Borane carbonyl explained

Borane carbonyl is the inorganic compound with the formula . 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 . The linkage is linear. The coordination geometry around the boron atom is tetrahedral. The bond distances are 114.0 pm for the bond, 152.9 pm for the bond, and 119.4 pm for the bonds. The bond angle is 113.7°. The vibrational band is at 2164.7 cm⁻¹, around 22 cm⁻¹ higher than that of free CO.^[1]

Borane carbonyl has an enthalpy of vaporization of 19.7 kJ/mol (4750 cal/mol).^[2] It has electronic state ¹A₁ and point group symmetry C_3v.^[3]

Synthesis and reactions

Borane carbonyl was discovered in 1937 by reacting diborane with excess carbon monoxide, with the equation:

.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).^[4] It can also be performed at atmospheric pressure, with ethers as a catalyst.^[5]

A more recent synthesis of borane carbonyl involves slowly bubbling carbon monoxide through a 1 M solution. The resulting gas stream can be condensed and subsequently bubbled through ethanolic potassium hydroxide to produce the boranocarbonate anion (or).^[6]

References

1. Jacobsen, H. . Berke, H. . Doering, S. . Kehr, G. . Erker, G. . Froehlich, R. . Meyer, O. . Lewis Acid Properties of Tris(pentafluorophenyl)borane. Structure and Bonding in L-B(C₆F₅)₃ Complexes. Organometallics. 1999. 18. 1724–1735. 10.1021/OM981033E.
2. Burg . Anton B. . Schlesinger . H. I. . 1937-05-01 . Hydrides of Boron. VII. Evidence of the Transitory Existence of Borine (BH 3): Borine Carbonyl and Borine Trimethylammine . Journal of the American Chemical Society . en . 59 . 5 . 780–787 . 10.1021/ja01284a002 . 0002-7863.
3. Web site: NIST Chemistry WebBook. NIST Chemistry WebBook. live. 25 October 2020. NIST Chemistry WebBook. https://web.archive.org/web/20201028205015/https://cccbdb.nist.gov/exp2x.asp?casno=13205442&charge=0 . 2020-10-28.
4. Carter . James C. . Parry . Robert W. . 1965-06-01 . The Ammonia and Alkylamine Addition Compounds of Carbon Monoxide Borane . Journal of the American Chemical Society . 87 . 11 . 2354–2358 . 10.1021/ja01089a009 . 0002-7863.
5. Mayer . Erwin . 1971-07-01 . Äther als Katalysatoren für die Reaktion von Diboran mit Lewis-Basen; vereinfachte Darstellung von Carbonylboran und Phosphinboran . Monatshefte für Chemie . de . 102 . 4 . 940–945 . 10.1007/BF00909917 . 1434-4475.
6. Alberto, R. . Ortner, K. . Wheatley, N. . Schibli, R. . Schubiger, A. P. . 2001 . Synthesis and Properties of Boranocarbonate: A Convenient in Situ CO Source for the Aqueous Preparation of [^99mTc(OH₂)₃(CO)₃]⁺ . J. Am. Chem. Soc. . 123 . 13 . 3135–3136 . 10.1021/ja003932b . 11457025.