Trinuclear Ruthenium Complexes Research Articles

Syntheses, crystal structures and MMCT properties of diruthenium-based cyanido-bridged RuV/VI2-NC-RuII complexes.

The goal of this study was to investigate how the electron-donating capability around the lower valent metal ion and the electron-accepting capability of the higher valent metal ion influence metal to metal charge transfer (MMCT) properties in mixed-valence complexes. A series of trinuclear ruthenium complexes represented as [Ru2(ap-4-Me)3(CH3COO)NCRuCpMex(dppe)][PF6] (CpMex = polymethylcyclopentadienyl, x = 0, 1, and 5; and dppe = 1, 2-bis(diphenylphosphino)ethane, ap-4-Me = 2-anilino-4-methylpyridine) and their one-electron oxidized products were synthesized and fully characterized. The UV-vis-NIR spectra confirmed that as the electron donor character of the CpMex(dppe)RuCN fragment enhanced or the electron-accepting capability of the higher valent diruthenium cluster increased, the RuII → RuV2 or RuVI2 Ru2 MMCT bands shifted to lower energies, which was supported by TDDFT calculations.

A series of acac-ruthenium complexes with chiral Schiff base ligands: Synthesis, characterization and catalytic property

Four acac ruthenium precursors Ru(acac)2(n-PrCN)2 (acac = acetylacetonate) (1), Ru(acac)2(PhCN)2 (2), [Ru(hfac)(CH3CN)4](CF3SO3) (hfac = 1,1,1,5,5,5-hexafluoroacetylacetonate, 3), and Ru(acac)(dmso)3Cl (dmso = dimethyl sulfoxide) (4) were synthesized. Reactions of ruthenium precursor Ru(acac)2(n-PrCN)2 and chiral Schiff bases HLn afforded a series of Ru(acac)2Ln adducts (n = 1‒9) and a trinuclear ruthenium Schiff base complex (S)-(HNEt3)[(η3-O,N,O-L3)2Ru{μ-(η1-O-L3)4RuCl}Ru(η3-O,N,O-L3)2] (5). All complexes were characterized by NMR, FT-IR, HR-MS, and UV–vis spectroscopies along with electrochemistry properties. The structures of chiral Schiff base ligands (R)-HL8 and (S)-HL9, and ruthenium complexes 1–5 were unambiguously established by single-crystal X-ray diffraction. The good catalytic property of nine Ru(acac)2Ln complexes and the trinuclear ruthenium complex 5 with chiral Schiff base ligands for cyclopropanation of styrene was also presented.

Synthesis and characterization of multinuclear ruthenium clusters assembled by terminal alkyne alcohols and ortho-carborane diselenolate ligands

Two novel half-sandwich trinuclear ruthenium complexes bridged by ortho-carborane-1,2-diselenolato ligands (p-cymene)Ru3(Se2C2B10H10)2(Se2C2B10H9)[HCCH(cyclo-C6H10)OCCH(cyclo-C6H10)] (2) and (p-cymene)Ru3(Se2C2B10H10)2(Se2C2B10H9)[HCCH(CH3)2COCCHC(CH3)2] (3) have been prepared by the reactions of ortho-carborane-1,2-diselenolate ligands and [(p-cymene)RuCl2]2 with CHC(cyclo-C6H10)(OH) and CHCC(OH)(CH3)2, respectively. The complexes have been fully characterized by 1H, 13C, and 11B NMR, mass and IR spectroscopy as well as by element analyzes. The molecular structures of two complexes have been determined by single-crystal X-ray diffraction analyzes.

