An Amine–Borane System Featuring Room‐Temperature Dehydrogenation and Regeneration

Abstract

Amine–borane complexes have been extensively studied as hydrogen storage materials. Herein, we report a new amine–borane system featuring a reversible dehydrogenation and regeneration at room temperature. In addition to high purity H2, the reaction between ethylenediamine bisborane (EDAB) and ethylenediamine (ED) leads to unique boron–carbon–nitrogen 5‐membered rings in the dehydrogenation product where one boron is tricoordinated by three nitrogen atoms. Owing to the unique cyclic structure, the dehydrogenation product can be efficiently converted back to EDAB by NaBH4 and H2O at room temperature. This finding could lead to the discovery of new amine boranes with potential usage as hydrogen storage materials.

1,6;2,3-Bis-BN Cyclohexane: Synthesis, Structure, and Hydrogen Release

“…On the basis of solid state 11 B NMR spectra (Figure S18), C first transformed into intermediates consisting of both sp 2 and sp 3 B, and finally mainly sp 2 B with a broad signal typically observed for hydrogen-free BN units. 18 The solid state 1 H NMR (Figure S19) and 13 C NMR spectra (Figure S20) of final dehydrogenated products show signals related to CH 2 , which is consistent with the FTIR results. This phenomenon indicates that H 2 formation is likely driven by (N−)H•••H(−B) dihydrogen bond interactions with the subsequent formation of the B−N bond, which is consistent with previous studies.…”

“…Intensities of N–H and B–H bands decreased with heating while B–N band became stronger. On the basis of solid state 11 B NMR spectra (Figure S18), C first transformed into intermediates consisting of both sp 2 and sp 3 B, and finally mainly sp 2 B with a broad signal typically observed for hydrogen-free BN units . The solid state 1 H NMR (Figure S19) and 13 C NMR spectra (Figure S20) of final dehydrogenated products show signals related to CH 2 , which is consistent with the FTIR results.…”

“…Replacing C–C bonds with B–N bonds, forming the BN/CC isostere, has been explored to create molecules featuring different chemical and physical properties . Because of different electronegativities, there is appreciable bond polarity in B–N in comparison with C–C, which is the fundamental reason for the distinct properties in the BN-containing compounds than their carbonaceous counterparts. − For example, hexagonal boron nitride is insulating while graphite is highly conducting. , BN-containing chemicals show promising potential in many fields of applications, such as bioactive agents, − hydrogen storage, − and functional materials. − Among these, cyclic BN-containing compounds have received considerable attention due to their tunable properties. − …”

Frustrated Lewis Pair Chelation and Reactivity of Complexed Parent Iminoborane and Aminoborane

“…As with 1 , [PB­{HBNH}] ( 2 ) did not show any signs of reactivity when exposed to the dehydrogenation pre-/catalysts mentioned above. Moreover, our computations show that the B–H bond in [PB­{HBNH}] ( 2 ) is essentially nonpolar, with a computed charge at the boron-bound hydride [ Q NPA ] of only −0.04; the lack of substantial hydride character within the B–H unit in 2 would suppress its activation by metal centers as B–H bond cleavage is often postulated as an important step toward metal-mediated amine–borane dehydrogenation. , Attempted coordination of 2 by the Lewis bases DMAP, Me 3 P, and ImMe 4 (DMAP = 4-dimethylaminopyridine, ImMe 4 = (MeCNMe) 2 C:) at room temperature in THF led to no reaction. While treating 2 with the iron carbonyls, Fe­(CO) 5 and Fe 3 CO 12 , followed by photolysis with a 125 W Hg lamp in THF for 8 h, led to a complicated mixture of products according to NMR spectroscopy.…”

“…Unfortunately, most syntheses of BN involve extreme synthetic conditions, , such as temperatures above 900 °C, which make these protocols incompatible with most device fabrication methods. As a result, we have targeted the formation of possible precursors to bulk boron nitride wherein generation of reactive BN units might be possible through dehydrogenation of preformed iminoborane (HBNH) complexes (Scheme ). Free HBNH contains highly polarized B–N σ- and π-linkages; thus, rapid oligomerization of this parent species occurs under noncryogenic conditions. , In 2015, our team in collaboration with the Tokitoh group prepared the first formal complex of HBNH, IPr·HBNH·BAr 3 F ( A in Scheme ; IPr = (HCNDipp) 2 C:; Dipp = 2,6- i Pr 2 C 6 H 3 ; Ar F = 3,5-(F 3 C) 2 C 6 H 3 ), although attempts to yield a molecular BN complex via dehydrogenation failed .…”