Orthogonal Ru II(bpy) 3 complexes in meso-substituted porphyrins

Abstract

The synthesis and characterization of mono- and bis- meso-substituted porphyrins, where the substituents are bipyridine (bpy) groups are described. Treatment of these new porphyrins with an excess of cis-RuCl 2(bpy) 2 gives rise to their respective mono- and bis-Ru II(bpy) 3 complexes. These ruthenium porphyrin complexes all exist as a number of structural isomers and this is reflected in both the proton and carbon NMR spectra. The cyclic voltammetry of these redox active systems was examined and is reported herein. The cyclic voltammetry for the ruthenium porphyrins is complex, with the usual two oxidation and two reduction waves of porphyrins mixing with the three reduction waves of the porphyrin bound Ru II(bpy) 3 and the single oxidation wave seen for the Ru II/Ru III couple. In the case of the mono-ruthenium porphyrin, this complex redox chemistry results in the presence of a reversible two-electron reduction, along with the other redox processes. The bis-ruthenium porphyrin has an even more complex redox chemistry. However, the first ligand-based reduction wave in both the mono- and bis-substituted complexes, occur at more negative potentials than those in, simple free, Ru II(bpy) 3.