A bis 1,10-phenanthroline ligand leading to octahedral Ru(II) complexes containing a well-defined axis

A bis-chelating ligand (1), made of two 1,10-phenanthroline subunits connected with a p-(CH₂)₂C₆H₄(CH₂)₂- spacer through their 4 positions, has been prepared, using Skraup syntheses and reaction of the anion of 4-methyl-7-anisyl-1,10-phenanthroline with α,α’-dibromo-p-xylene. Complexation of 1 with Ru(CH₃CN)₄Cl₂ and subsequent reaction with 4,4’-dimethyl-2,2’-bipyridine afforded an octahedral Ru(II) tris-diimine complex, in which a well-defined axis running through the terminal anisyl substituents and the central metal has been created, as shown by an X-ray molecular structure analysis.     

2,9-Di-(2'-pyridyl)-1,10-phenanthroline: a tetradentate ligand for Ru(II)

The tetradentate ligand 2,9-di-(2'-pyridyl)-1,10-phenanthroline is synthesized in 62% yield by the Stille coupling of 2,9-dichloro-1,10-phenanthroline and 2-(tri-n-butylstannyl)pyridine. Treatment of this ligand with RuCl3.3H2O and a 4-substituted pyridine results in the formation of a complex in which the tetradentate ligand occupies the equatorial plane and two pyridines are bound axially. The interior N-Ru-N angles vary from 76.1 degrees to 125.6 degrees , showing considerable distortion from the 90 degrees ideal. The lowest energy electronic transition is sensitive to the electronegativity of the 4-substituent on the axial pyridines, varying from 516 nm for the CF3 group to 580 nm for the NMe2. The oxidation potentials mirror this trend, spanning a range of 1.36-1.03 V, while the reduction potentials show less variation (-0.97 to -1.08 V). The complexes are nonemissive, presumably due to competitive nonradiative processes caused by distortion of the system.     

Iron(II) and nickel(II) mixed-ligand complexes containing 1,10-phenanthroline and 4,7-diphenyl-1,10-phenanthroline

Two types of mixed-ligand complexes, i.e. [M(phen)2 (dip)]2+ and [M(phen)(dip)2]2+ (M = iron(II) and nickel(II); phen = 1,10-phenanthroline and dip = 4,7-diphenyl-1,10-phenanthroline) have been prepared from their related tris-complexes, [M(phen)3]2+ by ligand substitution, and isolated by semi-preparative HPLC. Elemental and chromatographic analyses confirm the purity of the isolated complexes while u.v./vis and i.r. spectra were used to identify and characterize them. 1H-n.m.r. and room temperature Mössbauer spectra of the iron(III) complexes were also measured and the results are discussed. In addition, our preliminary results on hypochromicity in the MLCT band and circular dihroism (CD) emerging in the u.v./vis region upon addition of CT(calf thymus)-DNA to the racemic complexes indicated that the iron(II) mixed-ligand complexes interact with CT-DNA.     

Redox properties of bis(1,10-phenanthroline)-(pyridine)ruthenium(II) complexes

The redox properties of a series of [Ru(phen)₂(py)X]ⁿ⁺ cations (X = pyridine, NH₃, Cl, Br, I, CN, SCN, N₃ and NO₂) have been investigated in acctonitrile. Two reversible reduction steps are seen at ? 1.35 and ? 1.6 V vs Ag/AgCl; the invariance of these processes with X-group is indicative of electron addition to molecular orbitals mainly of phenanthroline ligand π^* origin. Irreversible multi-electron reductions follow below ? 2.20 V. The Ru(II)/Ru(III) couple is seen as a reversible wave near + 0.8 V vs the normal hydrogen electrode, from calibration with ferrocene, except in the cases of the NO₂ and SCN complexes, where rapid reactions involving these ligands occur.     

