Novel Cofacial Ruthenium(II) Porphyrin Dimers and Tetramers.

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.

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.

An in Situ X-ray Absorption Fine Structure Study of Different Oxidation States of Oxo- and Hydroxo-Bridged Ruthenium Dimers in Acetonitrile Solution.

X-ray absorption fine structure (XAFS) experiments have been performed in acetonitrile solution with an in situ electrochemical cell at controlled electric potentials on [Ru(2)(&mgr;-O) (&mgr;-CH(3)COO)(2)(bpy)(2)L(2)](n)()(+) (bpy = 2,2'-bipyridine; L = pyridine (1) and 1-methylimidazole (2)) with the formal ruthenium oxidation states Ru(II)Ru(III), Ru(III)Ru(III), and Ru(III)Ru(IV). Spectra were also recorded for the corresponding hydroxo-bridged species, abbreviated as Ru(II)Ru(II)H, Ru(II)Ru(III)H, and Ru(III)Ru(III)H, which were formed by addition of p-toluenesulfonic acid to 1 and 2 and subsequent electrolysis. The X-ray absorption near edge structure (XANES) spectra all showed similar features, although a small shift toward higher threshold energy was observed with increasing formal ruthenium oxidation state. It is concluded from the analysis of the EXAFS data that the ruthenium-ruthenium distance of the &mgr;-oxo complexes decreases with decreasing formal ruthenium oxidation state, interpreted as resulting from decreased electrostatic repulsion between the ruthenium atoms. However, for the &mgr;-hydroxo complexes the ruthenium-ruthenium distance decreases in the order Ru(III)Ru(III)H > Ru(II)Ru(II)H > Ru(II)Ru(III)H. The present coordination structures of the oxo- and hydroxo-bridged ruthenium dimers of the different oxidation states are compared with related iron and vanadium dimers.

Excitation energy flow control in {Ru(2,2'-bipyridine)2}-{pyridylporphyrin}2 systems.

The direction of excitation energy migration is reversed in a system composed of {Ru(bpy)(2)}-{pyridylporphyrin}(2) by the addition of a Zn(2+) ion. The Zn(2+) system shows an excitation-wavelength dependent emission.

Structural, redox, and photophysical studies of the tetra(pyridyl)porphyrin complex containing four (2,2'-bipyridine)(2,2':6',2"-terpyridine)ruthenium(II) groups.

New hybrid complexes of polypyridyl ruthenium and pyridylporphyrins have been prepared by the coordination of pyridyl nitrogens to the ruthenium centers. A 1:4 hybrid complex, [{Ru(bpy)(trpy)}4(mu4-H2Py4P)]8+ ([1]8+) (bpy = 2,2'-bipyridine; trpy = 2,2':6',2"-terpyridine; H2Py4P = 5,10,15,20-tetra(4-pyridyl)porphyrin), has been characterized by the single-crystal X-ray diffraction method. A 1:1 complex, [{Ru(bpy)(trpy)}(H2PyT3P)]2+ ([2]2+) (H2PyT3P = 5-(4-pyridyl)tritolylporphyrin) has also been prepared. The Soret band of the porphyrin ring shifts to longer wavelength with some broadening, the extent of the shift being larger for [1]8+. Cyclic voltammograms of the two complexes show simple overlap of the component redox waves. The complexes are weakly emissive at room temperature, which becomes stronger at lower temperatures. While [1]8+ at >140 K and [2]2+ at 77-280 K show only porphyrin fluorescence, [1]8+ at <140 K shows ruthenium and porphyrin phosphorescence, in addition to the porphyrin fluorescence.

Synthesis, properties, and crystal structure of a novel anthracene-bridged molybdenum-zinc porphyrin dimer.

The synthesis and properties of novel anthracene-bridged porphyrin dimers having an oxomolybdenum(V) porphyrin unit, H(2)(DPA)[Mo(V)O(OMe)] (1) and (DPA)[Mo(V)O(OMe)][Zn(II)(MeOH)] (2), and the relevant monomer porphyrin complexes Mo(V)O(MPP)OMe (3) and Zn(II)(MPP) (4) are presented. An oxomolybdenum(V) unit was introduced into one of the two porphyrins in DPA to give 1, which has a free-base porphyrin unit. By introducing a zinc(II) ion to the free-base part, a mixed-metal complex of 2 was prepared and isolated. The structure of 2 was analyzed by X-ray crystallography (2.(7)/(6)CH(2)Cl(2), triclinic, P(-)1 (no. 2), a = 15.2854(12) A, b = 19.9640(15) A, c = 13.6915(12) A, alpha = 90.968(3), beta = 113.108(4), gamma = 96.501(4), Z = 2, R1 = 9.9, wR2 = 19.2). The structure of 2 demonstrated that a methanol is stably coordinated to the Zn(II) ion with the aid of a hydrogen bond to the methoxo ligand on the Mo(V) ion in the binding pocket of DPA. The electrochemical measurements of 2 suggested that the methanol was kept in the pocket of DPA in solution even at the reduced state of the molybdenum ion.

Synthesis and properties of rhodium(III) porphyrin cyclic tetramer and cofacial dimer.

Rhodium(III) porphyrin complexes, [Rh(4-PyT(3)P)Cl](4) (1) and [Rh(2-PytB(3)P)Cl](2) (2) (4-PyT(3)P = 5-(4-pyridyl)-10,15,20-tritolylporphyrinato dianion, 2-PytB(3)P = 5-(2-pyridyl)-10,15,20-tri(4-tert-butyl)phenylporphyrinato dianion), were self-assembled and characterized by (1)H nuclear magnetic resonance spectroscopy, infrared spectroscopy, and electron spray ionization-mass spectroscopy methods. The spectroscopic results certified that the rhodium porphyrin complexes 1 and 2 have a cyclic tetrameric structure and a cofacial dimeric structure, respectively. The X-ray structure analysis of 1 confirmed the cyclic structure of the complex. The Soret bands of both oligomers were significantly broadened by excitonic interactions between the porphyrin units, compared to those observed for a corresponding analogue of Rh(TTP)(Py)Cl (TTP = 5,10,15,20-tetratolylporphyrinato dianion, Py = pyridine). Stepwise oxidation of the porphyrin rings in the oligomers was observed by cyclic voltammetry. The oligomers 1 and 2 are very stable in solution, and they slowly undergo reactions with pyridine to give corresponding monomer complexes only at high temperatures (approximately 80 degrees C).