Trinuclear π-conjugated chromophores formed by a neutral ferrocenyl group and a cationic mixed ruthenium sandwich linked through an unsymmetrical Schiff-base complex spacer

The synthesis of neutral dinuclear unsymmetrical Schiff base complexes 1 and 2 was carried out in an one-pot two-step reaction sequence that involves the reaction of 1-ferrocenyl-1,3-butanedione with an excess of ethylenediamine in refluxing CH₂Cl₂, to generate the intermediate "half-unit" Fc-C(O)CH₂C(CH₃)=NCH ₂CH₂NH₂, Fc = (η⁵-Cp) Fe(η⁵-C₅H₄), Cp = C₅H ₅), followed by its in situ templated reaction with salicylaldehyde and nickel(II) or copper(II) acetate in refluxing CH₂Cl ₂-EtOH (3: 1) mixture. On the other hand, ionic trinuclear unsymmetrical complexes [3]⁺PF₆^- and [4] ⁺PF₆^- were synthesized by reacting dinuclear precursors 1 and 2, respectively, with [(η⁵-Cp*)Ru(CH ₃CN)₃]⁺PF₆^-, Cp* = C₅Me₅, in refluxing CH₂Cl₂. Both complexes contain the neutral electron-releasing ferrocenyl group and the cationic electron-withdrawal sandwich, [(η⁵-Cp*) Ru(η⁶-arene)]⁺, connected by a tetradentate {M(ONNO)} chelate (M = Ni, Cu). The new unsymmetrical organometallic Schiff base compounds were characterized by elemental analysis, IR, UV-Vis, ¹H NMR and EPR spectroscopy. In addition, the Ni(II) containing complexes 1 and [3] ⁺PF₆^- were authenticated by X-ray diffraction analysis. Solvatochromic and electrochemical properties were also studied. The organometallic-inorganic hybrid unsymmetrical Schiff base complexes [3] ⁺PF₆^- and [4]⁺PF₆ ^- can be defined as type I non-rod-shaped dipolar chromophores.