given: Ferrocene, Acetylferrocene, 1, 1' Diacetylferrocene
What part of the ferrocene compound(s) is(are) responsible for creating a dipole moment
What type of molecular orbitals does the cyclopentadienyl ligand use to bond with the iron ion? How many electron pairs does each cyclopentadienyl ligand donate to the iron ion?
Matt, thank you for your question. I understand that I am eight years too late, and that this may no longer be useful. However, for whoever next stumbles on this website, the consensus is that 1-1' diacetylferrocene is more polar than acetylferrocene, which is more polar than ferrocene.
To determine the part of the ferrocene compound(s) responsible for creating a dipole moment, we need to consider the molecular structure of each compound.
Ferrocene consists of two cyclopentadienyl (Cp) rings bound to an iron (Fe) atom. The Cp rings are aromatic and do not possess a dipole moment since the charge distribution is symmetric around the ring.
Acetylferrocene is derived by substituting one of the hydrogen atoms on the Cp ring with an acetyl group (-COCH3). In this case, the dipole moment is mainly attributed to the polar carbonyl (C=O) group, which has a partial positive charge on carbon and a partial negative charge on oxygen.
In 1,1'-Diacetylferrocene, both hydrogen atoms on the Cp ring are substituted with acetyl groups. Similar to Acetylferrocene, the dipole moment arises primarily from the polar carbonyl groups of the acetyl groups.
Therefore, in both Acetylferrocene and 1,1'-Diacetylferrocene, the acetyl groups (C=O) are responsible for creating the dipole moment.
Regarding the type of molecular orbitals (MOs) that the cyclopentadienyl ligand uses to bond with the iron ion, the Cp ligand donates its π-electrons to form π-bonding interactions with the iron atom. Since cyclopentadienyl is aromatic, it contains a ring of six π-electrons, which occupy three π-orbitals.
The iron ion in ferrocene has available d-orbitals for bonding. The interaction occurs between the filled π-orbitals of the Cp rings and the empty d-orbitals of the iron ion. This overlap forms π-d bonding orbitals.
Each cyclopentadienyl ligand donates one pair of π-electrons to the iron ion, resulting in a total of two electron pairs donated by both ligands.