Preparation, characterization and electrochemical and X-ray structural studies of new conjugated 1,1′-ferrocenediyl-ended [CpFe-arylhydrazone]+salts

Abstract

A series of new conjugated bimetallic ferrocenyl 1,1′-bis-substituted compounds of the type (E)-[CpFe(η6-p-RC6H4)NHNCH(η5-C5H4)Fe(η5-C5H4)–CHCHC6H4-p-R′]+PF6− (Cp = η5-C5H5; R, R′ = H, NO2, 11; Me, NO2, 12; MeO, NO2, 13; Cl, NO2, 14; Me, CN, 15; Me, Me, 16), with end-capped (E)-ethenylaryl and [CpFe(arylhydrazone)]+ substituents, have been prepared by the condensation reaction of 1,1′-(p-R′-arylethenyl)ferrocenecarboxaldehyde (R′ = Me, 4; NO2, 5; CN, 6) with the organometallic hydrazine precursors [CpFe(η6-p-RC6H4NHNH2)]+PF6− (R = H, 7; Me, 8; MeO, 9; Cl, 10). In the trimetallic series, {[CpFe(η6-p-RC6H4)NHNCH(η5-C5H4)]2Fe}2+[PF6−]2 (R = H, 17; Me, 18; MeO, 19, Cl, 20), which results from the condensation of two equivalents of the same organometallic hydrazine precursor (7–10) with 1,1′-ferrocenedicarboxaldehyde, the ferrocenediyl core symmetrically links two cationic mixed-sandwich units. These ten hydrazones (11–20) were stereoselectively obtained as their trans isomers about the NC double bond. All the new compounds were thoroughly characterized by a combination of elemental analysis, spectroscopic techniques (1H NMR, IR and UV-Vis) and electrochemical studies in order to prove electronic interaction between the donating and accepting units through the π-conjugated system. A representative example of each series has also been characterized by single crystal X-ray diffraction analysis. The bimetallic complex 16+ adopts an anti conformation with the two iron atoms on opposite faces of the dinucleating hydrazonato ligand, whereas the trinuclear complex 192+ adopts a syn conformation with an Fe–Fe–Fe angle of 180°. Other salient features of these structures are the long Fe–Cipso bond distances and the slight cyclohexadienyl character at the coordinated C6 ring, with a folding angle of 7.4° and 7.0° for 16+ and 192+, respectively.