Electronic effects of icosahedral carboranes: kinetic evidence for interaction between boron atom and nucleophile in the solvolysis of (o-carboranyl)benzyl tosylates

Solvolysis of (o-, m- and p-carboranyl)benzyl toluene-p-sulfonates substituted at the second carbon atom with a phenyl group bearing a range of substituents at the para position has been performed. The rates of hydrolysis of m- and p-carboranyl derivatives measured linearly with increasing electron-releasing character of the substituent group (ρ=−0.23, ρ=−0.35), which indicates that these carboranes transmit electronic effects, and the substituents affect the stability of the neighboring carbocation. In contrast, the rate of hydrolysis of o-carboranyl derivatives showed a linear decrease with increasing electron-releasing character of the substituent (ρ=+1.12), which indicates that the interaction between the B(3) atom of the o-carborane cage and the nucleophile controls this particular reaction.