Structural, spectral, and photoreactivity properties of mono and polymetallated-2,2′-bipyridine ruthenium(II) complexes

Polymetallated-2,2′-bipyridine–ruthenium(II) complexes exhibit photosensitization properties and can enhance optically induced NO release, thus modeling multi-site catalysts. Two novel ruthenium-nitrosyl complexes [RuCl2LA(NO)]PF6 (herein called RuLANO, LA = 2,6-bis[(aniline)methyl]-pyridine) and [RuCl2(NO)({Ru(bpy)2}2-μ-LB)](PF6)5 (herein called Ru3LBNO, LB = 2,6-bis[(1,10-phenantroline-5-amine)methyl]-pyridine) were prepared and structurally characterized (1H-, 13C-, DEPT-135 NMR, FTIR, UV–Vis, elemental analysis, ESI-HRMS, and single crystal x-ray diffraction). RuLANO showed a trans configuration of the chloride ligands, and photo-release of chloride is the major process upon irradiation of RuLANO at 377 nm, along with some NO dissociation to a small extent. In contrast, the trinuclear ruthenium complex Ru3LBNO was found to be photo-inactive with irradiation between 377 and 447 nm (region of absorption of the {Ru(bpy)2(phen)}2+ chromophore) in the same conditions of RuLANO. This result agrees with the strong stabilization of Rucentral dxy, dxz, and dyz orbitals as shown by calculations using density functional theory (DFT), as well as with the electrochemical response, which supports that there is no major electronic communication between the central and the peripherals ruthenium ions in the trinuclear complex.

Anticancer and antitrypanosomal activities of trinuclear ruthenium compounds with orthometalated phenazine ligands.

Trinuclear ruthenium complexes with orthometalated phenazines of general formula [Ru3(μ3-O)(μ2-OAc)5(L)(py)2]PF6 (L = dppn, benzo[i]dipyrido[3,2-a:2',3'-c]phenazine, 1; dppz, dipyrido[3,2-a:2',3'-c]phenazine, 2; CH3-dppz, 7-methyldipyrido[3,2-a:2',3'-c]phenazine, 3; Cl-dppz, 7-chlorodipyrido[3,2-a:2',3'-c]phenazine, 4) were investigated for their cytotoxic activity toward the B16F10 murine melanoma and the L929 non-cancer cell lines and against Trypanosoma cruzi (2-4). This study also reports a multi-technique investigation into how complexes 1-4 interact with DNA and human serum albumin, HSA. At concentrations ranging from 2 to 50 μM, all the complexes reduced B16F10 murine melanoma cell viability by over 50%. Complex 4 had the highest cytotoxic effect in the series, diminishing B16F10 cell viability to 38% at 2 μM, with an overall order for anticancer activity of 4 > 2 > 3 > 1. Complexes 2-4 showed remarkable activity in inhibiting epimastigote and amastigote forms of T. cruzi. Complex 2 showed better antitrypanosomal activity than the reference drug (IC50 = 1.19 μM and IC50 = 0.25 μM for epimastigote and amastigotes forms, respectivily). Ethidium bromide (EB) displacement assays showed that DNA intercalation progressively increases with the extension of the π-conjugation of the cyclometalating ligand and the presence of substituents in the phenazinic portion (1 > 4-3 > 2), showing that complex 1 is a stronger intercalator than EB itself (Kapp > 107 M-1). Viscosity measurements followed the same trend. Cytotoxicity against cancer cells and antitrypanosomal activity follow the same order, which is different to the tendency of DNA intercalation, suggesting DNA is not the main target of these complexes. Compound 1-4 showed very high affinity with HSA (Kb ∼109 M-1). Circular dichroism results also showed that the complexes alter significantly the secondary structure of the HSA, lowering the α-helix % from 86.2 (pure protein) to less than 5% for compounds 1, 2 and 4 at 2.8 μM. These findings demonstrated the important role of phenazines for the biological activity of triruthenium compounds.

Synthesis and Structures of Ruthenium Carbonyl Complexes Bearing Pyridine-Alkoxide Ligands and Their Catalytic Activity in Alcohol Oxidation.

