Isomerism of Cp-containing transition metal allyl complexes

The isomerism of Cp-containing transition metal η³-allyl complexes has been investigated with the aid of density functional theory calculations. The effect of ligands and numbers of metal d electrons on the isomerism has been examined and discussed in detail. Our studies show that d⁶-CpML(η³-allyl) (L = CO, PR₃, N≡CR, alkyl, hydride, halides) complexes preferentially adopt exo structural isomers in which the central allylic hydrogen (or substituent) of the η³-allyl ligand points toward the Cp ring. However, when L = ≠²-olefin, an endo form is preferred. For d⁴-CpML ₂(η³-allyl) (L ≠ CO) complexes, endo isomers are preferred. When L = CO, endo and exo isomers have comparable stability. Orbital interaction models have been proposed to explain the different isomerism behaviors of the complexes.