Substituted Ammonia Boranes

A strong influence of crystallinity, particle size, and thus of the preparation conditions on its activity to vards the hydrolysis of AB vas also found by others [92, 118, 

To a certain degree the presented catalytic results can be expected to be applicable to AB-related compounds. Yoon and Sneddon have demonstrated that the hydrolysis of ammonia triborane NH3B3H7 can be performed vith concentrations up to 22.7 wt.% [121] using a 5 wt.% Rh catalyst at 21 °C, achieving a hydrogen release of 6.1 wt.% solution based. 

The number of substituted AB-compounds with one or more hydrogen atoms replaced is legion. A large number are well described in the Gmelin series, where 

Since the material obtained by ball-milling is X-ray amorphous, the identification as BH3NH2Li is not straightforward. It was eventually carried out by by Xiong et al. by applying high resolution powder X-ray diffraction analysis [125]. 

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S Ammonia Borane and Related Compounds as Hydrogen Source Materials Table 8.5 Hydrogen release from substituted AB materials. 

Reaction scope Although there have been extensive investigations into the stoichiometric reactions of group 2 complexes with ammonia-borane [119, 147-153], secondary amine-boranes, and primary amine-boranes and their thermal decomposition products, only a handful of catalytic reactions have been reported. The reaction products depend on the substitution of the amine-borane. For example. Harder and coworkers have reported that the sterically demanding primary amine-borane ArNH2 BH3 (Ar = 2,6-di-/so-propylphenyl) reacts to... 

SCHEME 18.30 Proposed mechanism of the n-BuLi catalyzed dehydrocoupling of tris(hydridosilyl-ethylene)boranes and ammonia. (1) deprotonation with formation of an amide, (2) substitution of silicon-bonded hydride with amide, (3) polymerization through condensation. 

Well-authenticated boron hydrides are listed in Table I. Characterization of these hydrides does not preclude the isolation of others (33). Properties known at present to be common to all boranes include thermal instability susceptibility to hydrolysis, to alcoholysis, and to oxidation toxicity ability to react with ammonia and with many electron-pair donor molecules [for example, (CH3)3N] and a tendency to undergo substitution of their hydrogen atoms by halogen or alkyl groups. 

A 5 -P-borane-substituted thymidine monophosphate (68) and triphosphate (see Section 2) have been prepared from the boranophosphoramidate (69) which was obtained by reacting the thymidine 5 -(J-cyanoethylphosphoramidite with borane-diisopropylethylamine complex followed by treatment with ammonia. Acid hydrolysis of (69) gave the thymidine monophosphate derivative (68).The compound shows similar stability to normal nucleoside monophosphates, hydrolysis proceeding by P-0 rather than P-B cleavage. Acid phosphatase hydrolysed (68) to thymidine whilst the analogue was not a substrate for alkaline phosphatase. 

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