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• One-pot three-component synthesis of chiral Cu(II)-N 2 O 2 Schiff base complexes. • D-π-A system built about a Cu-N 2 O 2 core derived from 1 R ,2 R -−−1,2-diaminocyclohexane. • X-ray crystal structure of the 3,5-difluorosubstituted Cu(II) derivatives. • Correlation between ferrocenyl redox potentials and second-order NLO responses. • Optimized geometries and electronic structures analysed by DFT and TDDFT calculation. The synthesis, spectroscopic and structural characterization, optical and electrochemical properties and theoretical studies of a family of four new copper(II) complexes supported by a ferrocene-containing N 2 O 2 -tetradentate chiral Schiff base ligand derived from enantiomerically pure (1 R ,2 R)-(−)-1,2-diaminocyclohexane are reported. The push-pull Cu(II) complexes were prepared following a one-pot three-component reaction involving the chiral half-unit (1 R ,2 R)-Fc-C(=O)CH C(CH 3)NH- c -C 6 H 10 NH 2, copper acetate monohydrate and the appropriately 3-R,5-R'-substituted salicylaldehyde derivative in a 1:1:1 ratio (Fc = ferrocenyl; 3 : R =H , R' = Cl; 4 : R =H , R' = Br; 5 : R =R' = F ; 6 : R =R' = NO 2), and isolated in 65–97% yields as brown microcrystalline products. The characterization of the synthesized compounds were investigated through CHN elemental analysis, UV–vis, FT-IR, high-resolution mass spectrometry, and X-ray diffraction analysis in the case of the difluoro substituted complex 5 that was obtained in the form of single crystals. It crystallizes in the orthorhombic non-centrosymmetric space group P 2 1 2 1 2 1 , with two (R,R)-(−)-chiral carbon atoms in the structure. The four-coordinate Cu(II) metal ion adopts a slightly distorted square planar geometry. Magnetic properties of powdered samples have been investigated (2-300 K) and found consistent with a single isolated copper(II) ion (s = 1/2). Cyclic voltammetry showed that the stronger the electron withdrawing effect of the 3,5-substituents, the more anodically shifted the oxidation potential (E 1/2) of the ferrocenyl moiety, following the order: 5-Cl < 5-Br < 3,5-F 2 < 3,5-(NO 2) 2. This trend is similar when considering the values of the second-order polarizabilities β of these compounds as measured using Harmonic Light Scattering (HLS) at 1.9 µm, confirming the increasing electron withdrawing effect evidenced by electrochemical studies as well as the conjugation between the electron donor ferrocenyl moiety and the different halogen or nitro substituents through the square planar copper Schiff base framework. Finally, DFT and TD-DFT calculations allow to rationalize the structure and properties of the complexes. [Display omitted] [ABSTRACT FROM AUTHOR]

The synthesis of neutral dinuclear iron-nickel unsymmetrical Schiff base complexes 3 and 4 was achieved via a template reaction involving equimolar amounts of alkyl or aryl 'half-unit' precursors, respectively, Fc-C(O)CH=C(CH)N(H)R ( 1: R = CHCHNH; 2: R = o-CHNH; Fc = CpFe(η-CH); Cp = η-CH), 5-bromosalicylaldehyde and nickel(II) acetate tetrahydrate in a refluxing CHCl/MeOH (1:1) mixture. The ionic trinuclear unsymmetrical complex 5 was prepared by reacting its dinuclear precursor 3 with the arenophile source, [Cp*Ru(NCCH)]PF (Cp* = η-C(CH)), in refluxing CHCl for 2 h, whereas the trinuclear species 6 was formed upon regioselective π-complexation of the 5-bromosalicylidene ring of 4 by [Cp*Ru] at room temperature overnight. All the new compounds were adequately characterized by analytical and spectroscopic techniques and, in addition, the crystal and molecular structures of the 'half-unit' 1, the binuclear complex 4 and its hemisolvate adduct 4 · 0.5CHOH, the trinuclear Schiff base compound 5 · 2(CH)CO, and the mixed sandwich metalloligand 7 have been determined by X-ray crystallography. Both organometallic-inorganic hybrids 5 and 6 contain the neutral electron-releasing ferrocenyl group, and the cationic electron-withdrawing ruthenium mixed sandwich, linked through the unsymmetrical tetradentate Schiff base complex {Ni(ONNO)}. UV-vis, H and C NMR as well as electrochemical data clearly indicate a mutual donor-acceptor electronic influence between the organometallic termini. Furthermore, X-ray crystal structure analysis of 5 · 2(CH)CO reveals the partial delocalization of bonding electron density throughout the dinucleating nickel Schiff base ligand. [ABSTRACT FROM AUTHOR]

