Perpendicularly Arranged Ruthenium Porphyrin Dimers and Trimers

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.