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 (rho = -0.23, rho = -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 (rho = +1.12), which indicates that the interaction between the B(3) atom of the o-carborane cage and the nucleophile controls this particular reaction. (C) 2001 Elsevier Science Ltd. All rights reserved.