Isomeric Ru Research Articles

Synthesis and reactivity of isomeric Ru complexes with hydroxypyridyl fragment: Active catalysts for β‑alkylation of secondary alcohols with primary alcohols

When the ligand LOH, containing a 2-hydroxy pyridine group, reacts with an equimolar amount of the precursor Ru(DMSO)4Cl2, two isomeric ruthenium complexes are formed. These isomers are termed cis-1 and trans-1, based on the relative positions of the N atom in N-(2-(6-hydroxy pyridin-2-yl)phenyl)acetamide and the pyridine groups of bis((1,4-pyridin-2-yl)methyl)amine. Treatment of these isomers with equimolar amounts of NaH results in deprotonation of the uncoordinated hydroxy pyridine groups, leading to the formation of complex 2 with newly coordinated pyridine groups. The catalytic activity of these three ruthenium complexes in the β-alkylation reaction of primary alcohols and secondary alcohols was evaluated, with complex 2 displaying the highest activity and selectivity. Complex 2 may be seen as an intermediate in the catalysis of the β-alkylation reaction by the isomers (cis-1 and trans-1). These findings are valuable for the development of more effective bifunctional catalysts.

Synthesis, Characterization, and Water Oxidation Activity of Isomeric Ru Complexes.

The synthesis and characterization of the isomeric ruthenium complexes with the general formula cis- and trans-[Ru(trpy)(qc)X]n+ (trpy is 2,2':6',2″-terpyridine, qc is 8-quinolinecarboxylate, cis-1 and trans-1, X = Cl, n = 0; cis-2 and trans-2, X=OH2, n = 1) with respect to the relative disposition of the carboxylate and X ligands are reported. For comparison purposes, another set of ruthenium complexes with general formula cis- and trans-[Ru(trpy)(pic)(OH2)]+ (pic is 2-picolinate (cis-3, trans-3)) have been prepared. The complexes with a qc ligand show a more distorted geometry compared to the complexes with a pic ligand. In all of the cases, the trans isomers show lower potential values for all of the redox couples relative to the cis isomers. Complexes cis-2 and trans-2 with six-member chelate rings show higher catalytic activity than cis-3 and trans-3. Overall, it was shown that the electronic perturbation to the metal center exerted by different orientation and geometry of the ligands significantly influences both redox properties and catalytic performance.

Single Site Isomeric Ru WOCs with an Electron-Withdrawing Group: Synthesis, Electrochemical Characterization, and Reactivity.

The synthetic intermediate cis(out),cis-[Ru(Cl)2(HL)(DMSO)2], 1 (DMSO = dimethyl sulfoxide), and four new mononuclear ruthenium complexes with general formula out/in-[Ru(HL)(trpy)(X)](m+) (trpy = 4-tert-butylpyridine; X = Cl(-), m = 1, 2a(+) and 2b(+); X = H2O, m = 2, 3a(2+) and 3b(2+)) based on the ligand 1H-pyrazole-3-carboxylic acid, 5-(2-pyridinil)-, ethyl ester (HL), are synthesized and characterized by analytical, spectroscopic, and electrochemical methods. A linkage isomerism is observed for a DMSO moiety of 1, and relevant thermodynamics and kinetics values are obtained through electrochemical experiments and compared to literature. Different synthetic routes are developed to obtain isomeric 2a(+) and 2b(+), with different relative yields. Water oxidation activity of 3a(2+) and 3b(2+) is analyzed by means of electrochemical methods, through foot of the wave analysis, yielding kobs values of 1.00 and 2.23 s(-1), respectively. Chemically driven water oxidation activity is tested using [(NH4)2Ce(NO3)6] as sacrificial electron acceptor, and turnover number (TON) and turnover frequency (TOF) values of TON = 10.8 and TOFi = 58.2 × 10(-3) s(-1) for 3a(2+) and TON = 4.2 and TOFi = 15.4 × 10(-3) s(-1) for 3b(2+) are obtained.

Dye sensitized solar cells with cobalt and iodine-based electrolyte: the role of thiocyanate-free ruthenium sensitizers

Isomeric Ru(ii) sensitizers, with varied steric impediment on TiO2, show high efficiency using Co2+/3+ electrolyte, with higher efficiency for the more symmetric isomers.

