Ammonia borane

Ammonia borane

Ball and stick model of ammonia borane
Names
IUPAC name Ammoniotrihydroborate
Other names Borazane [1] [2] [3]
Identifiers
CAS Number	13774-81-7  Y
3D model (JSmol)	Interactive image
ChemSpider	371215  Y
ECHA InfoCard	100.170.890
EC Number	642-983-4
PubChem CID	132598553
UNII	XR7O5A5MH6  Y
CompTox Dashboard (EPA)	DTXSID40422702
InChI InChI=1S/BH6N/c1-2/h1-2H3 N Key: PJYXJGDRFASJSB-UHFFFAOYSA-N N
SMILES [BH3-][NH3+]
Properties
Chemical formula	H3NBH3
Molar mass	30.87 g·mol−1
Appearance	Colorless crystals
Density	0.78 g/cm3
Melting point	104 °C (219 °F; 377 K)
Structure
Crystal structure	I4mm, tetragonal
Coordination geometry	Tetragonal at B and N
Molecular shape	Tetrahedral at B and N
Dipole moment	5.2 D
Hazards [4]
GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H228, H302, H315, H319, H332, H335
Precautionary statements	P210, P240, P241, P261, P264, P264+P265, P270, P271, P280, P301+P317, P302+P352, P304+P340, P305+P351+P338, P317, P319, P321, P330, P332+P317, P337+P317, P362+P364, P370+P378, P403+P233, P405, P501
Related compounds
Related compounds	Sodium borohydride Borazine Borane Diborane Ethane
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). N  verify  (what is  YN ?) Infobox references

Ammonia borane (also systematically named ammoniotrihydroborate^{[ citation needed ]}), also called borazane, is the chemical compound with the formula H₃NBH₃. The colourless or white solid is the simplest molecular boron-nitrogen-hydride compound. It has attracted attention as a source for hydrogen fuel, but is otherwise primarily of academic interest.

Synthesis

Reaction of diborane with ammonia mainly gives the diammoniate salt [H₂B(NH₃)₂]⁺ [BH₄]⁻ (diammoniodihydroboronium tetrahydroborate). Ammonia borane is the main product when an adduct of borane is employed in place of diborane: ^[5]

BH₃(THF) + NH₃ → BH₃NH₃ + THF

It can also be synthesized from sodium borohydride. ^{[6] [7] [8]}

Properties and structure

The molecule adopts a structure similar to that of ethane, with which it is isoelectronic. The B−N distance is 1.58(2) Å. The B−H and N−H distances are 1.15 and 0.96 Å, respectively. Its similarity to ethane is tenuous since ammonia borane is a solid and ethane is a gas: their melting points differing by 284 °C. This difference is consistent with the highly polar nature of ammonia borane. The H atoms attached to boron are hydridic (negatively charged) and those attached to nitrogen are acidic (positively charged). ^[9]

Resonance structures of ammonia-borane

The structure of the solid indicates a close association of the NH and the BH centers. The closest H−H distance is 1.990 Å, which can be compared with the H−H bonding distance of 0.74 Å. This interaction is called a dihydrogen bond. ^{[10] [11]} The original crystallographic analysis of this compound reversed the assignments of B and N. The updated structure was arrived at with improved data using the technique of neutron diffraction that allowed the hydrogen atoms to be located with greater precision.

Part of the crystal structure of ammonia borane

Comparison of bond lengths in simple boron-nitrogen hydrides

Molecule	Ammonia borane [12]	Aminoborane [13]	Iminoborane [14]
Formula	BNH6	BNH4	BNH2
Class	amine-borane	aminoborane	iminoborane
Analogous hydrocarbon	ethane	ethylene	acetylene
Analogous hydrocarbon class	alkane	alkene	alkyne
Structure
Ball-and-stick model
Hybridisation of boron and nitrogen	sp3	sp2	sp
B-N bond length	1.658 Å	1.391 Å	1.238 Å
Proportion of B-N single bond	100%	84%	75%
Structure determination method	microwave spectroscopy	microwave spectroscopy	infrared spectroscopy

Uses

Main article: Dehydrogenation of amine-boranes

Ammonia borane has been suggested as a storage medium for hydrogen, e.g. for when the gas is used to fuel motor vehicles. It can be made to release hydrogen on heating, being polymerized first to (NH₂BH₂)_n, then to (NHBH)_n, ^[15] which ultimately decomposes to boron nitride (BN) at temperatures above 1000 °C. ^[16] It is more hydrogen-dense than liquid hydrogen and also able to exist at normal temperatures and pressures. ^[17]

Ammonia borane finds some use in organic synthesis as an air-stable derivative of diborane. ^[18] It can be used as a reducing agent in transfer hydrogenation reactions, often in the presence of a transition metal catalyst. ^[19]

Analogous amine-boranes

Many analogues have been prepared from primary, secondary, and even tertiary amines:

• Borane tert-butylamine ((CH₃)₃C−NH₂→BH₃)
• Borane trimethylamine ((CH₃)₃N→BH₃)
• Borane isopropylamine ((CH₃)₂CH−NH₂→BH₃)

The first amine adduct of borane was derived from trimethylamine. Borane tert-butylamine complex is prepared by the reaction of sodium borohydride with t-butylammonium chloride. Generally adduct are more robust with more basic amines. Variations are also possible for the boron component, although primary and secondary boranes are less common. ^[8]

