Beryllium amides

Because of its toxicity, the number of well-characterized beryllium compounds of all types is much lower than that of the other alkaline earth metals. The largest number of the pubhshed berylhum structures involve oxygen donor ligands, and beryllium amides have been reviewed, at least in part, under the aegis of wider-ranging surveys - of group 2 

Common synthetic routes to beryllium amides, which were summarized in Ref. 1, involve the direct or indirect amination of beryllium hydride, beryllium chloride, a beryllium alkyl or amide precursor. Beryllium amides with bulky substituents are generally synthesized via the trans-metallation of beryllium dichloride with the lithium amides. The reaction of beryllium dichloride with secondary amines in the presence of an alkyllithium represents a less common synthetic route to beryllium amides. The formation ofbery Ilium amides via the reaction of an alkyl beryllium as well as beryllium hydride species with amines is also known.  

Some structural and spectroscopic infonnation for selected beryllium amides and other beryllium species complexed by nitrogen containing ligands is provided in Table 3.1. 

LiAr + BeCh ArBeCl(OEt2) J [ArBe N(SiMe3)2 ] (3.1) 

In this complex the geometry at the beryllium is linear with a very short Be N bond length (1.519(4) A) and a Be C distance of 1.700(4) A. The short Be N interaction is probably due to ionic resonance contributions with a minor contribution from m-bonding between the nitrogen lone pair and the beryllium 2p orbitals. 

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Table 3.1 Selected structural and spectroscopic data for beryllium amides and related complexes...

An important feature of beryllium amide studies since 1980 has been the acquisition of Be NMR data. NMR signals for this nucleus, which has 100% abundance, 1= 3/2 and a receptivity almost two orders of magnitude greater than the nucleus,can be obtained without major difficulties. Some chemical shift data gathered from Refs. 17,18 and 20 are... 

Beryllium complexes, 3, 3 acetylacetone solvolysis, 2, 378 amides, 2, 164 amines, 3, 7 anionic, 3, 10 1,3-diketones... 

Four-coordinate beryllium structures related to amides are exemplified by [Beidad), ... 

Similar reactivity is seen for the alkyls of beryllium,5011 calcium52 and aluminum.53 54 The hydrides of the more electropositive metals will react with amines to liberate hydrogen and give the metal amide. Typically these reactions are carried out in hydrocarbon solvents (equations 2855 and 2915-45). 

Beryllium complexes acetylacetone solvolysis, 378 amides, 164 1,3-diketones... 

The discussion above was limited to alanates, borohydrides, amides, and combinations of these materials. Other hydrides or alternative approaches have also been proposed for storage applications. Zaluska et al. ° studied lightweight lithium-beryllium hydride and showed a reversible hydrogen capacity of over 8 wt%. They also showed that the hydride may be usable down to 150°C. Although these results are rather promising, it is unlikely that any beryllium-containing compound would be considered for vehicular use because of the toxicity of this element, even though the hydride may be quite stable. 

The nitride chemistry of magnesium is remarkably similar to that of beryllium. Olive MgjN, has the antibixbyite structure [104. 105]. and the amide of Mg is formed at elevated pressures [102], The amide is isostrueturul with that of Be discussed above [106]. 

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