Coordinated Hydrazone Ligands as Nucleophiles:  Reactions of Fe(papy)₂

The diamagnetic iron(II) complexes of the hydrazone ligand pyridinecarboxaldehyde-2‘-pyridylhydrazone (papyH) have been characterized by NMR, IR, UV−vis, and electrochemistry. The dication Fe(papyH)₂²⁺ undergoes reversible one-electron oxidation at 0.66 V vs internal ferrocene and shows a strong metal−ligand charge-transfer band in the visible region at 524 nm. Deprotonation with NaOH gives diamagnetic, neutral Fe(papy)₂ with an oxidation potential of −0.25 V vs internal ferrocene and a charge-transfer band at 603 nm. Fe(papy)₂ reacts with active alkylating agents to give dialkyl complexes Fe(papyR)₂²⁺ with spectroscopic properties similar to those of Fe(papyH)₂²⁺. Monitoring the alkylation by UV−vis reveals the intermediacy of a monoalkylated species.