Reactions of MAlH4 (M = Li, Na) with primary amines — Synthetic and structural studies of alkali metal tetrakis(amido)aluminates and related dinuclear complexes

Abstract

The reactions of MAlH4 (M = Li, Na) with primary amines NH2R (R = t-Bu, i-Pr, p-tolyl) in a 1:4 molar ratio in THF produce the tetrakis(amido)aluminates, [M(THF)n][Al(NHR)4], in yields of 46%–82% together with secondary products. The extent of solvation of the alkali-metal cation varies from none (n = 0) for M[Al(NH-i-Pr)4] (2b, M = Li; 3b, M = Na) to n = 4 in the complex [Li(THF)4][Al(NH-p-tolyl)4] (2c), which exists as a solvent-separated ion pair. The complexes 2b, 3b, and [Na(THF)][Al(NH-p-tolyl)4]∞ (3c) all exhibit one-dimensional polymeric structures in which the bis-N,N′-chelating tetrakis(amido)aluminate anions are bridged by four- (2b, 3b) and five-coordinate (3c) metal ions, respectively. The structures of two of the secondary products, {[Na(THF)2][(NH-t-Bu)Al(H)(µ-N-t-Bu)]}2 (4) and {[Na(THF)3][(NH-p-tolyl)2Al(µ-N-p-tolyl)]}2 (5), were established by X-ray crystallography. Complex 4 is a dimer of the [HAl(NH-t-Bu)(N-t-Bu)]– anion, which forms a central Al2N2 ring with each monoanion N,N′-chelated to a [Na(THF)2]+ cation. Complex 5 is a dimer of the [Al(NR)(NHR)2]– (R = p-tolyl) anion in which the bridging p-tolyl groups are coordinated in an N-monodentate fashion to the trisolvated [Na(THF)3]+ cations. Key words: aluminohydrides, alkali metals, primary amines, tetrakis(amido)aluminates, structures.