ESI-MS studies of mixed-ligand Fe(II) complexes containing 1,10-phenanthroline and 1,10-phenanthroline-5,6-dione as ligands

In order to monitor the progression of the synthesis and the separation of novel mixed-ligand iron complexes containing 1,10-phenanthroline, 1,10-phenanthroline-5,6-dione, and NCS- as ligands all products were mass analyzed by electrospray ionization ion trap MS/MS. The spectra of methanol (MeOH), acetonitrile (ACN), water, and ethanol (EtOH) solutions were collected and the results were compared. It was detected under applied electrospray ionization mass spectrometry (ESI-MS) conditions that MeOH, water, and EtOH formed solvent clusters around the free or complexed 1,10-phenanthroline-5,6-dione. Owing to the solvent-ligand hydrogen-bond formation, the solvent-ligand clusters were formed in the polar protic solvents. The number of protic solvent molecules per complex ion in cluster depended on the number of 1,10-phenanthroline-5,6-dione ligands in the complex ion. Unlike MeOH, EtOH, or water, ACN was not involved in the formation of the solvent clusters with the iron complexes containing 1,10-phenanthroline-5,6-dione as ligand. We also showed that the NCS- group under certain solvent conditions served as a bidentate ligand.     

Synthesis, structure, and substitution mechanism of new Ru(II) complexes containing 1,4,7-trithiacyclononane and 1,10-phenanthroline ligands

Two new Ru complexes containing the 1,10-phenanthroline (phen) and 1,4,7-trithiacyclononane ([9]aneS3, SCH2CH2SCH2CH2SCH2CH2) ligands of general formula [Ru(phen)(L)([9]aneS3)]2+ (L = MeCN, 3; L = pyridine (py), 4) have been prepared and thoroughly characterized. Structural characterization in the solid state has been performed by means of X-ray diffraction analyses, which show a distorted octahedral environment for a diamagnetic d6 Ru(II), as expected. 1H NMR spectroscopy provides evidence that the same structural arrangement is maintained in solution. Further spectroscopic characterization has been carried out by UV-vis spectroscopy where the higher acceptor capability of MeCN versus the py ligand is manifested in a 9-15-nm blue shift in its MLCT bands. The E1/2 redox potential of the Ru(III)/Ru(II) couple for 3 is anodically shifted with respect to its Ru-py analogue, 4, by 60 mV, which is also in agreement with a higher electron-withdrawing capacity of the former. The mechanism for the reaction Ru-py + MeCN--> Ru-MeCN + py has also been investigated at different temperatures with and without irradiation. In the absence of irradiation at 326 K, the thermal process gives kinetic constants of k2 = 1.4 x 10(-5) s(-1) (DeltaH(++) = 108 +/- 3 kJ mol(-1), DeltaS(++) = -8 +/- 9 J K(-1) mol(-1)) and k-2 = 2.9 x 10(-6) s(-1) (DeltaH(++) = 121 +/- 1 kJ mol(-1), DeltaS(++) = 18 +/- 3 J K(-1) mol(-1)). The phototriggered process is faster and consists of preequilibrium formation of an intermediate that thermally decays to the final Ru-MeCN complex with an apparent rate constant of (k1Khnu)app = 1.8 x 10(-4) s(-1) at 304 K, under the continuous irradiation experimental conditions used.     

Low Valence States of Metal Chelates. V. Tris(1,10-phenanthroline)cobalt(II) and bis(2,9-dimethyl-1,10-phenanthroline)cobalt(II) perchlorates

D. C. polarography and cyclic voltammetry were used for investigating the reduction processes of the tris(1,10-phenanthroline)cobalt(II) and bis(2,9-dimethyl-1, 10-phenanthroline)-cobalt(II) perchlorates in 0.1 M solutions of tetraethylammonium perchlorate in acetonitrile. The first complex gave a four-step reduction wave; the first two steps were found to be diffusion controlled and reversible reductions from Co(phen)⁺ to Co(phen)₃⁺ to Co(phen) to Co(phen;) occured. The second complex gave a six-step reduction wave; the first three steps were found to be diffusion controlled and were to be considered as successive reversible reductions from Co(2, 9dm-phen)⁺ to Co(2, 9dmphen), from Co(2, 9dmphen) to Co(2, 9dmphen)₂ and from Co(2, 9dmphen)₂ to Co(2, 9dmphen).     

