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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.

The Dewar-Chatt-Duncanson model describes an alkene–metal bond through donation from the filled alkene $\pi$ orbital to the metal and pi backbonding from the metal into alkene ${\pi }^{\ast }$. Backbonding weakens and lengthens the alkene double bond. A $d^0$ early-metal ion has little conventional $d$-electron backbonding.

The Dewar-Chatt-Duncanson model has two complementary interactions. The filled alkene $\pi$ orbital donates to an empty metal orbital, and an occupied metal $d_{\pi }$ orbital back-donates into the empty alkene ${\pi }^{\ast }$ orbital. The metal acceptor has the symmetry of the sum of the two ligand lobes facing it; the back-donor has opposite phases at the two carbon positions and matches the antisymmetric ${\pi }^{\ast }$ combination.Both channels strengthen metal–alkene attachment. Donation removes some electron density from the internal bonding orbital, while back-donation populates its antibonding partner, so coordination generally reduces C–C bond order. The schematic shows orbital phase signs, not positive and negative electric charges.

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 ${\eta }^2$.