Amides hydride

Scheme47 DIBAH-mediated [amide] -[hydride] transformation in nnsa-lanthan-idocene(III) complexes (Ln = Y, Ho) [213]...

Figure 10 Cyclopentadienyl-amide hydride complex of yttriiun...

Figure 6.15 Chemical reactions at the interfaces of amide/hydride, amide/imide, and imide/hydride and mass transport through the imide layer [113],...

The reaction yielded a reversible hydrogen capacity of 6.5 wt%. If the imide were subsequently decomposed, the overall hydrogen capacity of the amide-hydride pair would be 11.5 wt%. As with other systems, however, this total capacity has not been achieved reversibly. Furthermore, the formation enthalpy and hydrogen transport kinetics of this system require high temperatures ( 350°C) for hydrogen release at reasonable rates. Some improvement in hydrogen release kinetics was achieved by incorporating Ti catalysts. ... 

This method consists in the generation of the enolato hgand by deprotonation of the corresponding carbonyl compound RC(0)CHR R" in the presence of a metal (M) salt or complex. However, frequently the deprotonating agent is a compound of a different metal, M X (M = alkali, alkaline-earth, T1(I), etc., X = amide, hydride, acetate, etc.). In this case, the synthesis of the desired complex is a one-pot, two-step process consisting of [M ]—OC(=CR R")R formation followed by transmetalation of the enolato ligand from [M ] to [M]. 

In the presence of MgH2 however, and by analogy with the Li-N-H and Ca-N-H systems, the decomposition should evolve H2 in place of NH3 presumably, also by analogy, via the rapid reaction of the hydride with evolved NH3. Hence by changing the ratio of amide hydride, two outcomes are potentially possible (Eqs 16.20 and 16.21) ... 

Two independent studies rapidly followed considering the alternative pathway to mixed imides in the Li-Mg-N-H system, namely combining magnesium amide with lithium hydride [84, 85]. The two studies differed in the ratios of starting materials considered. The former took the 1 2 ratio of amide hydride and by analogy to Eq. (16.22) sought to liberate hydrogen as a by-product of mixed imide formation, viz. Eq. (16.23) (hereafter referred to as the 1 2 reaction based on the Mg(NH2)2 LiH ratio) ... 

The ligands R can be exclusively halide, amide, hydride, or smart leaving groups like trimethylsilyl (TMS) or trimethylstannyl, or combinations of them. Some, but never all, of the sites R may be occupied by saturated or unsaturated organic substituents. In the case of boron hydrides, the Lewis base (D) adducts are preferred because they are much easier to handle than the pure boranes. 

If only a single electron-withdrawing substituent is present, as with simple ketones, esters, and nitriles, the formation of alkyl derivatives in high yield requires careful control of reaction conditions. Use of bases that are strong enough to effect only partial conversion of the substrate to its anion can result in aldol-condensation reactions with ketones and Claisen condensations with esters (see Chapter 2 for discussion of these reactions). This problem can be partially avoided by use of very strong bases such as the amide, hydride, or triphenylmethyl anions. 

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