Reaction of Ru3(CO)12 with two equiv of 6-bromopyridine alcohols 6-bromopyCHROH [(R = C6H5 (L1); R = 4-CH3C6H4 (L2); R = 4-OMeC6H4 (L3); R = 4-ClC6H4 (L4); (R = 4-CF3C6H4 (L5); R = 2-OMeC6H4 (L6); R = 2-CF3C6H4 (L7)] and 6-bromopyC(Me)2OH (L8) in refluxing xylene afforded novel trinuclear ruthenium complexes [6-bromopyCHRO]2Ru3(CO)8 (1a-1g) and [6-bromopyC(Me)2O]2Ru3(CO)8 (1h). These complexes were characterized by FT-IR and NMR spectroscopy as well as elemental analysis. The structures of all the complexes were further confirmed by X-ray crystallographic analysis. In the presence of tert-butyl hydroperoxide (TBHP) as the source of oxidant, complexes 1a-1h displayed high catalytic activities for oxidation of primary and secondary alcohols and most of oxidation reactions could be completed within 1 h at room temperature.

Photoinduced Oxidation of Water with Potassium Persulfate in the Presence of Ruthenium Trinuclear Complex

The kinetics and mechanism of the photoinduced reaction of water oxidation with potassium persulfate in the presence of the tris(bipyridyl) complex bpy3RuCl2 ∙ 6H2O as a photosensitizer and the trinuclear ruthenium complex (NH3)5Ru–O–Ru(NH3)4–O–Ru(NH3)5Cl6 have been studied. It has been shown that this complex is converted to a more active water oxidation catalyst when four or five NH3 ligands are replaced by oxygen atoms.

Oxidation of Water by Cerium(IV) Compounds in the Presence of Trinuclear Ruthenium Complexes

The oxidation of water by Ce(IV) compounds in the presence of ruthenium complex (NH3)5Ru–O–Ru(NH3)4–O–Ru(NH3)5Cl6 is studied. It is shown that the complex is a catalyst of water oxidation if one-electron oxidizing species Ce4+ are used. Four units of the indicated ruthenium complex then organize themselves into a reactive dodecanuclear cluster. It is established that the formation of bi-, tetra-, and polynuclear cerium clusters in the reacting system is accompanied by the four oxygen atoms in the catalyst molecule being replaced with 4NH3 ligands, resulting in a different catalytic system for biomimetic water oxidation.

New uses for old complexes: The very first report on the trypanocidal activity of symmetric trinuclear ruthenium complexes

This work reports on the trypanocidal activity of a series of symmetric triruthenium complexes combined with azanaphthalene ligands of general formula [Ru3O(CH3COO)6(L)3]PF6 (L=(1) quinazoline (qui), (2) 5-nitroisoquinoline (5-nitroiq), (3) 5-bromoisoquinoline (5-briq), (4) isoquinoline (iq), (5) 5-aminoisoquinoline (5-amiq), and (6) 5,6,7,8-tetrahydroisoquinoline (thiq)). All complexes within the series presented in vitro trypanocidal activity against both the trypomastigote and amastigote forms of T. cruzi. The IC50 values obtained for complexes 1–6 ranged from 1.39 to 165.9μM for the trypomastigote form and from 1.06 to 53.16μM for the amastigote form. These values were lower than the values observed for the metallic core [Ru3O(CH3COO)6(CH3OH)3]+ itself and for the free ligands in all cases. Remarkably, complex 6 displayed lower IC50 values than the reference drug (benznidazole) for the acute (trypomastigote form) and chronic (amastigote form) phases of Chagas disease. These findings, combined with the low toxicity against healthy cells (LLK-MK2 strain) and a high SI value (Selectivity Index >10) make complex 6 an excellent candidate for in vivo tests.

Polyelectrochromism and electronic coupling in vinylruthenium-modified carbazoles

