Organodiiron(II)-complexes containing a long conjugated hydrazonato spacer. Synthesis, characterization, electrochemical and structural studies

Organometallic hydrazines of general formula [(η5-Cp)Fe(η6-p-RC6H4NHNH2)]+PF6− (Cp=C5H5; R=H, (1)+PF6−; Me, (2)+PF6−; MeO, (3)+PF6−; Cl, (4)+PF6−) react with equimolar quantities of (E)-4-(2-ferrocenylvinyl)-benzaldehyde, (E)-[(η5-Cp)Fe(η5-C5H4)CHCHC6H4CHO], to afford stereoselectively, the new homodimetallic hydrazones formulated as (E)-[(η5-Cp)Fe(η6-p-RC6H4)NHNCHC6H4CHCH(η5-C5H4)Fe(η5-Cp)]+PF6− (R=H, (5)+PF6−; Me, (6)+PF6−; MeO, (7)+PF6−; Cl, (8)+PF6−). These compounds were fully characterized by elemental analysis and spectroscopic techniques (1H- and 13C-NMR, IR and UV–vis) and, in the case of complex (6)+PF6−, by single crystal X-ray diffraction methods. The rotations of the ferrocenyl unit by 37.2° out of the NHNCHC6H4CHCH spacer and coordinated phenyl ring planes, may generate an unfavorable structure to allow π-electron delocalization along the entire hydrazonato backbone between the two metals separated through bonds by more than 1.8 nm, as confirmed by the electrochemical data.