Bonding in Olefin Complexes

Other olefin complexes are stabilized considerably by donation of electron density from the metal d-orbital into the unoccupied ir -orbital of the olefin. Olefins are predominantly TT-acceptors in complexes that possess electron-rich metal centers, such as those in low formal oxidation states. Like the interaction of the ii -orbital of CO with a filled metal d-orbital, the interaction of tiie ir -orbital of an olefin with a filled orbital at tire metal leads to a flow of electron density into the ir -orbital of the ligand and reduces the bond order of the ir-bond in the ligand. 

the carbon-carbon bond order of the olefin in such a complex deaeases upon coordination, and tire C-C bond length is longer than that of the free olefin. In addition, the hybridization at the olefinic carbons increases from sp toward sp, and the substituents on the olefim are bent away from tiie metal. Such olefin ligands imdergo electrophilic attack, as is discussed in Chapter 12. 

Orbital interactions in the Chatt-Dewar-Duncanson bonding model of olefin binding. 

Olefin complex and metallacyclopropane resonance structures and examples of complexes with predominantly olefin character and predominantly metallacyclopropane character. 

Alkyne complex and metallacy-clopropene resonance forms. 

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