Ethylenediamine-bisborane

Ethylenediamine-bisborane (1,2-ethanediamine-bisborane) has been prepared by the reaction of ethylenediamine with diborane 

As a result of the hydridic nature of the hydrogen attached to boron, amine-boranes are interesting and useful reducing agents and have been employed in the reduction of numerous organic carbonyl compounds. They have been utilized in studying the kinetics and mechanism of hydride reactions and are precursors for the synthesis of substituted boranes, borazines, boronium ions, higher boron hydrides, and carboranes. 

The dropping funnel is washed with small portions of tetrahydrofuran to remove all traces of boron trifluoride etherate and then is charged with a solution containing 10.57 g. (0.176 mole) of dry ethylenediamine in 100 ml. of tetrahydrofuran. Commercial ethylenediamine (Eastman 98%) is dried by careful distillation from sodium behind a safety shield in a hood or by the procedure described in reference 11. This solution is added dropwise (about 2-2 hours) and the reaction mixture warmed with stirring to room temperature. 

The suspension is allowed to settle. Solids are collected by filtration through a coarse-fritted-glass funnel under slight nitrogen pressure and are washed with tetrahydrofuran. The combined filtrate and washings are collected in a 1-1. round- 

The product is obtained in nearly quantitative yield. Although it may be useful as a reagent in the form in which it is recovered from solution, this material is usually impure and decomposes more rapidly than the purified compound. 

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Various procedures for the purification of specific amine-boranes have been reported.12 Ethylenediamine-bisborane can be purified conveniently by aqueous extraction to remove water-soluble impurities. The crude product obtained from the tetrahydrofuran solution is ground to a fine powder in a mortar and added in small portions, with stirring, to about 75 ml. of water which has been cooled in an ice-water bath. Foaming may occur during this treatment. The white crystalline solid which does not dissolve is collected by filtration through a coarse-fritted-glass funnel and washed several times with small portions of cold water (about 5°C.). The final wash filtrate should be neutral toward pH paper. The product is dried by... 

Ethylenediamine-bisborane is a white crystalline solid which is quite stable on standing and can be stored at room temperature in a desiccator for several months. It evolves hydrogen slowly on warming and decomposes rapidly at about 90°C. The use of this compound for the reduction of acetone, acrolein, cinnamaldehyde, and acetyl chloride to the corresponding alcohols (isopropyl alcohol, allyl alcohol, cinnamyl alcohol, and ethyl alcohol) has been described.1 Its solubility characteristics and its thermal and hydrolytic stability have been reported.1-4... 

The procedure described for the preparation of ethylenediamine-bisborane is general for the synthesis of amine-boranes and of borane adducts of other electron donors in which elements such as phosphorus and sulfur serve as the donor atom. In addition to the procedure used here for triphenylphosphine-borane, borane adducts of phosphines have been prepared by Analytical reagent grade (Mallinckrodt). 

In ethylenediamine-bisborane, the ethylenediamine acts as a bridge between two BH groups. The B-N-CHg-CH -N-B unit is planar, and the B-N bonds have a typical value of 1.60 A. 

Besides AB, some of its derivatives have also been investigated for hydrogen storage, especially to overcome the previously mentioned problems. The derivatives hydrazine borane (HB) [13], guanidinium borohydride (GBH) [12], ethylenediamine bisborane (EDB) [43], methylguanidinium borohydride (Me-GBH) [44], and different alkyl amine boranes are the most interesting (Fig. 40.3) [45, 14]. Another compound class between molecular and metal hydride storage materials is that of metal amido boranes, which is not discussed in this chapter [46]. 

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