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.