Synthesis and properties of cyclic ruthenium(II) porphyrin tetramers

Tetrameric ruthenium(II) porphyrin complexes, [Ru(4-PyP3P)(CO)](4), 1, [Ru(4-PyT3P)(CO)](4), 2, and [Ru(4-PyT3P)(Py)](4), 3, (4-PyP3P = 5-(4-pyridyl)-10,15,20-triphenylporphyrinato dianion, 4-PyT3P = 5-(4-pyridyl)-10,15,20-tritolylporphyrinato dianion). were self-assembled and were characterized by H-1 NMR, IR, and FABMS spectroscopic methods and elemental analyses. The spectroscopic results certified that the ruthenium porphyrin complexes have cyclic tetrameric structures. UV-vis spectra of the tetramers showed broad Soret bands as compared with the respective monomer analogues of Ru(TPP)(CO)(Py) and Ru(TPP)(Py)(2). The tetramers 1-3 underwent reactions with a large amount of pyridine to give corresponding monomer complex. Sharpening and increasing intensity in the Soret bands, accompanied by the progress of the monomerization, indicated the presence of the excitonic interactions between cofacially arranged ruthenium porphyrin subunits in these tetrameric molecules. Electrochemical analyses revealed that the first ring-oxidation processes in 1 and 2, and the oxidation process of Ru(II) to Ru(III) in 3 proceed stepwise.