Tetrahydroxydiboron

Tetrahydroxydiboron

Names
IUPAC name Hypoboric acid [1]
Other names (Dihydroxyboranyl)boronic acid Hypoboric acid Hypodiboric acid Sub-boric acid (Unterborsäure in German) 1,1,2,2-Tetrahydroxydiborane
Identifiers
CAS Number	13675-18-8  Y
3D model (JSmol)	Interactive image
ChEBI	CHEBI:38289
ChemSpider	9161351
ECHA InfoCard	100.222.662
PubChem CID	10986154
UNII	D0Q7FO865W  Y
CompTox Dashboard (EPA)	DTXSID40450702
InChI InChI=1S/B2H4O4/c3-1(4)2(5)6/h3-6H Key: SKOWZLGOFVSKLB-UHFFFAOYSA-N
SMILES B(B(O)O)(O)O
Properties
Chemical formula	B2H4O4
Molar mass	89.65 g·mol−1
Appearance	White powder
Density	1.657
Solubility in water	very soluble
Solubility	ethanol, DMF, DMSO, DMA
Structure
Crystal structure	monoclinic P21/c
Thermochemistry
Std molar entropy (S⦵298)	125.46 J K−1 mol−1
Std enthalpy of formation (ΔfH⦵298)	−1410.43 kJ mol−1
Hazards
GHS labelling:
Hazard statements	H302, H315, H319, H332, H335
Precautionary statements	P261, P264, P270, P271, P280, P301+P312, P302+P352, P304+P312, P304+P340, P305+P351+P338, P312, P321, P330, P332+P313, P337+P313, P362, P403+P233, P405, P501
Related compounds
Related compounds	Diborane Diboron tetrafluoride Bis(pinacolato)diboron
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Tetrahydroxydiboron is a reagent which has several uses in organic synthesis, ^[2] notably as a precursor for boronic acids used in Suzuki-Miyaura couplings ^[3]

Synthesis

The reaction of boron trichloride with alcohols was reported in 1931, and was used to prepare dimethoxyboron chloride, B(OCH₃)₂Cl. ^[4] Egon Wiberg and Wilhelm Ruschmann used it to prepare tetrahydroxydiboron by first introducing the boron–boron bond by reduction with sodium and then hydrolysing the resulting tetramethoxydiboron, B₂(OCH₃)₄, to produce what they termed sub-boric acid. ^[5] The methanol used in this process can be recycled:

BCl₃ ${\displaystyle {\ce {->[{\text{+ }}{\ce {CH3OH}}][-{\text{ }}{\ce {HCl}}]}}}$  B(OCH₃)₂Cl  ${\displaystyle {\ce {->[{\text{+ }}{\ce {Na}}][-{\text{ }}{\ce {NaCl}}]}}}$  B₂(OCH₃)₄ ${\displaystyle {\ce {->[{\text{+ }}{\ce {H2O}}][-{\text{ }}{\ce {CH3OH}}]}}}$  B₂(OH)₄

Overall: 2  BCl₃  + 2  Na  + 4  H₂O  → B₂(OH)₄ + 2  NaCl  + 4  HCl

Reactions

Tetrahydrodiboron can be used in the Miyaura borylation of aryl halides and psuedo-halides to form aryl boronic acids, ^[6] which are key components in Suzuki-Miyaura couplings. ^[7] Tetrahydroxydiboron has also been shown to be a reducing agent for nitro groups, providing an alternative to reactions involving hydrogen gas. ^[8]

Safety

Although tetrahydroxydiboron has been shown not to be shock or friction sensitive in the solid state, differential scanning calorimetry shows the compound decomposes with significant energy release starting at 90 °C, ^[9] which may be related to the dehydration to a polymeric boron(II) oxide. ^[10] Similar thermal instability is observed in solution with organic solvents like DMF and DMSO. ^[11] An additional safety consideration when using tetrahydroxydiboron is that upon exposure to water, tetrahydroxydiboron decomposes to form for two equivalents of boric acid and one equivalent of hydrogen gas. ^[12]

