Hydrogen storage for transportation applications requires high volumetric and gravimetric storage capacity. B-N compounds are well suited as storage materials due to their light weight and propensity for bearing multiple protic (N-H) and hydridic (B-H) hydrogens. This critical review briefly covers the various methods of hydrogen storage, and then concentrates on chemical hydrogen storage using B-N compounds. The simplest B-N compound, ammonia borane (H3NBH3), which has a potential 19.6 wt% hydrogen storage capacity, will be emphasised (127 references).

Ammonia-borane (NH(3)BH(3), AB) has garnered interest as a hydrogen storage material due to its high weight percent hydrogen content and ease of H(2) release relative to metal hydrides. As a consequence of dehydrogenation, B-N-containing oligomeric/polymeric materials are formed. The ability to control this process and dictate the identity of the generated polymer opens up the possibility of the targeted synthesis of new materials. While precious metals have been used in this regard, the ability to construct such materials using earth-abundant metals such as Fe presents a more economical approach. Four Fe complexes containing amido and phosphine supporting ligands were synthesized, and their reactivity with AB was examined. Three-coordinate Fe(PCy(3))[N(SiMe(3))(2)](2) (1) and four-coordinate Fe(DEPE)[N(SiMe(3))(2)](2) (2) yield a mixture of (NH(2)BH(2))(n) and (NHBH)(n) products with up to 1.7 equiv of H(2) released per AB but cannot be recycled (DEPE = 1,2-bis(diethylphosphino)ethane). In contrast, Fe supported by a bidentate P-N ligand (4) can be used in a second cycle to afford a similar product mixture. Intriguingly, the symmetric analogue of 4 (Fe(N-N)(P-P), 3), only generates (NH(2)BH(2))(n) and does so in minutes at room temperature. This marked difference in reactivity may be the result of the chemistry of Fe(II) vs Fe(0).

New 1,10-phenanthroline ligands have been synthesized with C6F5- or 2,4,6-(CF3)3C6H2- groups in the 2- and 9-positions; a cationic copper(I) complex of the latter catalyses nitrene transfer to the C-H bonds of electron-rich arenes.

NotesVol. 70 enediamine |di hydrochloride was found to be 0.86 c./m./ mg. This indicates that 2.6% of the succinic acid radioactivity was in the methylene carbon atoms.Oxidation of Malic Acid.-To a solution of 109.7 mg. of C14-labeled malic acid (275 c./m./mg. or 30,100 c./m. total.) in 10 ml. of 1.0 N sulfuric acid in a 100-ml. flask equipped with nitrogen inlet bubbler, reflux condenser and dropping funnel was added 20 ml. of 0.15 M chromic acid solution during two hours on the steam-bath.The carbon dioxide evolved was collected in carbonatefree sodium hydroxide solution and precipitated with barium chloride to give 326 mg. (101%) of barium carbonate.The specific activity was found to be 81.5 c./m./mg. or 26,600 c./m. total. Acetic acid was obtained from the residual solution upon steam distillation. It was converted to barium acetate (80% yield based on titer of steam distillate) which was recrystallized from water. From the specific activity (2.0 c./m./mg.) and the theoretical yield (112 mg.), the activity in the a and /3 carbon atoms of the malic acid, 224 c./m., can be determined accurately without interference from carboxyl activity. Incomplete recovery of the carbon dioxide and overoxidation of the malic acid is assumed to have caused the loss of carboxyl activity.

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