Lithium magnesium alanate

M. Mamatha, B. Bogdanoviq M. Felderhoff, A. Pommerin, W. Schmidt, F. Schiith, C. Weidenthaler, Mechanochemical preparation and investigation of properties of magnesium, calcium and lithium-magnesium alanates , J. Alloys Compd. 407 (2006) 78-86. 

One attractive feature of alanates is that lithium and sodium salts are readily available commercially. Magnesium alanate can be readily prepared with sodium alanate and magnesium hydride via a metathesis reaction. The mixed metal alanate, Na2LiAlH6, is prepared through ball milling of sodium hydride, lithium hydride, and sodium alanate. Potassium alanate can be prepared by the direct synthesis of potassium hydride and aluminum under high temperature and pressure." ... 

To a solution of 0.24 mol of lithium alanate in 500 ml of diethyl ether was added 0.20 mol of the acetylenic alcohol (note 1) at a rate such that gentle refluxing of the diethyl ether was maintained. After the addition the mixture was warmed under reflux for an additional 1 h. It was then cooled to 0 C and subsequently poured on to 400 g of finely crushed ice. After the remaining ice had melted the layers were separated (note 2). The aqueous layer was extracted several times with diethyl ether. The combined ethereal solutions were dried over magnesium sulfate and subsequently concentrated in a water-pump vacuum. Distillation of the residue through... 

Lithium aluminum hydride and alanes are frequently used for the preparation of hydrides of other metals. Diethylmagnesium is converted to magnesium hydride [777], trialkylchlorosilanes are transformed to trialkylsilanes... 

High yields of amines have also been obtained by reduction of amides with an excess of magnesium aluminum hydride (yield 100%) [577], with lithium trimethoxyaluminohydride at 25° (yield 83%) [94] with sodium bis(2-methoxy-ethoxy)aluminum hydride at 80° (yield 84.5%) [544], with alane in tetra-hydrofuran at 0-25° (isolated yields 46-93%) [994, 1117], with sodium boro-hydride and triethoxyoxonium fluoroborates at room temperature (yields 81-94%) [1121], with sodium borohydride in the presence of acetic or trifluoroacetic acid on refluxing (yields 20-92.5%) [1118], with borane in tetrahydrofuran on refluxing (isolated yields 79-84%) [1119], with borane-dimethyl sulflde complex (5 mol) in tetrahydrofuran on refluxing (isolated yields 37-89%) [1064], and by electrolysis in dilute sulfuric acid at 5° using a lead cathode (yields 63-76%) [1120]. 

Alanates and amides have also been studied. First-principle calculations suggest calcium alanate has many potentially attractive combinations, but calcium alanate itself is likely to be too unstable (Alapati et al., 2007a). There is also a lot of interest in lithium hydride with lithium amide (Chen et al, 2002) and with magnesium amide (Leng et al., 2004), but these are discussed in detail in Chapter 15. 

The reactivity of the aluminum-carbon bonds is greatly reduced in the 1 1 adducts, and this may be utilized in preparing particularly labile organoaluminum compounds which cannot be isolated in the free form. Thus tri-tert-alkyl alanes, such as tri-terf-butylalane, may be prepared as etherates from tertiary butyl lithium in diethylether (207) or from the corresponding magnesium tertiary alkyls (157, 159) ... 

To a solution of 8 g of lithium alanate in 250 ml of diethyl ether was added in 15 m1n 24 g (0.3 mol) of 2-penten-4-yn-l-ol (111, Exp. 57). The diethyl ether began to reflux and a rubber-like greyish precipitate was formed. After heating for 1 h under reflux the flask was placed in an ice + ice-water bath and water (150 ml) was added dropwise with vigorous stirring. After this hydrolysis procedure the ethereal solution was decanted and the aqueous jelly layer was extracted ten times with diethyl ether. The ethereal extracts were dried (without washing) over magnesium sulfate and subsequently concentrated in a water-pump vacuum. 

---