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.