See also

• Tert-butylamine borane (tBuNH₂→BH₃)
• Phosphine-borane (R₃P→BH₃)
• Borane dimethylsulfide ((CH₃)₂S→BH₃)
• Borane–tetrahydrofuran (THF→BH₃)

References

1. "Method for producing borazane".
2. Umemoto, Hironobu; Miyata, Atsushi (2015). "Decomposition processes of diborane and borazane (ammonia-borane complex) on hot wire surfaces". Thin Solid Films. 8th International conference on hot-wire CVD (Cat-CVD) processes (HWCVD 8). 595: 231–234. Bibcode:2015TSF...595..231U. doi:10.1016/j.tsf.2015.04.084. hdl: 10297/10128 .
3. "Results for Borazane". sigmaaldrich.com. Retrieved 2024-09-06.
4. "Ammonia borane".
5. Shore, S. G.; Boddeker, K. W. (1964). "Large Scale Synthesis of H₂B(NH₃)₂⁺BH₄⁻ and H₃NBH₃". Inorganic Chemistry. 3 (6): 914–915. doi:10.1021/ic50016a038.
6. Hu, M.G.; Van Paasschen, J.M.; Geanangel, R.A. (January 1977). "New synthetic approaches to ammonia-borane and its deuterated derivatives". Journal of Inorganic and Nuclear Chemistry. 39 (12): 2147–2150. doi:10.1016/0022-1902(77)80383-7.
7. Ramachandran, P. Veeraraghavan; Mistry, Hitesh; Kulkarni, Ameya S.; Gagare, Pravin D. (2014). "Ammonia-mediated, large-scale synthesis of ammonia borane". Dalton Trans. 43 (44): 16580–16583. doi:10.1039/C4DT02467B. PMID   25274135.
8. Staubitz, Anne; Robertson, Alasdair P. M.; Manners, Ian (2010). "Ammonia-Borane and Related Compounds as Dihydrogen Sources". Chemical Reviews. 110 (7): 4079–4124. doi:10.1021/cr100088b. PMID   20672860.
9. Bowden, Mark E.; Gainsford, Graeme J.; Robinson, Ward T. (2007). "Room-Temperature Structure of Ammonia Borane". Australian Journal of Chemistry. 60 (3): 149. doi:10.1071/ch06442. ISSN   0004-9425.
10. Klooster, W. T.; Koetzle, T. F.; Siegbahn, P. E. M.; Richardson, T. B.; Crabtree, R. H. (1999). "Study of the N−H···H−B Dihydrogen Bond Including the Crystal Structure of BH₃NH₃ by Neutron Diffraction". Journal of the American Chemical Society . 121 (27): 6337–6343. doi:10.1021/ja9825332.
11. Boese, R.; Niederprüm, N.; Bläser, D. (1992). Maksic, Z. B.; Eckert-Masic, M. (eds.). Molecules in Natural Science and Medicine. Chichester, England: Ellis Horwood. ISBN   978-0135615980.
12. Thorne, L. R.; Suenram, R. D.; Lovas, F. J. (1983). "Microwave spectrum, torsional barrier, and structure of BH₃NH₃". J. Chem. Phys. 78 (1): 167–171. Bibcode:1983JChPh..78..167T. doi:10.1063/1.444528.
13. Sugie, Masaaki; Takeo, Harutoshi; Matsumura, Chi (1987). "Microwave spectrum and molecular structure of aminoborane, BH₂NH₂". J. Mol. Spectrosc. 123 (2): 286–292. Bibcode:1987JMoSp.123..286S. doi:10.1016/0022-2852(87)90279-7.
14. Kawashima, Yoshiyuki (1987). "Detection of HBNH by infrared diode laser spectroscopy". J. Chem. Phys. 87 (11): 6331–6333. Bibcode:1987JChPh..87.6331K. doi:10.1063/1.453462.
15. Gutowski, M.; Autrey, T. (2006). "Features: Hydrogen gets onboard". Chemistry World. 3 (3).
16. Frueh, S.; Kellett, R.; Mallery, C.; Molter; T.; Willis, W. S.; King'ondu, C.; Suib, S. L. (2011). "Pyrolytic Decomposition of Ammonia Borane to Boron Nitride". Inorganic Chemistry. 50 (3): 783–792. doi:10.1021/ic101020k. PMID   21182274.
17. Stephens, F. H.; Pons, V.; Baker, R. T. (2007). "Ammonia–Borane: The Hydrogen Source par excellence?". Dalton Transactions. 2007 (25): 2613–2626. doi:10.1039/b703053c. PMID   17576485.
18. Andrews, Glenn C.; Neelamkavil, Santhosh F. (2008). "Borane–Ammonia". In Paquette, Leo A. (ed.). Encyclopedia of Reagents for Organic Synthesis. New York: John Wiley & Sons. doi:10.1002/047084289X.rb238.pub2. ISBN   978-0471936237.
19. Zhao, Wenfeng; Li, Hu; Zhang, Heng; Yang, Song; Riisager, Anders (August 2023). "Ammonia borane-enabled hydrogen transfer processes: Insights into catalytic strategies and mechanisms". Green Energy & Environment. 8 (4): 948–971. Bibcode:2023GrEE....8..948Z. doi: 10.1016/j.gee.2022.03.011 .