Borane carbonyl

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.

Structure and properties
The structure of the molecule of borane carbonyl is H3B−\sC\tO+. The B\sC\tO linkage is linear. The coordination geometry around the boron atom is tetrahedral. The bond distances are 114.0 pm for the C\tO bond, 152.9 pm for the C\sB bond, and 119.4 pm for the B\sH bonds. The H\sB\sH bond angle is 113.7°. The C\tO vibrational band is at 2164.7 cm−1, around 22 cm−1 higher than that of free CO.

Borane carbonyl has an enthalpy of vaporization of 19.7 kJ/mol (4750 cal/mol). It has electronic state 1A1 and point group symmetry C3v.

Synthesis and reactions
Borane carbonyl was discovered in 1937 by reacting diborane with excess carbon monoxide, with the equation:
 * B2H6 + 2 CO ⇌ 2 BH3CO.

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). It can also be performed at atmospheric pressure, with ethers as a catalyst.

A more recent synthesis of borane carbonyl involves slowly bubbling carbon monoxide through a 1 M H3B\sTHF solution. The resulting gas stream can be condensed and subsequently bubbled through ethanolic potassium hydroxide to produce the boranocarbonate anion ([H3BCO2](2-) or H3B−\sCO2−).