Unveiling the Structural Complexity of Lithium Organozinc Alkoxo Clusters and their Applications to Enantioselective Michael Addition Reactions

Abstract

We report three novel lithium zincate alkoxo clusters, which can be accessed through a convenient co-complexation reaction of the corresponding dialkylzinc derivatives with lithium alkoxides of the formula [LiO(CH₂)₂N(CH₃)₂], or via a deprotonation process mediated by the higher-order zincate Li₂ZnEt₄ and dimethylethanolamine. These complexes have been isolated as colourless crystalline solids and characterised by multinuclear magnetic resonance spectroscopy, elemental and single-crystal X-ray diffraction analysis. XRD analysis of the crystal structures, combined with ¹H DOSY NMR experiments, was crucial for understanding the chemistry behind these complexes. Furthermore, complexes obtained by mixing ZnEt₂ with a chiral nonracemic lithium alkoxide generated from (1R,2S)-N-methylephedrine have been explored in promoting an enantioselective Michael addition reaction towards trans-β-nitrostyrene, with the corresponding nitroalkane isolated in up to 37.3 % enantiomeric excess.