Quantification of the Trans Influence in Hypervalent Iodine Complexes

Abstract

The trans influence of various X ligands in hypervalent iodine(III) complexes of the type CF3[I(X)Cl] has been quantified using the trans I–Cl bond length (dX), the electron density ρ(r) at the (3, −1) bond critical point of the trans I–Cl bond, and topological features of the molecular electrostatic potential (MESP). The MESP minimum at the Cl lone pair region (Vmin) is a sensitive measure of the trans influence. The trans influence of X ligands in hypervalent iodine(V) complexes is smaller than that in iodine(III) complexes, while the relative ordering of this influence is the same in both complexes. In CF3[I(X)Y] complexes, the mutual trans influence due to the trans disposition of the X and Y ligands is quantified using the energy EXY of the isodesmic reaction CF3[I(X)Cl] + CF3[I(Y)Cl] → CF3[I(Cl)Cl] + CF3[I(X)Y]. EXY is predicted with good accuracy using the trans-influence parameters of X and Y, measured in terms of dX, ρ(r), or Vmin. The bond dissociation energy (Ed) of X or Y in CF3[I(X)Y] is significantly influenced by the trans influence as well as the mutual trans influence. This is confirmed by deriving an empirical equation to predict Ed using one of the trans-influence parameters (dX, ρ(r), or Vmin) and the mutual trans-influence parameter EXY for a large number of complexes. The quantified values of both the trans influence and the mutual trans-influence parameters may find use in assessing the stability of hypervalent iodine compounds as well as in the design of new stable hypervalent complexes. Knowledge about the I–X bond dissociation energies will be useful for explaining the reactivity of hypervalent iodine complexes and the mechanism of their reactions.