Lewis Acid-Assisted Generation of Iodenium(I) Ions: A Computational Approach

The problem of Lewis acid assisted generation of iodenium(I) cations from I2 and ICl is computationally addressed at the M06–2X/def2-TZVP level of theory in the gas phase and in solutions using the SMD model. Molecular and ionic complexes of I2 and ICl with SbCl5, SbF5 and bora/alatriptycenes were considered. Boratriptycene and its analogs form quite stable molecular complexes with such Lewis bases (LB) as Et2O, THF and MeCN, which precludes formation of molecular complexes with I2 and ICl. With the exception of B(C6F4)3CF, the process of halogenation of B–C/Al–C bonds by I2 and ICl is predicted to be thermodynamically favorable, which limits the practical use of bora/alatriptycenes for the generation of iodonium cations. In the case of SbX5, in the presence of donor solvents I3+ and I2Cl+ cations readily form [I(LB)2]+···[SbX5X′]− contact ion pairs (X′ = I,Cl). In the case of I2 molecular complexes are predicted to be preferable, while in the case of ICl, an equilibrium between ionic and molecular forms is predicted. In CCl4, generation of the contact ion pairs I2Cl+···[SbF5Cl]− and I3+···[SbF5I]− is exergonic. The system SbF5–ICl in nonpolar solvents with weak donor properties is expected to be promising for experimental studies.