A series of ruthenium(II) porphyrin dimers and trimers (carbonyl dimers, 1-4; carbonyl trimers, 5-7, bis(pyridyl) trimers, 8-10), having axial or bridging porphyrin ligands, were synthesized and characterized by (1)H NMR and IR spectroscopy and mass spectrometry. An X-ray structural determination of Ru(II)(OEP)(CO)(H(2)PyP(3)P) (1) (OEP = octaethylporphyrinato dianion, H(2)PyP(3)P = 5-pyridyl-10,15,20-triphenylporphyrinato dianion) was carried out. The axial porphyrin ligand is coordinated to the ruthenium porphyrin subunit obliquely. The Ru-N(Py) bond length is 2.237(4) Å, and the angle between the ruthenium porphyrin macrocycle and the pyridyl ring is 63.23(35) degrees. Crystallographic data for 1 are as follows: chemical formula C(80)H(73)N(9)ORu.CH(2)Cl(2), triclinic, P&onemacr;, a = 14.954(5) Å, b = 25.792(5) Å, c = 10.124(3) Å, alpha = 90.21(2) degrees, beta = 108.43(2) degrees, gamma = 73.39(2) degrees, Z = 2, R(F) = 0.0674. (1)H NMR signals of 2,6- and 3,5-pyridyl protons of the axial ligand porphyrins of the oligomers 1-10 showed significant upfield shifts, indicating that the axial porphyrin subunits are coordinated to the ruthenium porphyrin subunits through the pyridyl group in solution. UV-vis spectra revealed the presence of excitonic interaction between two axial ligand porphyrin subunits in the trimers 8-10. The MLCT bands from the central ruthenium(II) ions to the octaethylporphyrin rings were observed around 450 nm in 8 and 9. Cyclic voltammograms of the carbonyl dimers and trimers showed no redox waves of the ruthenium(II) ions, because the ruthenium(II) oxidation state of these complexes was significantly stabilized by the coordination of the axial CO ligands. On the other hand, bis(pyridyl) trimers exhibit the Ru(III/II) waves in the region of -0.12 to +0.15 V vs Ag/Ag(+) reference electrode.

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 1H 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 complexes. 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.

A series of cofacially arranged ruthenium(II) porphyrin dimers 1-5 having a variety of axial ligands such as CO, pyridine, and 4-cyanopyridine, were synthesized. Porphyrin tetramers, 6 and 7, which have pyridylporphyrin ligands at the axial positions of the parent cofacial ruthenium(II) dimers, were also prepared. These porphyrin dimers and tetramers were characterized by (1)H NMR spectroscopy, ESI (electrospray ionization)-mass spectroscopy, and elemental analysis. The ruthenium porphyrin dimers and tetramers exhibited characteristic electrochemical and spectroscopic properties caused by interactions between the porphyrin subunits. Stepwise oxidations of the porphyrin rings or the ruthenium ions in the cofacial dimer skeltons were observed in the cyclic voltammograms. The potential differences (DeltaE degrees ' mV) of the oxidation steps were larger than 260 mV for all the porphyrin oligomers. The Soret bands of the cofacial dimers were significantly broadened by excitonic interactions between the two porphyrin subunits. Furthermore, the mixed-valence states of 3-7 showed specific intervalence charge-transfer (IT) bands between the Ru(II) and Ru(III) cores in the near-IR region at around 1500 nm.