Solutions of Lithium Tetrahydrido Aluminates in Ethers: a 7Li and 27Al NMR Study

Abstract

Solutions of LiAlH4 in tetrahydrofuran (THF), glycoldimethylether (monoglyme), diglycoldimethylether (diglyme) and triglycoldimethylether (triglyme) as well as solutions of LiAlH4/THF in toluene have been investigated by 7Li and 27Al NMR. It was found that δ27Al is nearly independent of the solvent as is 1J(AlH). However, the line width of the 27A1 NMR signal shows strong solvent influences and, in addition, concentration and temperature dependence. Intermolecular hydride exchange becomes rapid in solutions of monoglyme and triglyme at room temperature. This can also be shown by the H/D exchange between LiAlH4 and LiAlD4. δ7Li data indicate that Li is hexacoordinated in the series of glycoldimethylethers, and LiAlH4 in diglyme seems to be the system in which the AlH4 moiety is least affected by ion pair or triple ion formation.