Lithium Amide and Imide

its structure has proven difficult to fully characterize. The key problem is to identify the location of the hydrogen and lithium positions and the N—H bond orientations. The electronic structure of U2NH was investigated by first-principles calculations [58-60], indicating that the highest occupied states are non-bonding, consisting of N p orbitals. 

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Core structures of some lithium amides and imides (a) (LiTMP)4,... 

The enolates of other carbonyl compounds can be used in mixed aldol reactions. Extensive use has been made of the enolates of esters, thiol esters, amides, and imides, including several that serve as chiral auxiliaries. The methods for formation of these enolates are similar to those for ketones. Lithium, boron, titanium, and tin derivatives have all been widely used. The silyl ethers of ester enolates, which are called silyl ketene acetals, show reactivity that is analogous to silyl enol ethers and are covalent equivalents of ester enolates. The silyl thioketene acetal derivatives of thiol esters are also useful. The reactions of these enolate equivalents are discussed in Section 2.1.4. 

Lithium amides and lithium imides (iminolithiums) (R2C=NLi) have also been used to prepare amides and imides of other metals and... 

Amide and imide enolates. Scheme 5.31 illustrates several examples of asymmetric Michael additions of chiral amide and imide enolates. Yamaguchi [163] investigated the addition of amide lithium enolates to -ethyl crotonate, but found no consistent topicity trend for achiral amides. The three chiral amides tested are illustrated in Scheme 5.31a-c. The highest diastereoselectivity found was with the C2-symmetric amide shown in Scheme 5.3Ic. Evans s imides, as their titanium enolates, afforded the results shown in Scheme 5.31d and e [164,165]. The yields and selectivities for the reaction with acrylates and vinyl ketones are excellent, but the reaction is limited to P-unsubstituted Michael acceptors P-substituted esters and nitriles do not react, and 3-substituted enones add with no selectivity [165]. 

Amides and Imides (—NH2, = NH) The thermal hydrogen desorption from lithium amide (LiNH2) was investigated by Chen et al. [41, 42]. The thermal desorption of pure lithium amide mainly evolves NH3 at elevated... 

Lithium Amide. Lithium amide [7782-89-0], LiNH2, is produced from the reaction of anhydrous ammonia and lithium hydride. The compound can also be prepared by the removal of ammonia from solutions of lithium metal in the presence of catalysts (54). Lithium amide starts to decompose at 320°C and melts at 375°C. Decomposition of the amide above 400°C results first in lithium imide, Li2NH, and eventually in lithium nitride, Li N. Lithium amide is used in the production of antioxidants (qv) and antihistamines (see HiSTAMlNE AND HISTAMINE ANTAGONISTS). 

The reactivity of lithium enolates has been explored in a theoretical study of the isomers of C2H30Li, such as the lithium enolate, the acyl lithium, and the a-lithio enol. Imides containing a chiral 2-oxazolidine have been employed for enantioselective protonation of prochiral enolates.A degree of kinetic control of the product E/Z-enolate ratio has been reported for the lithiation of 3,3-diphenylpropiomesitylene, using lithium amides/alkyls. " °... 

Metal amides can be added to ordinary nitriles e.g. lithium, sodium or magnesium amides), thus forming amide imide salts, which on addition of water or alcohol afford amidines. Some recent results demonstrate the wide applicability of the method, e.g. from metal amides and trialkoxyacetonitriles, tri-alkoxyacetamidines (319 Scheme 52) were prepared and from lithium imides and nitriles A -alkylide-neamidines (320) could be synthesized. 

Lithium also forms an imide, Li2(NH) as well as a beige nitride-hydride. Li4NH [39], It was assumed that the nitride- hydride formed with an antifluorite superstructure in a large tetragonal cell however, our neutron diffraction studies [40] have not confirmed this behavior. It is formed from the nitride and hydride directly at 500 C or the decomposition of the amide under vacuum. The imide also forms from decomposition of the amide and has the antifluorite structure [41] with a rotationally disordered NH2 group. 

Chiral amides (222) and (223) and imides (224) and (225) have also been studied as reagents for asymmetric aldol reactions. These reagents show excellent diastereofacial preferences as their boron and zirconium enolates, but generally show poor selectivity as their lithium enolates. The reader is referred to other chapters in this volume for a discussion of these and related reagents. 

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