Can the cyclo-P5 Ligand Introduce Basicity at the Transition Metal Center in Metallocenes?

What is it about?

Density functional theory (DFT) calculations and natural population analysis (NPA) performed on metallocenes of Fe, Ru and Os triad reveal that the cyclo-P5 ligand introduces basicity at the metal center. All-electron calculations at the B3LYP/6-311+G* level yield NPA charges of 0.28, −0.28 and −0.91 at the iron center in [FeCp2], [FeCp(η5-P5)] and [Fe(η5- P5)2], respectively.

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Why is it important?

There is a small transfer of electron density from each phosphorus atom to the metal center, leading to a significant build-up of negative charge on the metal in [M(η5-P5)2]; this is a new feature observed in the transition metals bound to cyclo-P5 ring. This finding is indeed supported by the indirect evidence observed by Scherer and coworkers from the diamagnetic behavior in an iridium derivative of Fe(P5), that the Fe atom is negatively charged while one of the P atoms is + charged