Transition metal complexes of the novel hexadentate ligand 1,4-bis(di(N-methylimidazol-2-yl)methyl)phthalazine

Abstract

The novel polydentate ligand 1,4-bis(di(N-methylimidazol-2-yl)methyl)phthalazine, bimptz, has been synthesized and its coordination chemistry was investigated. Bimptz is neutral and contains a central phthalazine unit, to which two di-(N-methylimidazol-2-yl)methyl groups are attached in the 1,4-positions. This ligand therefore provides up to 6 donor sites for coordination to metal ions. A series of metal complexes of bimptz was prepared and their molecular structures were determined by X-ray diffraction. Upon reaction of bimptz with two equivalents of MnCl₂·4H₂O, CoCl₂·6H₂O and [Ru(dmso)₄Cl₂], the dinuclear complexes [Mn₂(bimptz)(µ-Cl)₂Cl₂] (1), [Co₂(bimptz)(CH₃OH)₂(µ-Cl)₂](PF₆)₂ (3) and [Ru₂(bimptz)(dmso)₂(µ-Cl)₂](PF₆)₂ (4), respectively, were isolated. The latter were found to have similar solid state structures with octahedrally coordinated metal centers bridged by the phthalazine unit and two chloro ligands. The cobalt and ruthenium complexes 3 and 4 were isolated as PF₆⁻ salts and contain neutral methanol and dmso ligands, respectively, at the terminal coordination sites of the metal centres. The mononuclear ruthenium complex [Ru(Hbimptz)₂](PF₆)₄ (6) was obtained from the reaction of two equivalents bimptz with [Ru(dmso)₄Cl₂]. In complex 6, three donor sites per ligand molecule are used for coordination of the Ru(II) center. In each bimptz ligand, one of the remaining, dangling N-methylimidazole rings is protonated and forms a hydrogen bond with the unprotonated N-methylimidazole ring of the other bimptz ligand.