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Keywords:

  • Lithium;
  • Chiral metal amides

Abstract

Monolithiation of the chiral amine (S)-N-(α-methylbenzyl)allylamine, in the presence of the strong Lewis donor solvent hexamethylphoshoramide (HMPA), results in pale yellow crystals which have been crystallographically analysed revealing the structure of the complex to be an asymmetriccisoid dimer {(S)-α-[PhC(H)CH3](CH2CH=CH2)NLi·HMPA}2. Variable-temperature NMR studies show this complex can undergo a thermally induced rearrangement to a 1-azaallyl complex at ca. 90 °C. Attempted dilithiation of the chiral amine at the N and vinylic C centres with nBuLi and HMPA results in competitive reduction of HMPA to give crystals of the lithium dimethylamidophosphite, structurally authenticated as the hexamer [(Me2N)2POLi]6, in which the Li cation is bonded preferentially to the O centre and not P. The effect is a reduction in the oxidation state of the P centre from (V) to (III), which is supported by ab initio calculations showing the crystal structure to represent the most thermodynamically stable of the possible isomers. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)