Six carbazole-derived mono-, di- and trinuclear ruthenium complexes featuring one to three square pyramidal, five-coordinated {Ru(CO)Cl(PiPr3)2(CHCH-)} entities were prepared by the regio- and stereospecific insertion of the hydride precursor HRu(CO)Cl(PiPr3)2 into the CC bond of the corresponding ethynylated N-substituted carbazoles. They were characterized by IR, UV/Vis, and NMR spectroscopy, electrochemistry, and, in up to four different oxidation states, by UV/Vis/NIR and IR spectroelectrochemistry. Their radical cations were additionally investigated by EPR spectroscopy. Experimental studies are complemented by (TD-)DFT calculations. Electrochemical studies on these complexes showed two to four reversible, consecutive one-electron oxidation processes. Half-wave potential separations ΔE½ between individual redox-waves and the derived comproportionation constants Kc indicate that intermediate oxidation states are sufficiently stable with respect to disproportionation to be generated and investigated in solution. Spectroscopic data indicate strong carbazole ligand contributions to every oxidation and notable involvement of the vinylruthenium moieties to the lower oxidation steps. UV/Vis/NIR spectroelectrochemistry reveals a polyelectrochomic behavior of all complexes with, however, less pronounced absorptivities when compared to the simple triarylamine counterparts. The pattern of two separate, moderately spaced Ru(CO) bands for the MV radical cations IIa+, IIb+ and III+ indicates that the unipositive charge is unevenly distributed over the two chemically equivalent vinylruthenium subunits.

Synthesis of Diruthenium Complexes Derived from Pyridyl-Substituted Indenes

Thermal treatment of the trinuclear ruthenium complex {μ2-η5:η1-(C5H4N)(C9H5)}Ru3(CO)9 (1) with 1,5-heptadiene, diallyl sulfide, 1,4-hexadiene, and 1,7-octadiene respectively generated the series of diruthenium products {(C5H4N)(μ2-η5,η1-C9H5CHCH2CH2R)}Ru2(CO)x (4, R = −CH2CH═CHCH3; 6, R = SCH2CH═CH2; 7, R = −CH═CHCH3; 8, R = −(CH2)3CH═CH2) via the insertion of an terminal C═C bond into the Ru–C(η1) bond of 1. When 1 was treated with diallyl ether, the complex {(C5H4N)(μ2-η5,η3-C9H5CCH2CH2OCCHCH3)}Ru2(CO)4 (5) with a five-membered oxygen-containing heterocycle was produced. Reactions of 2-methyl-3-(2-pyridyl)indene or 2,5-dimethyl-3-(2-pyridyl)indene with Ru3(CO)12 gave the cycloruthenated complexes {(C5H4N)(μ2-η5,η1-RC9H4CH2)}Ru2(CO)5 (9, R = H; 10, R = CH3) with structures similar to those of 4, 7, and 8, via C(sp3)–H activation. The molecular structures of 5–7 and 10 were determined by X-ray diffraction.

Long-Range Intramolecular Electronic Communication in a Trinuclear Ruthenium Tropolonate Complex

Dinuclear and trinuclear ruthenium complexes, [Ru(trop)2(C2trop)Ru(dppe)Cp] [2b; trop = tropolonato, C2trop = ethynyltropolonato, dppe = 1,2-bis(diphenylphosphino)ethane] and [Ru(trop){(C2trop)Ru(dppe)Cp}2] (3), were synthesized, and their electronic and electrochemical properties were investigated in comparison with our previously reported complex [Ru(acac)2(C2trop)Ru(dppe)Cp] (2a). The electron-donating RuII(dppe)Cp unit and electron-accepting RuIIIO6 unit are connected by C2trop in these complexes. 2a incorporates acetylacetonate as an ancillary ligand, while 2b and 3 incorporate tropolonate as an ancillary ligand. Every complex, 2a, 2b, and 3, exhibits similar UV-vis-near-IR (NIR) absorption spectra, demonstrating the lack of explicit intramolecular electronic communication between the units at least in the neutral state. The weak NIR absorption in 2a further diminished upon electrochemical oxidation, indicating almost no electronic communication between the units. In contrast, 2b and 3 exhibit broad NIR absorptions upon oxidation. Additionally, 3 exhibits four stepwise redox couples in the electrochemical study, which are formally attributed to [RuII(trop)3]-/[RuIII(trop)3], two [RuII(dppe)Cp]/[RuIII(dppe)Cp]+, and [RuIII(trop)3]/[RuIV(trop)3]+ couples. Clear separation of the redox couples attributed to the two terminal [Ru(dppe)Cp] units demonstrates the thermodynamic stability of the intermediate oxidation states with respect to disproportionation. Further electrochemical studies using an electrolyte including perfluorinated weakly coordinating anions and density functional theory/time-dependent density functional theory calculations confirmed the effect of ancillary ligands, acetylacetonate and tropolonate. In the case of 2a, electronic delocalization over the whole complex, especially over the [Ru(acac)2(trop)] unit, appears to be small. In contrast, the electronic communication between [Ru(dppe)Cp] and [Ru(trop)3] units in 3 seems to be enhanced upon oxidation, resulting in the long-range intramolecular electronic communication.

