Domain: Coordination chemistry

A coordination complex of iron, $(\eta^5\text{-Cp})\mathrm{Fe}(\mathrm{CO})_2\mathrm{Cl}$, is treated with one equivalent of sodium cyclopentadienide ($\mathrm{NaCp}$) in a tetrahydrofuran (THF) solution. The reaction proceeds with the quantitative elimination of sodium chloride ($\mathrm{NaCl}$). Determine the structural formula of the resulting product complex, accurately representing all ligands and binding modes.

Grading rubric:
criterion: The solution explicitly identifies the $\mathrm{Fe}$ center as the electrophilic target due to the $\pi$-acidic nature of the $\mathrm{CO}$ ligands.
weight: 20
criterion: The solution explicitly attributes the reaction's thermodynamic drive to the lattice energy release associated with $\mathrm{NaCl}$ precipitation.
weight: 10
criterion: The solution establishes that the starting material is an 18-electron complex with $\mathrm{Fe}$ in the $+2$ oxidation state.
weight: 10
criterion: The solution explicitly notes that the $\mathrm{Fe(II)}$ oxidation state is retained in the final product, owing to a lack of redox reagents.
weight: 10
criterion: The solution correctly sums the electrons for the $(\eta^5\text{-Cp})\mathrm{Fe}(\mathrm{CO})_2$ fragment to reach $16~e^-$.
weight: 20
criterion: The solution explicitly states that $\eta^5/\eta^5$ coordination is forbidden because it would populate anti-bonding molecular orbitals ($22~e^-$ count).
weight: 10
criterion: The solution explicitly notes that $\eta^3$-coordination is rejected because it would lead to an unstable 20-electron configuration.
weight: 10
criterion: The solution provides the correct structural formula as exactly $(\eta^5\text{-Cp})\mathrm{Fe}(\mathrm{CO})_2(\eta^1\text{-Cp})$.
weight: 10

Answer:
(η^5-Cp)Fe(CO)2(η^1-Cp)