A density functional study of ethylene rearrangements assisted by tungstencalix[4]arenes

Density functional calculations have been performed on all complexes involv ed in the rearrangements undergone by ethylene on the calix[4]arene tungste n fragment. [{p-Bu-t-calix[4](O)(4)}W(eta (2)-C2H4)], which is the starting reactant of the rearrangement process, has been carefully investigated. In order to reduce the computational effort a simplified model of tungsten ca lix[4]arene has been considered. Preliminary calculations have shown that f our vinylate groups reproduce adequately the geometrical, electronic, and b onding parameters of the calix[4]arene ligand so that we have employed the {(C2H3O)(4)}W fragment to investigate the ethylene rearrangements. Calculat ed geometrical and thermodynamical data obtained for ethylene rearrangement s agree with the experimental X-ray data and the observed reaction trend.