X-ray crystallographic studies and comparative reactivity studies of a sodium diisopropylamide (NDA) complex and related hindered amides

Article abstract of DOI:10.1016/0022-328X(96)06203-1

Two related sodium amide complexes derived from secondary amines with bulky organic substituents have been synthesised and crystallographically characterised. Both [(ⁱPr)₂NNa(TMEDA)]₂ and [Cy(ⁱPr)NNa(TMEDA)]₂ adopt dimeric crystal structures with a central, planar (nitrogen-metal)₂ azametallocycle, a now familiar feature in both lithium amide and sodium amide chemistry. TMEDA ligands chelate in their usual bidentate manner making the Na⁺ cations four-coordinate with a distorted tetrahedral geometry. In the latter complex, the amido substituents are disposed in a trans conformation with respect to the (NNa)₂ ring plane. The deprotonating ability of the former complex has been tested against that of the parent amide [(ⁱPr)₂NNa]_∞ and the lithium congener [(ⁱPr)₂NLi]∞ (LDA) in a series of simple organic reactions: selective enolate formation from 2-octanone and 2-methylcyclohexanone; synthesis of diphenylacetic acid via diphenylmethane. In general, the performance of the sodium reagents compares favourably with that of the lithium reagent.