An extended π-system and enhanced electronic delocalization on symmetric [Ru3O(CH3COO)6(L)3]n complexes combined with azanaphthalene ligands.

We report on the investigation of a new series of symmetric trinuclear ruthenium complexes combined with azanaphthalene ligands: [Ru3O(CH3COO)6(L)3]PF6 where L = (1) quinazoline (qui), (2) 5-nitroisoquinoline (5-nitroiq), (3) 5-bromoisoquinoline (5-briq), (4) isoquinoline (iq), (5) 5-aminoisoquinoline (5-amiq), and (6) 5,6,7,8-tetrahydroisoquinoline (thiq). The crystal structure of complex 1, [Ru3O(CH3COO)6(qui)3]PF6, was determined by X-ray diffraction analysis, showing a high degree of co-planarity between the [Ru3O] plane and the azanaphthalene ligands. Spectroscopic (UV-visible, NMR and infra-red) and electrochemical (cyclic voltammetry and spectroelectrochemistry) data showed correlation with the pKa values of the azanaphthalene ligands and this dependence was rationalized in terms of the molecular orbital of the [Ru3O] unit and the structure of the ligands. By analysing the spectroscopic and electrochemical correlations, the ability of the azanaphthalene ligands to extend the electronic π-system of the [Ru3O] unit to the periphery of the compounds was demonstrated. This electronic effect accounts for the planarity of the structure of complex 1. It was also shown through molecular modeling results that, to explain the spectroscopic and electrochemical behaviour of these species, it is not possible to neglect the electronic mixing between the metallic and the acetate orbitals. Finally, this work revealed that electronic coupling is more pronounced in the azanaphthalene series of complexes than in pyridinic analogues and it is this coupling that determines the spectroscopic and electrochemical behaviour of the new species.

Redox‐Active‐Ligand‐Mediated Formation of an Acyclic Trinuclear Ruthenium Complex with Bridging Nitrido Ligands

AbstractCoordination of a redox‐active pyridine aminophenol ligand to RuII followed by aerobic oxidation generates two diamagnetic RuIII species [1 a (cis) and 1 b (trans)] with ligand‐centered radicals. The reaction of 1 a/1 b with excess NaN3 under inert atmosphere resulted in the formation of a rare bis(nitrido)‐bridged trinuclear ruthenium complex with two nonlinear asymmetrical Ru‐N‐Ru fragments. The spontaneous reduction of the ligand centered radical in the parent 1 a/1 b supports the oxidation of a nitride (N3−) to half an equivalent of N2. The trinuclear omplex is reactive toward TEMPO‐H, tin hydrides, thiols, and dihydrogen.

Redox-Active-Ligand-Mediated Formation of an Acyclic Trinuclear Ruthenium Complex with Bridging Nitrido Ligands.

Coordination of a redox-active pyridine aminophenol ligand to Ru(II) followed by aerobic oxidation generates two diamagnetic Ru(III) species [1 a (cis) and 1 b (trans)] with ligand-centered radicals. The reaction of 1 a/1 b with excess NaN3 under inert atmosphere resulted in the formation of a rare bis(nitrido)-bridged trinuclear ruthenium complex with two nonlinear asymmetrical Ru-N-Ru fragments. The spontaneous reduction of the ligand centered radical in the parent 1 a/1 b supports the oxidation of a nitride (N(3-) ) to half an equivalent of N2 . The trinuclear omplex is reactive toward TEMPO-H, tin hydrides, thiols, and dihydrogen.

