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dem verehrten Kollegen und Freund, zum 60. Geburtstag gewidmet (12.VI.85)On the Interaction between Lithium Enolates and Secondary Amines in Solution and in the Crystal When lithium derivatives generated by lithium diisopropylamide (LDA) are quenched with a D+ source (large excess of ROD), there is frequently only partial deuterium incorporation (non-stoichiometric effect, Scheme I ) . Experiments with tert-butyl 2-methylpropionate (1) and its deuterated derivative (2-D)-1 and LDA indicate that the lack of deuteration is not caused by an isotope effect (Scheme 2). A H-bonded complex between the amine (R,NH) and the Li-derivative was envisioned as being responsible for the observed effects. Some crystalline Li-enolate solvates with secondary amines were isolated, and gave rise to only partially deuterated products upon quenching with AcOD/CD30D ( Table I ) . Enolates containing the Li-chelating diamine N,N,N -trimethylethylenediamine (TriMEDA) turned out to be especially suitable for the isolation of single crystals. Thus, two X-ray crystal-structure analyses were undertaken to obtain detailed information about the geometry and bonding in such complexes. The structures of the dimeric N,N-dimethyl-propionaniide lithium (2)-enolate ([2 (2)-4.2 TriMEDA]; R value 0,049, see Eqn. 2, Figs. 2.4 and 5 ) and of the dimeric pinacoloue lithiumenolate ([2 6.2 TriMEDA]; R value 0,082, see Eqn.3 and Figs.3, and 6) were determined. In both centrosymmetric dimeric structures there is a Li-0-Li-0 four-membered ring anda H-bridge between TriMEDA and the enolate moiety. In the case of the amide enolate (2)-4 .TriMEDA the bridge points from the amine N-atom to the pyramidalized, enatnine-type N-atom of