Borane carbonyl is the inorganic compound with the formula H3BCO. This colorless gas is the adduct of borane and carbon monoxide. It is usually prepared by combining borane-ether complexes and CO. The compound is mainly of theoretical and pedagogical interest.[2]
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| Names | |
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| IUPAC name Borane carbonyl | |
Other names
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| Identifiers | |
3D model (JSmol) | |
| ChemSpider | |
PubChem CID | |
CompTox Dashboard (EPA) | |
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| Properties | |
| H3BCO | |
| Molar mass | 41.84 g·mol−1 |
| Appearance | colorless gas |
| Density | 1.71 g/L[1] |
| Melting point | −137[1] °C (−215 °F; 136 K) |
| Boiling point | −64[1] °C (−83 °F; 209 K) |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). | |
Structure and properties
The structure of the molecule of borane carbonyl is H3B−−C≡O+. The B−C≡O linkage is linear. The coordination geometry around the boron atom is tetrahedral. The bond distances are 114.0 pm for the C≡O bond, 152.9 pm for the C−B bond, and 119.4 pm for the B−H bonds. The H−B−H bond angle is 113.7°. The C≡O vibrational band is at 2164.7 cm−1, around 22 cm−1 higher than that of free CO.[3]
Borane carbonyl has an enthalpy of vaporization of 19.7 kJ/mol (4750 cal/mol).[4] It has electronic state 1A1 and point group symmetry C3v.[5]
Synthesis and reactions
Borane carbonyl was discovered in 1937 by reacting diborane with excess carbon monoxide, with the equation:
- B2H6 + 2 CO ⇌ 2 BH3CO.[4]
The reaction quickly reaches equilibrium at 100°C, but at room temperature, the reverse reaction is slow enough to isolate borane carbonyl. This reaction is performed at high pressures, typically with a maximum pressure observed of 1000 to 1600 psi (68.95 to 110.32 bar).[6] It can also be performed at atmospheric pressure, with ethers as a catalyst.[7][8]
A more recent synthesis of borane carbonyl involves slowly bubbling carbon monoxide through a 1 M H3B−THF solution. The resulting gas stream can be condensed and subsequently bubbled through ethanolic potassium hydroxide to produce the boranocarbonate anion ([H3BCO2]2− or H3B−−CO−2).[8]