Computational study of 4‐fluoro‐4‐chloro‐ and 4‐fluoro‐4‐bromo‐4‐silathiacyclohexane S‐oxides: Effect of halogen on the SO→Si intramolecular coordination in the boat and twist conformers

Chair, twist, and boat conformations of axial and equatorial 4‐fluoro‐4‐chloro‐ and 4‐fluoro‐4‐bromo‐4‐silathiacyclohexane S‐oxides have been calculated at the second‐order Møller–Plesset (MP2) and density functional theory (DFT) levels of theory. The 2,5‐twist and 1,4‐boat conformers of the axial sulfoxides are stabilized by transannular interaction between the sulfinyl oxygen and silicon to give trigonal bipyramidal geometry at silicon. The stability of conformers containing pentacoordinate silicon is governed by the balance of the transannular sulfinyl oxygen–silicon coordination, nonbonded H…H and O…Hlg_ax interactions, electronegativity of Hlg_ax and nucleofugality of Hlg_eq, and may approach the stability of the lowest‐energy chair conformers. The effect of pentacoordination on the energy and geometry of Si‐halogenated 4‐silathiane S‐oxides is analyzed as a function of the halogen nature and position. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007