References

1. "Hypodiboric acid". IUPAC.
2. Zhao, Qiuxia; Liu, Xiang; Astruc, Didier (2023). "Tetrahydroxydiboron (Bis-boric Acid): a Versatile Reagent for Borylation, Hydrogenation, Catalysis, Radical Reactions and H2 Generation". European Journal of Inorganic Chemistry. 26 (11): e202300024. doi: 10.1002/ejic.202300024 . ISSN   1099-0682.
3. Little, Sarah; Trice, Jane (2001). "Tetrahydroxydiboron". Encyclopedia of Reagents for Organic Synthesis . John Wiley & Sons. doi:10.1002/047084289x.rn01181. ISBN   9780470842898.
4. Wiberg, Egon; Sütterlin, Walther (1931). "Zur Kenntnis einiger Verbindungen vom Typus BCl_3−n(OR)_n. (Über alkoxyl-substituierte Borchloride)" [Notes on some compounds of type BCl_3−n(OR)_n. (Via alkoxy-substituted boron chlorides)]. Z. anorg. allg. Chem. (in German). 202 (1): 1–21. doi:10.1002/zaac.19312020102.
5. Wiberg, Egon; Ruschmann, Wilhelm (1937). "Über eine neue Borsäure ('Unterborsäure'︁) der Formel H₄B₂O₄ und ihre Ester" [On a new boric acid ('Sub-boric acid') of the formula H₄B₂O₄ and its esters]. Ber. Dtsch. Chem. Ges. A/B (in German). 70 (6): 1393–1402. doi:10.1002/cber.19370700636.
6. Chow, Wing Kin; Yuen, On Ying; Choy, Pui Ying; So, Chau Ming; Lau, Chak Po; Wong, Wing Tak; Kwong, Fuk Yee (2013-07-15). "A decade advancement of transition metal-catalyzed borylation of aryl halides and sulfonates" . RSC Advances. 3 (31): 12518–12539. doi:10.1039/C3RA22905J. ISSN   2046-2069.
7. Chow, Wing Kin; Yuen, On Ying; Choy, Pui Ying; So, Chau Ming; Lau, Chak Po; Wong, Wing Tak; Kwong, Fuk Yee (2013-07-15). "A decade advancement of transition metal-catalyzed borylation of aryl halides and sulfonates" . RSC Advances. 3 (31): 12518–12539. doi:10.1039/C3RA22905J. ISSN   2046-2069.
8. Jang, Mingyeong; Lim, Taeho; Park, Byoung Yong; Han, Min Su (2022-01-21). "Metal-Free, Rapid, and Highly Chemoselective Reduction of Aromatic Nitro Compounds at Room Temperature" . The Journal of Organic Chemistry. 87 (2): 910–919. doi:10.1021/acs.joc.1c01431. ISSN   0022-3263.
9. Zhang, Shasha; Leung, Simon Shun Wang; Vanyo, Dale (2024-07-19). "Thermal Stability of Tetrahydroxydiboron" . Organic Process Research & Development. 28 (7): 2854–2861. doi:10.1021/acs.oprd.4c00159. ISSN   1083-6160.
10. Wartik, Thomas; Apple, Eugene F. (1955-12-01). "A NEW MODIFICATION OF BORON MONOXIDE" . Journal of the American Chemical Society. 77 (23): 6400–6401. doi:10.1021/ja01628a116. ISSN   0002-7863.
11. Revu, Omkar; Vasilev, Maksim; Gajula, Praveen; Kalikinidi, Nageswara Rao; Gadi, Madhusudhan Reddy; Zhao, Huiping; Gamage, Shanika M. P.; Hibbert, Graham; Ravikumar, Ongolu; Gummidi, Lalitha; Nasipireddy, Venkatarathnam; Vinodini, Arun; Bietsch, Jonathan; Wang, Zhirui; Brown, Jack D. (2024-10-18). "Development of a Safer Continuous Flow Process for B2(OH)4-Mediated Chemoselective Reduction of Nitroarenes to Anilines" . Organic Process Research & Development. 28 (10): 3847–3857. doi:10.1021/acs.oprd.4c00267. ISSN   1083-6160.
12. Merritt, Jeremy M.; Borkar, Indrakant; Buser, Jonas Y.; Brewer, Alison Campbell; Campos, Odilon; Fleming, Jeffrey; Hansen, Caoimhe; Humenik, Ashley; Jeffery, Stephen; Kokitkar, Prashant B.; Kolis, Stanley P.; Forst, Mindy B.; Lambertus, Gordon R.; Martinelli, Joseph R.; McCartan, Ciaran (2022-03-18). "Hydrogen Evolution from Telescoped Miyaura Borylation and Suzuki Couplings Utilizing Diboron Reagents: Process Safety and Hazard Considerations" . Organic Process Research & Development. 26 (3): 773–784. doi:10.1021/acs.oprd.1c00198. ISSN   1083-6160.