The Lewis acidity of bismuth(III) halides: a DFT analysis

The Lewis acidity of BiX3 (X=Cl, Br, I) is explored using density-functional theory (DFT) studies of simple complexes with various alcohol and carbonyl substrates. The calculated relative energies of the complexes follow the trend of hardness for BiX3 (Cl>Br>I). The observed halogen exchange reaction of BiCl3 with alcohols and alkyl halides is discussed in terms of the computational results as well as theories of hardness and carbocation stability. The DFT results predict similar activation of substrates by molecular BiI3 relative to BiBr3, which is inconsistent with experimental results, which show no reactivity for the iodide in nonpolar solvents. However, the molecular form is unlikely in these solvents as BiI3 is an ionic salt in contrast to the chloride and bromide, which are covalent solids.