A Ruthenium(II) Complex with a Tripodal Ligand Containing Three Imidazole Groups

The orange [Ru II (H 3 L)](ClO 4 ) 2 · 3H 2 O ( 1 ) complex was synthesized from cis ‐[RuCl 2 (dmso) 4 ] and H 3 L, where H 3 L (tris{[2‐{(imidazol‐4‐yl)methylidene}amino]ethyl}amine) is a tripodal ligand obtained by condensation of tris(2‐aminoethyl)amine and 4‐formylimidazole in a 1:3 mol ratio. The X‐ray crystal structure analysis revealed that the complex has an octahedral structure coordinated by three imidazole nitrogen atoms and three Schiff base (imine) nitrogen atoms. The uncoordinated NH groups of the imidazole moieties of 1 are easily deprotonated by the action of a base. The effect of deprotonation on the Ru III /Ru II redox potential was studied by cyclic voltammetry in methanol containing 0.1 M LiClO 4 . Complete deprotonation shifts the Ru III /Ru II potential to a much more negative value from –0.18 to –0.72 V vs. Ag/Ag + , making it easier to oxidize. The bluish‐purple Ru III complex, [Ru III (H 3 L)] 3+ , was formed by controlled‐potential electrolysis of 1 , and the electronic spectrum is reported. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)