Cyclopentadiene and Related Ligands

There are two filled molecular orbitals on the allyl ligand that act as good fT-donors. Thus, the allyl ligand is a four-electron donor in the donor pair electron counting formalism. 

Metal orbitals having appropriate symmetry for overlap with the 7 MOs on the allyl ligand 

Color Purple Red Amber Orange Purple Green 

One-electron MO diagram for the Cpj group orbitals in eclipsed metallocenes. 

Substituted cyclopentadienyl ligands can be used to tune the electronic properties of organometallic compounds, as well as the steric bulk of the ligand. For instance, the 1,2,3,4,5-pentamethylcyclopentadienyl ion (Cp ) is used to stabilize the Sc(lll) ion in the electron-deficient Cp 2 cX compound. Molecular orbital calculations using the ZINDO program have shown that there is significant mbdng of the 

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