Isomerization of DNA-bound distilbazolium ligand induced by electron transfer from photoexcited tris(1,10-phenanthroline)Ru(II)

The ability of the DNA duplex to behave as an efficient organized medium for cis-trans isomerization induced by electron transfer (ET) has been explored. Isomerization studies, luminescence quenching and DNA photocleavage assays show that photoexcited Ru(1,10-phenanthroline [phen])3(2+) transfers an electron to E,Z1,4-bis[2-(1-methylpyridinium-4-yl)vinyl]benzene (E,Z pMPVB), which subsequently undergoes one-way isomerization to E,E pMPVB. The unusual feature of the system is manifested by the lack of friction that is usually imposed on the photoisomerizable ligand by highly organized media. The apparent rate of ET in DNA increases when compared with the homogeneous solution. However, after correction for the local concentration of the reagents onto the biopolymer, the rate constant becomes independent of the DNA concentration and is at least 4 x 10(2) times smaller than that in the homogeneous aqueous solution. Using the photoinduced isomerization system, a large enhancement in the efficiency of single-strand break formation was found in plasmid DNA over that for Ru(phen)3(+2) alone using irradiation at lambda > 480 nm.     

Ethylenediamine and 1,10-phenanthroline biscyclometallated complexes of Pd(II) and Pt(II) based on 4,6-diphenylpyrimidine

Biscyclometallated [(M(N∧N))₂(μ-dphpm)](ClO₄)₂ and [(N∧N)Pd(μ-dphpm)Pt(N∧N)]Cl₂ complexes [M = Pd(II), Pt(II); (N∧N) ethylenediamine (En), 1,10-phenanthroline (phen); dphpm² — bisdeprotonated form of 4,6-diphenylpyrimidine)] have been characterized by the ¹H NMR, electronic absorption and emission spectroscopy, and also cyclic voltammetry methods. The lowest unoccupied molecular orbital (LUMO) of biscyclometallated complexes with ethylenediamine, responsible for low-energy photo- and electro-stimulated processes irrespective of the metal nature, is assigned to the π* orbital mainly localized on the pyrimidine part of the bridging ligand. In the case of complexes with phenanthroline chelating ligands, the replacement of one or two palladium metal centers [{Pd(phen)}₂(μ-dphpm)]²⁺ by platinum centers changes the LUMO nature of the complexes for the π* orbital mainly localized on the peripheral metal-complex fragment {Pt(phen)}.     

Reversed-phase liquid chromatographic separation of Fe(II) and Fe(III) as their respective 1,10-phenanthroline and 5-sulphosalicylate complexes

A method has been developed for the separation of Fe(II)-1,10-phenanthroline and Fe(III)-5-sulphosalicylate complexes on a reversed-phase C₁₈ column in the presence of an ion-pairing reagent. Samples were injected on the column in the pre-complexed form and separated using a mobile phase consisting of acetonitrile [0.1% (w/v) in 5-sulphosalicylic acid] ?0.02 M sodium acetate buffer (pH 6.9) [0.1% (w/v) in tetramethylammonium chloride] (1 + 1). Spectrophotometric detection of the complexes was carried out at 515 nm. Linear calibration graphs were obtained for 1–12 μg mol^?1 Fe(II) and Fe(III).     

Ru(II) complexes of tetradentate ligands related to 2,9-di(pyrid-2'-yl)-1,10-phenanthroline

A series of 1,10-phenanthrolines were prepared having additional ligating substituents at the 2,9-positions. These substituents were either a 4-substituted pyrid-2-yl, quinolin-2-yl, 1,8-naphthyrid-2-yl, N-methyl imidazo-2-yl, or N-methyl benzimidazo-2-yl group. Additionally, 3,6-di-(pyrid-2'-yl)-dipyrido[3,2-a:2',3'-c]phenazine was prepared. All but two of these ligands coordinated Ru(II) in a tetradentate equatorial fashion with two 4-methylpyridines bound in the axial sites. An X-ray structure analysis of the diimidazoyl system indicates considerable distortion from square planar geometry in the equatorial plane. Previously reported variations in the axial ligand for such complexes appear to have a stronger effect on the electronic absorption and redox properties of the system than similar changes in the equatorial ligand. In the presence of excess Ce(IV) as a sacrificial oxidant at pH 1, all the systems examined catalyze the decomposition of water to generate oxygen. Turnover numbers are modest, ranging from 146 to 416.     

