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)(2)(2+) 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)(2)(2+) with spectroscopic properties similar to those of Fe(papyH)(2)(2+). Monitoring the alkylation by UV-vis reveals the intermediacy of a monoalkylated species.