PERPENDICULARLY ARRANGED RUTHENIUM PORPHYRIN DIMERS AND TRIMERS

A series of ruthenium(II) porphyrin dimers and trimers (carbonyl dimer s, 1-4; carbonyl trimers, 5-7, bis(pyridyl) trimers, 8-10), having axi al or bridging porphyrin ligands, were synthesized and characterized b y H-1 NMR and IR spectroscopy and mass spectrometry. An X-ray structur al determination of Ru-II(OEP)(CO)(H(2)PyP(3)P) (1) (OEP = octaethylpo rphyrinato dianion, H(2)PyP(3)P = 5-pyridyl-10,15,20-triphenylporphyri nato dianion) was carried out. The axial porphyrin ligand is coordinat ed to the ruthenium porphyrin subunit obliquely. The Ru-N(Py) bond len gth is 2.237(4) Angstrom, and the angle between the ruthenium porphyri n macrocycle and the pyridyl ring is 63.23(35)degrees. Crystallographi c data for 1 are as follows: chemical formula C80H73N9ORu . CH2Cl2, tr iclinic, <P(1)over bar>, a = 14.954(5) Angstrom, b = 25.792(5) Angstro m, c = 10.124(3) Angstrom, alpha = 90.21(2)degrees, beta = 108.33(2)de grees, gamma = 73.39(2)degrees, Z = 2, R(F) = 0.0674. H-1 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 su bunits through the pyridyl group in solution. UV-vis spectra revealed the presence of excitonic interaction between two axial ligand porphyr in subunits in the trimers 8-10. The MLCT bands from the central ruthe nium(II) ions to the octaethylporphyrin rings were observed around 450 nm in 8 and 9. Cyclic voltammograms of the carbonyl dimers and trimer s showed no redox waves of the ruthenium(II) ions, because the rutheni um(II) oxidation state of these complexes was significantly stabilized by the coordination of the axial CO ligands. On the other hand, bis(p yridyl) trimers exhibit the Ru(III/II) waves in the region of -0.12 to +0.15 V vs Ag/Ag+ reference electrode.