Abstract

New cationic organoiron(II) pyranylideneacetaldehyde hydrazone complexes were prepared in high yields through condensation reactions of the organometallic hydrazine precursor [CpFe(η6-p-MeC 6H4NHNH2)]+PF6 - with differently substituted α- and γ- pyranylideneacetaldehydes. The mononuclear hydrazones were stereoselectively obtained as their (E) isomers about the N=C double bond. All the new compounds were thoroughly characterized by a combination of elemental analysis and spectroscopic techniques (1H and 13C NMR, IR, and UV/Vis), and by a single-crystal X-ray diffraction analysis of the 2-tBu-chromene derivative 5. The spectroscopic data suggest that these complexes have a partial pyrylium character due to the electron-accepting ability of the cationic organometallic fragment and to the electron-releasing properties of the methylenepyran-based donor. The crystal structure of 5 shows that the η6-coordinated tolyl ring and the pyran ring are coplanar (dihedral angle 3.2°), a favorable situation that allows conjugation between the intracyclic oxygen atom and the cationic iron center through the entire hydrazone backbone. Compounds 4-6 are strongly polarized D-π-A systems that exhibit solvatochromic properties, low-lying intramolecular charge-transfer bands in their electronic absorption spectra, and enhanced second-order NLO properties (μβ), as measured by the EFISH technique at 1.907 μm. © Wiley-VCH Verlag GmbH & Co. KGaA, 2006.