Mechanism of the allylic rearrangement of allyloxo metal oxo complexes: Anab initio theoretical investigation

The mechanism of the isomerization of allyl alcohols by the 1,3-transpositi on of a hydroxy group, which is catalyzed by transition metal complexes in a high oxidation state, has been investigated by ab initio quantum chemical calculations for a trioxorhenium catalyst. The calculations point to a cyc lic transition state that consists of a perrhenate anionic moiety and an al lylic cationic group. This is similar to the transition state found for the [3,3] sigmatropic rearrangement in allyl formate. The energy barrier is lo wer in the organometallic case. The calculations also suggest that the kine tic discrimination that is observed experimentally for the catalyzed cis-tr ans isomerization of hex-1-en-3-ol is due to microsolvation effects of the corresponding transition states by the alcohols that are present in the rea ction medium. All these features are explained in terms of orbital interact ions present in the transition state.