1769-74-0Relevant articles and documents
METHODS FOR SYNTHESIZING AMMONIA BORANE
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Page/Page column 4; 11; 7, (2008/06/13)
Methods of synthesizing ammonia borane are provided. The methods comprise reacting at least one amine borane with ammonia such that ammonia borane is produced. Ammonia borane has a chemical formula Of NH3-BH3 and provides a good source of storage hydrogen making it useful in a variety of applications including a potential hydrogen source for fuel cells. The methods can further comprise separating the ammonia borane from the other products of the reaction. Exemplary methods can produce ammonia borane having purity greater than about 90 percent. In further examples, the methods can produce ammonia borane having purity greater than about 95 percent or greater than about 99 percent.
Disproportionation of cationic zirconium complexes: A possible pathway to the deactivation of catalytic cationic systems
Choukroun, Robert,Douziech, Bénédicte,Donnadieu, Bruno
, p. 5517 - 5521 (2008/10/08)
Protonolysis of the zirconium borohydride [(C5H4R)2Zr(BH4)2] (R = H, Me, SiMe3) with NHMe2PhBPh4 in THF leads to the corresponding cationic zirconium complex [(C5H4R)2Zr-(BH4)(THF)]BPh 4, and the structure of [(C5H4Me)2Zr(BH4)(THF)]BPh 4 was determined. In the presence of phosphine, PMe2Ph, the formation of the cationic hydride [(C5H4R)2ZrH-(PMe2Ph) 2]BPh4 is observed by 1H and 31P NMR followed by a disproportionation and a redox reaction with [BPh4]-, giving the neutral [(C5H4R)2ZrH(μ-H)]2 and the cationic ZrIII species [(C5H4R)2Zr(PMe2Ph) 2]BPh4 characterized by EPR spectroscopy and suggesting a probable pathway in the deactivation of cationic catalyst systems.
Molecular addition compounds. 9. Effect of structure on the reactivities of representative borane-amine complexes in typical reactions such as hydrolysis, hydroboration, and reduction
Brown, Herbert C.,Murray, Leo T.
, p. 2746 - 2753 (2008/10/08)
A number of borane-amine complexes with widely different structural features in the amine portion was prepared and their reactivities toward typical B-H reactions, such as hydrolysis, hydroboration of 1-octene, and reduction of cyclohexanone, were studied. BH3-amine complexes containing an N-phenyl group are hydrolyzed by neutral hydroxylic solvents, while others require a strong acid medium for the hydrolysis. In hydroboration, BH3-N-phenylamine complexes react rapidly with 1-octene in THF at 25°C, while all other types require refluxing THF or toluene for reaction. Again, BH3-N-phenylamine complexes reduce cyclohexanone in THF at 25°C at reasonable rates, while others require acetic acid solvent or mineral or Lewis acids to achieve the desired reduction. Thus, among such borane-amine addition compounds, the BH3-N-phenylamines emerge as unique hydroborating and reducing agents. The results of the present study provide insights into the mechanisms of the hydroboration and reduction reactions. The rates of hydroboration of alkenes with BH3-amine complexes are inversely related to the stability of the adduct, arguing for a prior dissociation of the adduct, followed by the reaction of BH3 with the alkene. The reduction of cyclohexanone with BH3-amine complex in THF proceeds by an analogous dissociation mechanism. In acetic acid or in the presence of mineral or Lewis acids, a bimolecular attack of the BH3-amine complex on the protonated carbonyl group has been considered to be the most viable mechanistic pathway. However, this does not account for the effect of acids on hydrolytic behavior. Consequently, caution is urged in considering possible interpretation of the acid-enhanced reactions of amine-boranes.
