On the comparative reactivity of carboranes (B₁₀H₁₀C₂H₂), carbaphosphaboranes (B₁₀H₁₀PCH), and carbaarsaboranes (b₁₀h₁₀asch)

Conclusions

• 1. o-, m-, and p-Carbaarsaboranes undergo electrophilic halogenation, exchangehalogenation with polychloromethanes, and photochemical chlorination at the boron atoms of the carbaarsaborane ring.

• 2. The ease of electrophilic halogenation of the carbaarsaborane isomers decreases in the series: ortho- > meta- > para isomers, and the stability of the carbaarsaborane ring toward piperidine increases in the series: ortho- < meta- < para isomers.

• 3. The halogenation rate of the carbaarsaborane isomers is greater than it is for the corresponding carborane and carbaphosphaborane isomers, and the carbaarsaborane ring is more stable toward piperidine than the carborane and carbaphosphaborane rings.

• 4. A mixture of 8(10)-, 9-, and 12-halogeno-o-carbaarsaboranes is formed during the electrophilic and exchange monohalogenation of o-carbaarsaborane, and a mixture of the six possible B-chloro-o-carbaarsaboranes is formed during the photochemical monochlorination.

• 5. Isomerization of o-carbaarsaborane into m-carbaarsaborane takes place in the gas phase at 550°C in a 96% yield, and at 650°C, the m- and p-carbaarsaboranes are mutually converted into each other yielding an equilibrium mixture containing 50% p-carbaarsaborane.