Ammonia-borane

Synthesis. An efficient, convenient synthesis for the preparation of ammonia borane [13774-81 -7] the inorganic analogue of ethane, is shown in equation 1 where THF is tetrahydrofuran (6). 

The synthesis of borazine (Fig. 1) was first described in 1926 by Stock and Pohland.12 More recently, Wideman and Sneddon reported interesting three one-step synthetic procedures using various starting compounds including 2,4,6-trichloroborazine, metal borohydrides, and ammonia-borane.13 The B N bond is isoelectronic with the C C bond, which explains why borazine is often presented as the inorganic analog of benzene, that is, borazine has almost the same colligative properties as benzene. 

Zhou, X., et ah, Deposition ofFe-Ni nanoparticles on polyethyleneimine-decoratedgraphene oxide and application in catalytic dehydrogenation of ammonia borane. Journal of Materials Chemistry, 2012. 22(27) p. 13506-13516. 

Figure 11.1 Enzymatic deracemization of racemic amines via a two-step, one-pot process utilizing an enantioselective amine oxidase in combination with ammonia-borane.

Whole wet cells ( 440 mg) expressing the MAO-N-D5 variant enzyme were suspended in 0.1 M potassium phosphate buffer pH 7.6 (2.46 mL). Racemic crispine A (6.0 mg, 0.03 mmol) was added to this suspension followed by ammonia-borane (3.5 mg, 0.11 mmol). The vial was sealed with the stopper and the mixture was incubated at 30 °C, 250 rpm and samples (0.5 mL) taken periodically for analysis. 

Chemical hydrogen storage-where hydrogen is stored in a chemical compound and released via a reversible chemical reaction-represents a promising strategy [36]. Ammonia borane (H3NBH3) and related aminoborane compounds have... 

The result of theoretical investigations have suggested that cleavage of a B—H bond occurs to initiate ammonia borane dehydrogenation [38]. Alternatively, the oxidative N—H addition of ammonia to the dehydrogenated intermediate C may constitute a feasible reaction pathway due, in particular, to the fact that ammonia and aniline oxidative addition to la and related iridium-PCP systems has been reported experimentally [39]. 

Scheme 2.31 Deracemization of amines via combined use of an enantioselective amine oxidase and ammonia borane.

Borazine, B3N3H6, was first prepared by thermolysis of the diborane ammonia adduct [(BH2)(NH3)2] [BH4] . More convenient procedures for the laboratory preparation of this important ring system in multigram quantities involve either (a) the decomposition of ammonia- borane [eqn (9.1)] or (b) the reaction between ammonium sulfate and sodium borohydride [eqn (9.2)]. The latter method provides a convenient and economical synthesis of borazine. 

The formation of individual cycloborazanes can be achieved, in some cases, by transition metal-catalysed dehydrocoupling reactions. By using this strategy, secondary amine-boranes are converted to the four-membered ring (H2BNMe2)2 under mild conditions, whereas primary amine-boranes produce borazines. The cyclic pentamer is obtained as the exclusive product from ammonia-borane adduct H3B NH3 employing an iridium(fll) catalyst [see eqn (2.13) in Section 2.3)]. 

AMMONIA-BORANE p-Bis(cyanotri-hydroborato)tctrakis(triphenylphos-... 

Borazine can be prepared in a variety of ways, including the reaction of NH3 with BC13 to form B,B, B"-trichloroborazine, C13B3N3H3, which is then treated with NaBHi to yield B3H3H6. However, these and other literature methods are hampered by limitations of scale and other problems. Improved routes that utilize reactions of ammonia-borane (H3N BH3) at 140-160°C or alternatively, (NH4)2S04 and NaBIL at 120-140°C, to afford very pure borazine on a multigram scale have been reported recently.25... 

Ammonia Borane and Related Compounds as Hydrogen Source Materials... 

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