Bi-1,10-phenanthrolines and their mononuclear Ru(II) complexes

A series of four biphen (phen = 1,10-phenanthroline) ligands, 2,2'-biphen (1), 3,3'-biphen (2), 2,2'-dimethylene-3,3'-biphen (3), and 2,3'-dimethylene-3,2'-biphen (4), is prepared by coupling and Friedl?nder methodology. The corresponding mononuclear Ru(II) complexes, [Ru(1-4)(Mebpy)(2)](2+) where Mebpy = 4,4'-dimethyl-2,2'-bipyridine, are prepared. These complexes show long wavelength electronic absorptions at 441-452 nm and emissions at 622-641 nm. Metal-based oxidations occur in the range 1.18-1.21 V, and ligand-based reductions, at -1.20 to -1.30 V. The addition of Zn(2+), Cd(2+), or Hg(2+) ions results in a strong enhancement and red shift of the luminescence of complex Ru-3. Alkali and alkaline earth metal ions barely affect the luminescence of Ru-3 while transition metal ions such as Co(2+), Cu(2+), Ni(2+), and Mn(2+) lead to efficient quenching of the Ru-3 luminescence. The luminescence of Ru-2 and Ru-4 is quenched in the presence of Zn(2+) because of a conformationally induced reduction in electronic communication between the two phen halves of the ligand. The addition of Zn(2+) has only a slight effect on the luminescence of Ru-1 because of steric hindrance toward complexation.     

Thermal decomposition and mass spectra of mixed ligand copper(II) complexes of 1,10-phenanthroline and coumarin derivatives

Four copper(II) new mix ligand complexes of the coumarin derivative (A¹ = 7-hydroxy-10,11-dihydroindeno[5,4-c]chromen-6(9H)-one, A² = 2-bromo-7-hydroxy-10,11- dihydroindeno[5,4-c]chromen-6(9H)-one, A³ = 7-hydroxy-4-methoxy-10,11-dihydroindeno[5,4-c]chromen-6(9H)-one, and A⁴ = 5-hydroxy-8,9-dihydrobenzo[f]indeno[5,4-c]chromen-4(7H)-one) and 1,10-Phenanthroline have been synthesized. The structural interpretations were confirmed from elemental analyses, magnetic susceptibility and FAB mass spectral, as well as from IR spectral studies. From the analytical, spectroscopic, and thermal data, the stoichiometry of the mentioned complexes was found to be 1:1:1 (coumarin ligand:copper metal:1,10-Phenanthroline). The thermal stabilities of these complexes were studied by thermogravimetric (TG/DTG) and the decomposition steps of these four complexes are investigated. Kinetic parameters such as order of reaction (n) and the energy of activation (E _a) were calculated using Freeman–Carroll method. The pre-exponential factor (A), the activation entropy (S*), the activation enthalpy (H*), and the free energy of activation (G*) were calculated using Horowitz–Matzger equations. Based on the E _a values, the thermal stabilities of complexes in the decreasing order are Cu(II)-2 > Cu(II)-3 > Cu(II)-4 > Cu(II)-1.     

Nucleophilic ligand substitution in triply deprotonated tetrapeptide complexes of copper(II) and nickel(II) with 1,10-phenanthroline and 2,2-bipyridine

Ligand substitution of the triply deprotonated tetrapeptide ligand with bulky α-carbon substituents, in the tetrapeptide complexes of Cu(II) and Ni(II) by the bidentate ligands 2,2-bipyridine and 1,10-phenanthroline has been studied. The mechanism in the Cu^II(H_-3A₄)^2? and the Cu^II(H_-3F₄)^2? complexes shows a proton-assisted nucleophilic attack, and the Cu^II(H_-3V₄)^2? shows both proton-assisted and direct equatorial nucleophilic attack by the bidentate ligands. A factor of ten decrease in the rate of substitution from Cu^II(H_-3A₄)^2? to Cu^II(H_-3V₄)^2?, and also Cu^II(H_-3F₄)^2? is an indication of a steric hindrance on the substitution rate because of atom overcrowding due to the size of the α-carbon substituents in the Cu^II(H_-3V₄)^2? and Cu^II(H_-3F₄)^2? complexes. The substitution of the triply deprotonated tetrapeptide ligand in Ni^II(H_-3A₄)^2? by 2,2-bipyridine and 1,10-phenanthroline shows a kinetic behaviour completely different to that of the Cu(II)-tetrapeptide complexes. Only a direct equatorial nucleophilic attack by the bidentate ligands has been observed.