Photoinduced intramolecular energy transfer and anion sensing studies of isomeric RuIIOsIIcomplexes derived from an asymmetric phenanthroline–terpyridine bridge

Two heterobimetallic Ru(II)-Os(II) complexes of compositions [(bpy)2M(II)(phen-Hbzim-tpy)M'(II)(tpy-PhCH3)](4+), where M(II) = Ru and M'(II) = Os (4) and M(II) = Os and M'(II) = Ru (5), phen-Hbzim-tpy = 2-(4-(2,6-di(pyridin-2-yl)pyridine-4-yl)phenyl)-1H-imidazole[4,5][1,10]phenanthroline, bpy = 2,2'-bipyridine, and tpy-PhCH3 = 4'-(4-methylphenyl)-2,2':6',2''-terpyridine have been synthesized and characterized by elemental analyses, ESI mass spectrometry, and (1)H NMR and UV-vis absorption spectroscopy. The absorption spectra, redox behavior, and luminescence properties of the complexes have been thoroughly investigated and compared with that of monometallic model compounds [(bpy)2M(II)(phen-Hbzim-tpy)](2+) [M(II) = Ru (1) and M(II) = Os (2)] and [(phen-Hbzim-tpy)Ru(II)(tpy-PhCH3)](2+) (3). The complexes display very intense, ligand-centered absorption bands in the UV and moderately intense MLCT bands in the visible regions. The bimetallic complexes show two successive one-electron reversible metal-centered oxidations, whereas the monometallic complexes display one-electron oxidation in the positive potential window. Steady state and time-resolved luminescence data at room temperature show that an efficient intramolecular electronic energy transfer takes place from the Ru-center to the Os-based component in both the heterometallic dyads in all the solvents. The complexes under investigation contain an imidazole NH proton which became appreciably acidic due to metal coordination and can be utilized for recognition of selective anions in solution either via hydrogen bonding interaction or by proton transfer. Accordingly, the anion binding properties of the two heterobimetallic complexes as well as parent bridging ligand, phen-Hbzim-tpy, have been studied in solutions using absorption, steady state and time-resolved luminescence spectral measurements. The metalloreceptors act as sensors for F(-), CN(-) and AcO(-) ions. It is evident from sensing studies that in the presence of excess of selective anions, deprotonation of the imidazole N-H proton occurs in all cases.

Synthesis and properties of benzo[b]‐1,10‐phenanthrolines and their ruthenium(II) complexes

AbstractFriedländer reactions of 4‐aminoacridine‐3‐carbaldehyde with 1,3‐, 1,4‐di‐, and 1,3,5‐triacetylbenzenes afforded a series of corresponding (benzo[b]‐1,10‐phenanthrolin‐2‐yl)benzenes as new N,N,C‐polydentates. Reaction with 1,2‐diacetylbenzene afforded 1,2‐di(benzo[b]‐1,10‐phenanthrol‐2‐yl)benzene with unexpected benzo[b]‐1,10‐phenanthroline and 3‐oxoindeno[1,2‐b]benzo[j]‐1,10‐phenanthroline in a ratio of 1:1.2:1. Metal complex formation of the ligands was examined to provide two isomeric Ru complexes, a pentaaza‐coordinated (N5Cl) complex [Ru(tpy)(3aH)Cl](PF6) and a hexacoordinated (N5C) complex [Ru(tpy)(3a)](PF6) in a ratio of 1:4 with 71% overall yield, whereas 3b‐eH afforded complex mixtures upon reactions with Ru(tpy)Cl3. © 2007 Wiley Periodicals, Inc. Heteroatom Chem 18:650–656, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20358

Site-specific electronic couplings in dyads with MLCT excited states. Intramolecular energy transfer in isomeric Ru(ii)-Ru(ii) cyclometalated complexes

The rod-like binuclear complexes [(ttpy)Ru(tpy-ph(2)-phbpy)Ru(ttpy)](4+) and [(ttpy)Ru(tpy-ph(2)-tpy)Ru(phtbpy)](4+) (for abbreviations, see text) have been synthesized and characterized. In both complexes, the polypyridine Ru(II) centers have (N--N--N)Ru(N--N--N) and (N--N--N)Ru(C--N--N) coordination environment. The two isomeric species differ in whether the cyclometalating carbon resides on the bridging or on the terminal ligand. The two complexes have virtually identical energy levels, but MLCT excited states of different (bridging or terminal) ligand localization. They are thus ideally suited to investigate possible effects of excited-state localization on intramolecular energy transfer kinetics. In fact, ultrafast spectroscopic measurements yield different energy transfer time constants for the two isomers, with the bridge-cyclometalated complex (2.7 ps) being faster than the terminal-cyclometalated one (8.0 ps). This difference can be explained in terms of different electronic factors for Dexter energy transfer. The study highlights the peculiar intricacies of intramolecular energy transfer in inorganic dyads involving MLCT excited states.

Synthesis, structure, and spectroscopic, photochemical, redox, and catalytic properties of ruthenium(II) isomeric complexes containing dimethyl sulfoxide, chloro, and the dinucleating bis(2-pyridyl)pyrazole ligands.

