pr-i and Ph derivatives have similar structures in solution. Treatment of compound 1 with a three-fold excess of (BuSH)-S-t led to the replacement of only two of the available Al-H bonds and formation of [Li(thf){AlH[C(SiMe3)(3)](SBut)(2)}] 6, which contains an almost planar four-membered LiS2Al ring. The derivatives [Li(tmen)(2)][Al{C(SiMe3)(3)}(SR)(3)] (R= Bu-t or Ph) have been made by treatment of [Li(tmen)(2)][AlH3{C(SiMe3)(3)}] 9 (tmen = N,N,N',N'-tetramethylethane-1,2-diamine) with RSH, and the Bu-t derivative has been shown to crystallise in a lattice containing separated [Li(tmen)(2)] cations and [Al{C(SiMe3)(3)}(SBut)(3)] anions.