Method for the Synthesis of Ferrocenylhydrazine and Its Properties and Reactivity

The reaction of iodoferrocene (FcI) with tert-butyl or benzyl carbazate gives the protected ferrocenylhydrazines tert-butyl-1-ferrocenylhydrazine-1-carboxylate (1) and benzyl-1-ferrocenylhydrazine-1-carboxylate (2). Air-stable 2was converted to ferrocenylhydrazine (3) by Pd-catalyzed hydrogenolysis under mild conditions in yields of up to 70% (based on the starting FcI). The applicability of 3in the synthesis of heterocycles bearing a Fc–N–N fragment was demonstrated by the preparation of (3,5-dimethylpyrazol-1-yl) ferrrocene (4), (3-trifluoromethyl-5-phenyl-pyrazol-1-yl) ferrrocene (5), (1,2,4-diazaphosphol-1-yl) ferrrocene (6), (1,2,4-diazarsol-1-yl) ferrrocene (7), and 1-ferrocenyl-4,5-dichloro-pyridazin-6-one (8). Condensation of 3with FcCH═O yielded bimetallic ferrocene carboxaldehyde ferrocenylhydrazone (9). Electrochemical studies on this series of ferrocenylated compounds showed that both the hydrazine and protected hydrazine function serve as electron donors, whereas N-bonded heterocycles possess weak electron-withdrawing properties. All compounds studied have been fully characterized by spectroscopic methods and their molecular structures are reported.