Abstract: The homobimetallic hydrazone complex [CpFe(η6-p-CH3C6H4)NHN=C(C6H4-p-CH3)(η5-C5H4)FeCp]+PF6 – (2) (Cp=η5-C5H5) is stereoselectively formed by reaction of the organometallic hydrazine precursor [CpFe(η6-p-CH3C6H4–NHNH2)]+PF6 – with the sterically demanding p-toluoylferrocene CpFe(η5-C5H4)CO(C6H4-p-CH3) (1) in refluxing ethanol. Compound 2 has been fully characterized by IR, UV–vis, and 1H NMR spectroscopy, cyclic voltammetry and by an X-ray diffraction analysis. The most striking features of the crystal structure are the syn-conformation of the two organometallic units, the long Fe–C ipso bond distances and the slight cyclohexadienyl character at the coordinated C6 ring with a folding angle of 6.1°, and that coordinated C6- and C5-rings of the binucleating ligand are almost coplanar with a dihedral angle of 8.1°. The crystal structure of the p-toluoylferrocene 1 is also presented. To cite this article: W. Figueroa et al., C. R. Chimie 8 (2005) . [Copyright &y& Elsevier]

The stereoselective condensation reaction between organometallic hydrazine precursors [CpFe(η6-p-RC6H4&z.sbnd;NHNH2)]+PF6− (R=H, (1)+PF6−; Me, (2)+PF6−; MeO, (3)+PF6−; Cl, (4)+PF6−) and (E)-(2-ferrocenylvinyl)-methyl ketone, [(E)-[CpFe(η5-C5H4)&z.sbnd;CH&z.dbnd6;CH&z.sbnd;CO&z.sbnd;Me] (5), allowed the synthesis of a family of four new push–pull-type homodinuclear hydrazones complexes formulated as (E,E)-[CpFe(η6-p-RC6H4)&z.sbnd;NHN&z.dbnd6;CMe&z.sbnd;CH&z.dbnd6;CH&z.sbnd;(η5-C5H4)FeCp]+PF6− (R=H, (6)+PF6−; Me, (7)+PF6−; MeO, (8)+PF6−; Cl, (9)+PF6−). These compounds were fully characterized by a combination of elemental analysis and spectroscopic techniques (1H-NMR, IR and UV–Vis), and electrochemical studies in order to prove the π-donor–acceptor interactions between the two metallocenic termini through the asymmetric elongated π-conjugated spacer. Cyclic voltammetry studies reveal an electrochemically reversible one-electron oxidation and an irreversible one-electron reduction step for all the hydrazone derivatives. The redox potentials clearly indicate that the oxidation occurs at the ferrocenyl unit, and the reduction is localized on the mixed sandwich entity. In the electronic absorption spectra, two intense bands are observed in the visible region which undergo positive solvatochromic shifts. The origin of the high-energy absorption band is assumed to be an intraligand charge-transfer (ILCT) transition and the low-energy absorption band is assigned to a metal to ligand charge-transfer (MLCT) transition. Both ILCT and MLCT are shifted to lower energy with increasing spacer length. [Copyright &y& Elsevier]