Borabenzene is a hypothetical organoboron compound with the formula C<sub>5</sub>H<sub>5</sub>B. Unlike the related but highly stable benzene molecule, borabenzene would be electron-deficient. Related derivatives are the boratabenzene anions, including the parent [C<sub>5</sub>H<sub>5</sub>BH]<sup>−</sup>.
Adducts
Adducts of borabenzene with Lewis bases are isolatable. Since borabenzene is unavailable, these adducts require indirect methods. 4-Silyl-1-methoxyboracyclohexadiene is used as a precursor to the borabenzene:
: + → + MeOSiMe<sub>3</sub>
The pyridine adduct is structurally related to biphenyl. It is a yellow whereas biphenyl is colorless, indicating distinct electronic structures. The pyridine ligand is tightly bound: no exchange is observed with free pyridine, even at elevated temperatures.
:left|thumb|150px|Adducts of borabenzene with pyridine and triphenylphosphine.
The borabenzene-pyridine adduct behaves like a diene, not an analog of biphenyl, and will undergo Diels-Alder reactions.
:500px|Borabarrelene synthesis via a Diels-Alder reaction of borabenzene-pyridine adduct
See also
- 6-membered aromatic rings with one carbon replaced by another group: silabenzene, germabenzene, stannabenzene, pyridine, phosphorine, arsabenzene, stibabenzene, bismabenzene, pyrylium, thiopyrylium, selenopyrylium, telluropyrylium
- Borazine
- Hexachloroborazine