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

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.