Organometallic phthalazin-1(2H)-ones: Electrochemistry and advantage of solvothermal synthesis

Abstract o-Ferrocenylcarbonylbenzoic acid (η5-C5H5)Fe(η5-C5H4C(O)C6H4COOH) (I) and o-cymantrenylcarbonylbenzoic acid (II) were obtained from ferrocene or (η5-C5H5)Mn(CO)3, respectively, by the Friedel–Crafts reaction with phthalic anhydride. Methyl o-ferrocenylcarbonylbenzoate (η5-C5H5)Fe(η5-C5H4C(O)C6H4COOMe (III) and methyl o-cymantrenylcarbonylbenzoate (CO)3Mn(η5-C5H4C(O)C6H4COOMe) (IV) were synthesized from I and II, respectively using dimethyl carbonate (DMC) in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) to promote the methylation reaction. 4-Ferrocenylphthalazin-1(2H)-one (V) and 4-cymantrenylphthalazin-1(2H)-one (VI) were obtained by the interaction of hydrazine hydrate with I and II, respectively, by the prolonged reflux or convenient solvothermal synthesis. Cyclic voltammetry measurements showed that compounds III and V undergo reversible one-electron oxidation, localized presumably at the ferrocene unit. For III the irreversible one-electron oxidation is apparently associated with the oxidation of the benzoate fragment. All new compounds were characterized by spectroscopic methods and the molecular structures of II and III were determined by X-ray diffraction analysis.