Synthesis and characterization of mono- and dinuclear phenanthroline-extended tetramesitylporphyrin complexes as well as UV-Vis and EPR studies on their one-electron reduced species

Abstract

The syntheses of mononuclear compounds based on the fused porphyrin phenanthroline ligand (H₂2-1) and their corresponding dinuclear porphyrin bis-bipyridine ruthenium complexes are reported. The extended π-system of the ligand is able to store electron equivalents as could be proven by the single electron reduction with KC₈ (and/or Na(Hg)) followed by subsequent UV-Vis and EPR analysis. Electron reduction could also be achieved under light illumination in a dichloromethane–triethylamine mixture. The two coordination spheres of the ligand are different so that mononuclear or (hetero)dinuclear complexes can be isolated depending on the reaction conditions. We could successfully introduce Zn, Cu and Pd into the porphyrinic unit leading to a series of mononuclear (M-1) compounds. Further, we could attach the bis-(4,4′-di-tert-butyl-2,2′-bipyridine) ruthenium fragment (Ru(tbbpy)₂²⁺) to obtain dinuclear (M-1-Ru) metal complexes. In the case of Zn-1 an X-ray crystal structure could be obtained confirming the selective metallation in the porphyrinic unit. All metal complexes were isolated and characterized with standard analytical tools (elemental analysis, mass spectrometry and NMR (or EPR) spectroscopy).