Organo-Iron Benzaldehyde-Hydrazone Complexes. Synthesis, Characterization, Electrochemical, and Structural Studies
2002; American Chemical Society; Volume: 22; Issue: 1 Linguagem: Inglês
10.1021/om020672t
ISSN1520-6041
AutoresCarolina Manzur, Lorena Millán, W. Figueroa, Daphne Boys, Jean‐René Hamon, David Carrillo,
Tópico(s)Organometallic Complex Synthesis and Catalysis
ResumoA series of new monocationic organo-iron(II) benzaldehyde-hydrazone complexes of general formula [CpFe(η6-o-RC6H4−NHNCH−C6H4-p-R')]+PF6- (Cp = η5-C5H5; R,R' = H, H 5; H, Me 6; H, MeO 7; H, NMe2 8; Me, Me 9; Me, MeO 10; Me, NMe2 11; MeO, Me 12; MeO, MeO 13; MeO, NMe2 14; Cl, Me 15; Cl, MeO 16; Cl, NMe2 17) have been synthesized. These mononuclear hydrazones were stereoselectively obtained as their trans-isomers about the NC double bond, by reaction of the corresponding organometallic hydrazine precursors [CpFe(η6-o-RC6H4−NHNH2)]+PF6- (R = H, 1; Me, 2; MeO, 3; Cl, 4) with p-substituted benzaldehydes p-R'C6H4CHO (R' = H, Me, MeO, NMe2) in refluxing ethanol. The N-methyl derivatives formulated as [CpFe{η6-C6H5−N(Me)NCH−C6H4-p-R'}]+PF6- (R' = Me, 18; MeO, 19; NMe2, 20) are readily prepared by deprotonation of complexes 6−8 with n-butyllithium and subsequent alkylation with iodomethane in THF at −70 °C. All these complexes have been fully characterized by elemental analysis, IR, UV−vis, and 1H NMR spectroscopies, and mass spectrometry for compounds 10, 12, and 16. Complexes 6 and 19 have also been characterized by single-crystal X-ray diffraction analysis. One of the more salient features of these structures is the long Fe−Cipso bond distances and the slight cyclohexadienyl character at the coordinated C6 ring with a folding angle of 6.2° and 7.4°, respectively. Moreover, the two phenyl rings of each compound are almost coplanar with a dihedral angle of 4.9° for 6 and 6.2° for 19. Cyclic voltammetry of the benzaldehyde-hydrazone complexes 5−8, 11, 14, and 17 in DMF shows an irreversible reduction wave at ca. −1.92 V vs Ag/AgCl, depending on the nature of both R and p-R' substituents, corresponding to the reduction of an in situ generated zwitterionic Fe(II) intermediate. The irreversible reduction waves of the cationic N-methylated hydrazones 18−20 are observed in the expected range −1.35 to −1.47 V vs Ag/AgCl, either in DMF or in acetonitrile.
Referência(s)