Bis-(triphenylphosphane) Aluminum Hydride: A Simple Way to Provide, Store, and Use Non-Polymerized Alane for Synthesis.

AlH3 (PPh3 )2 was synthesized as a stable solid being the first known 1 : 2 alane arylphosphane adduct. Although only weakly intra-molecularly coordinated, it displays as a molecular crystal significant inertness against atmospheric humidity and oxygen due to strong steric screening of the alane unit. The compound readily dissociates PPh3 in solution allowing for its use as a Lewis acidic reducing agent. These features lead to an easy to store, easy to use reducing agent that may enable the quantitative investigation of aluminum hydride chemistry including reduction, complexation and hydroalumination reactions. The structure contains two non-equivalent penta-coordinated aluminum centers that despite long Al-P distances of ca. 2.7 Šdisplay unusually high quadrupolar coupling constants CQ of 25.1 and 26.5 in 27 Al solid state NMR measurements. The product was also tested as a reducing agent on a small set of selected compounds with various functional groups.

The direct and reversible hydrogenation of activated aluminium supported by piperidine.

The reversible hydrogenation of aminoalanes employing activated aluminium and piperidine has been explored. A selection of transition metal (TM) compounds have been investigated as additives for producing TM-activated aluminium (TM = Ti, Zr, Hf and Y). The effect of these additives on the activation of aluminium with respect to hydrogenation of an aluminium/piperidinoalane system has been studied. It has been shown that Ti, Zr and Hf can efficiently promote the activation of aluminium for its hydrogenation. The experiments performed showed that the TM activity for the piperidinoalane formation decreases in the order Zr > Hf > Ti > Y. Using multinuclear NMR spectroscopy, the reversibility of this piperidinoalane-based hydrogenation system has been evidenced, demonstrating a potential pathway for hydrogen storage in aminoalanes. The syntheses of piperidinoalanes as well as their structural and spectroscopic characterisation are described. Single-crystal X-ray diffraction analyses of [pip2AlH]2 and [pip3Al]2 (pip = 1-piperidinyl, C5H10N) revealed dimers containing a central [AlN]2 unit.

Direct Hydrogenation of Aluminum via Stabilization with Triethylenediamine: A Mechanochemical Approach to Synthesize the Triethylenediamine ⋠AlH3 Adduct.

Two approaches for the synthesis of the triethylenediamine (TEDA) ⋅ AlH3 adduct have been discovered. Both, the mechanochemical procedure and the wet chemical method lead to crystalline products. Starting from metallic Al powder and TEDA, ball milling under a pressure of 100 bar H2 facilitates a direct hydrogenation of aluminum with conversions up to 90 %. Structure determination from X-ray powder diffraction data revealed an 1-D-coordination polymer of the type [TEDA-AlH3 ]n . Furthermore, solid-state NMR techniques have been applied to analyze composition and structure of the products. Due to the polymeric arrangement, an enhanced stability of the material occurred which was investigated by thermal analysis showing a decomposition located above 200 °C. Overall, the stabilization of AlH3 by TEDA holds promise for hydrogen storage applications.