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

Abstract

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]}]₂1 (thf = tetrahydrofuran) with disulfides R₂S₂ (R = Me, Et or Ph) or thiols RSH (R = Prⁱ, 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, Prⁱ and Ph derivatives have similar structures in solution. Treatment of compound 1 with a three-fold excess of Bu^tSH led to the replacement of only two of the available Al–H bonds and formation of [Li(thf){AlH[C(SiMe₃)₃](SBu^t)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}(SBu^t)₃] anions.