Two isomeric Ru(II) complexes containing the dinucleating Hbpp (3,5-bis(2-pyridyl)pyrazole) ligand together with Cl and dmso ligands have been prepared and their structural, spectroscopic, electrochemical, photochemical, and catalytic properties studied. The crystal structures of trans,cis-[Ru(II)Cl(2)(Hbpp)(dmso)(2)], 2a, and cis(out),cis-[Ru(II)Cl(2)(Hbpp)(dmso)(2)], 2b, have been solved by means of single-crystal X-ray diffraction analysis showing a distorted octahedral geometry for the metal center where the dmso ligands coordinate through their S atom. 1D and 2D NMR spectroscopy corroborates a similar structure in solution for both isomers. Exposure of either 2a or 2b in acetonitrile solution under UV light produces a substitution of one dmso ligand by a solvent molecule generating the same product namely, cis(out)-[Ru(II)Cl(2)(Hbpp)(MeCN)(dmso)], 4. While the 1 e(-) oxidation of 2b or cis(out),cis-[Ru(II)Cl(2)(bpp)(dmso)(2)](+), 3b, generates a stable product, the same process for 2a or trans,cis-[Ru(II)Cl(2)(bpp)(dmso)(2)](+), 3a, produces the interesting linkage isomerization phenomenon where the dmso ligand switches its bond from Ru-S to Ru-O (K(III)(O)(-->)(S) = 0.25 +/- 0.025, k(III)(O)(-->)(S) = 0.017 s(-1), and k(III)(S)(-->)(O) = 0.065 s(-1); K(II)(O)(-->)(S) = 6.45 x 10(9), k(II)(O)(-->)(S) = 0.132 s(-1), k(II)(S)(-->)(O) = 2.1 x 10(-11) s(-1)). Finally complex 3a presents a relatively high activity as hydrogen transfer catalyst, with regard to its ability to transform acetophenone into 2-phenylethyl alcohol using 2-propanol as the source of hydrogen atoms.

Effect of steric hindrance on photoinduced electron transfer of self-assembled monolayers of three isomeric Ru(II)-bipyridine complexes on ITO electrode

Three kinds of self-assembled monolayers (SAMs) of isomeric Ru(II)-bipyridine complexes: cis-di(thiocyanato)-bis(2,2′-bipyridyl-3,3′-dicarboxylate) ruthenium (dye A), cis-di(thiocyanato)-bis(2,2′-bipyridyl-4,4′- dicarboxylate) ruthenium (dye B) and cis-di(thiocyanato)-bis(2,2′-bipyridyl-5,5′- dicarboxylate) ruthenium (dye C), were fabricated on hydrophilic transparent indium tin oxide (ITO) electrode. The UV-visible spectra, contact angle, XPS and cyclic voltammetry of these SAMs were measured. The photoinduced electron transfer properties were determined both in propylenecarbonate (PC) electrolyte and KCl electrolyte. A possible mechanism of electron transfer of these systems was proposed.

Efficient Stereospecific Syntheses of Chiral Ruthenium Dimers

The stereospecific synthesis of three isomeric Ru dimers, Δ,Δ-[(phen)2Ru(tpphz)Ru(phen)2]4+ (Δ,Δ-4) (where tpphz = tetrapyrido[3,2-a:2‘,3‘-c:3‘‘,2‘‘-h:2‘‘,3‘‘-j]phenazine), Λ,Λ-4, and Λ,Δ-4, can be accomplished in high yield with retention of optical activity by the formation of a phenazine ring between appropriately functionalized chiral precursors.

Syntheses, molecular structures and electrochemical behavior of two isomeric Ru(PhNpy) 2(PPh 3) 2 complexes

The title compounds, isomers of Ru(PhNpy) 2(PPh 3) 2 (PhNpy = the anion of 2-(N-anilino)-pyridine), having C 1 and C 2 symmetry, were prepared by reacting RuCl 2(PPh 3) 3 with LiPhNpy in toluene. The crystal and molecular structures of these compounds have been determined from three-dimensional X-ray study. Both compounds crystallize in the monoclinic space group P2 1/c with the following unit cell dimensions: C 1-isomer: a = 13.852(3), b = 18.872(3), c = 18.206(3), β = 84.32(5), V = 4736(2) and Z = 4. C 2-isomer: a = 11.166(9), b = 20.404(8), c = 20.716(16), β = 97.14(7), V = 4683(10) and Z = 4. The structures were refined to R = 0.053 (R w = 0.083) for the C 1-isomer and R = 0.055 (R w = 0.063) for the C 2-isomer. In the C 1-isomer, the coordinating atoms N-py, N-Ph and PPH 3 are all in cis-arrangement. In the C 2-isomer, the py-rings are trans to each other. The complexes are six-coordinate with four-membered chelate rings. The NRuN angle in the chelate rings is ca. 62° in each case. The RuP bond lengths lie in the range 2.286(3)–2.337(1) Å. The average RuN(py), and RuN(Ph) bond lengths are 2.083 Å and 2.171 Å, respectively. Dichloromethane solutions of the C 1 and C 2 isomers display two quasireversible oxidation waves at 0.480, 1.175 V and 0.290, 1.040 V, respectively. The responses have one-electron stoichiometry and are assignable to Ru III/Ru II and Ru IV/Ru III couples.