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An alkene ligand commonly binds through both double-bond carbons, ${\eta }^2$. The balance of donation and backbonding is described by the Dewar-Chatt-Duncanson model.

Methyl abstraction transfers a metal-bound methyl group to an electrophile. A trityl cation can convert a neutral metallocene dimethyl into a cationic monomethyl, forming $\mathrm{P}{\mathrm{h}}_3\mathrm{CMe}$ and opening a site for an alkene ligand.

The filled alkene $\pi$ molecular orbital donates into a vacant metal acceptor orbital directed toward the center of the C=C bond. In the reverse direction, a filled metal $d$ orbital can overlap with the alkene ${\pi }^{\ast }$ antibonding molecular orbital. These are the donation and pi backbonding components of the Dewar-Chatt-Duncanson model, illustrated in the lower part of the bonding schematic. The alkene is an ${\eta }^2$ alkene ligand, attached through both carbons. Increasing backbonding weakens and lengthens C=C and can push the bonding toward a metallacyclopropane description.

Zr(IV) is $d^0$, so alkene-to-metal donation predominates. It has suitable empty orbitals but no occupied metal $d$ set to provide substantial conventional backbonding. An electron-deficient cationic zirconocene can consequently bind and activate an alkene largely through its Lewis acidity; it should not be drawn as a strongly backbonded late-metal alkene merely because its formal coordination mode is ${\eta }^2$.