Complexation of Ammonia Boranes with Al³⁺

Abstract

Ammonia borane, NH3BH3 (AB), is very attractive for hydrogen storage; however, it dehydrogenates exothermally, producing a mixture of polymeric products with limited potential for direct rehydrogenation. Recently, it was shown that AB complexed with Al3+ in Al­(BH4)3·AB endothermically dehydrogenates to a single product identified as Al­(BH4)3·NHBH, with the potential for direct rehydrogenation of AB. Here we explore the reactivity of AB-derived RNH2BH3 (R = −CH3, −CH2−) with AlX3 salts (X = BH4 –, Cl–), aiming to extend the series to different anions and to enlarge the stability window for Al­(BH4)3·NRBH. Three novel complexes were identified: Al­(BH4)3·CH3NH2BH3 having a molecular structure similar to that of Al­(BH4)3·AB but different dehydrogenation properties, as well as [Al­(CH3NH2BH3)2Cl2]­[AlCl4] and [Al­(NH2CH2CH2NH2)­(BH4)2]­[Al­(BH4)4], rare examples of Al3+ making part of the cations and anions simultaneously. The latter compounds are of interest in the design of novel electrolytes for Al-based batteries. The coordination of two ABs to a single Al atom opens a route to materials with higher hydrogen content.

Monocyclopentadienyltitanium(III) Complexes with Hydridoborato Ligands

“…Both BH 4 groups are bidentate as in many other aluminum complexes with tetrahydridoborato ligands. However, the Al···B distances of 2.303(3) Å in 14 are slightly longer than those observed in aluminum complexes with κ 2 -coordinated BH 4 units (2.10(1)–2.27(8) Å). , …”

Aluminum methylamidoborane complexes: mechanochemical synthesis, structure, stability, and reactive hydride composites

“…MeAB was obtained through a procedure adapted from the literature. 55 In brief, the synthesis was performed as follows. Powdered NaBH 4 (3.79 g, 0.1 mol), CH 3 NH 2 ·HCl (13.50 g, 0.1 mol), and THF (300 mL) were added to a 500 mL, three-neck, round-bottom flask.…”

Encapsulation of Ammonia Borane in Pd/Halloysite Nanotubes for Efficient Thermal Dehydrogenation

“…As one of the most ideal chemical hydrogen storage materials, ammonia borane (NH 3 BH 3 , AB) has particularly aroused widespread attention. It is stable at normal pressure and temperature and produces 19.6 wt % hydrogen theoretically, which meets the U.S. Department of Energy’s goal for hydrogen storage. − Generally, there are two dehydrogenation processes for catalysis of AB: hydrolysis and pyrolysis. Compared to hydrolysis in a solid–liquid system, the anhydrous pyrolysis in a solid–gas system is more desirable for practical on-board applications owing to its simple equipment design, safety, and convenient transportation and recently realized regenerability of a thermolysis reaction product .…”