A trinuclear ruthenium complex as a highly efficient molecular catalyst for water oxidation.

A trinuclear ruthenium complex, 3, was designed and synthesized with the ligand 2,2'-bipyridine-6,6'-dicarboxylic acid (bda) and we found that this complex could function as a highly efficient molecular catalyst for water oxidation in homogeneous systems. This trinuclear molecular water oxidation catalyst, 3, displayed much higher efficiencies in terms of turnover numbers and initial oxygen evolution rate than its counterparts, a binuclear catalyst, 2, and a mononuclear catalyst, 1, in both chemically driven and photochemically driven water oxidation based on either the whole catalytic molecules or just the active Ru centers. The reasons for the superior performance of catalyst 3 were discussed and we believe that multiple Ru centers in a single molecule are indeed beneficial for increasing the probability of the formation of O-O bonds through an intramolecular radical coupling pathway.

Studying the interaction between trinuclear ruthenium complexes and human serum albumin by means of fluorescence quenching

This work reports for the first time a systematic investigation of the interaction between HSA and trinuclear ruthenium complexes, by using fluorescence spectroscopy and the Stern–Volmer model. The compounds investigated have general formula [Ru3O(CH3COO)6(3-pic)2(L)]PF6, where L=NO or H2O and 3-pic=3-methylpyridine. For both complexes it was observed that the increase of Ksv values (in the order of 104M−1) with increasing temperature, signaling a dynamic quenching of HSA fluorescence. However, analysis of the quenching rate constants and Kb values shows that the contribution of the static quenching is significant. Particularly in the case of the nitrosyl complex, the relatively high value of Kb observed (178.44×103M−1, 308K) suggests that this compound can be efficiently stored and transported in the body by HSA. The interaction of the complexes with HSA is spontaneous (ΔG<0). Complex [Ru3O(CH3COO)6(3-pic)2(NO)]PF6 displays interaction with HSA by hydrophobic forces (∆H=215kJmol−1 and ∆S=796Jmol−1K−1), likely because of the nitrosyl lipophilicity, while complex [Ru3O(CH3COO)6(3-pic)2(H2O)]PF6 is involved in the formation of hydrogen bonds with HSA (∆H=−75.5kJmol−1 and ∆S=−231Jmol−1K−1), through its aquo ligand.

New trinuclear dendritic complexes with [Ru(tpy)(bpy)X]n + (X = Cl, H2O; n = 1, 2) for enhanced water oxidation and light-driven alcohol oxidation

A symmetric trinuclear ruthenium complex with [Ru(tpy)(bpy)(Cl)]+ (tpy=2,2′:6′,2″-terpyridine; bpy=2,2′-bipyridine) connected by 2,4,5-trimethylbenzene was easily prepared. The complex showed effective chemical water oxidation and light-driven oxidation activity of alcohols to corresponding aldehydes in water. When Cl− is replaced by H2O, the resulting complex exhibited over a twofold increase in O2 evolution activity compared with its parent complex. Moreover, compared with equimolar ruthenium amounts of the mononuclear complex with the H2O ligand, the trinuclear ruthenium complex with the conjugated ligand motif also displayed a two time increase in water oxidation activity.

Investigation of a novel trinuclear μ-oxo ruthenium complex as a potential nitric oxide releaser for biological purposes

The chemical properties of the trinuclear ruthenium complex [Ru3O(CH3COO)6(3-pic)2(NO)]PF6 (1, were 3-pic=3-picoline or 3-methylpyridine), its photochemical behavior and its ability as a vasorelaxing agent are reported in this work. It was shown that the unpaired electrons of NO and of the metal center [Ru3O]+ are tightly coupled, promoting an intermediate NMR profile between the oxidized (paramagnetic) and reduced (diamagnetic) [Ru3O]1+/0 species. From IR measurements, it was suggested that in trinuclear complexes, unlike other ruthenium compounds, the interaction of those unpaired electrons overcomes the effect of peripheral ligands and NO-backbonding on the ν(NO) frequency, which shows no dependence on the pKa values of pyridinic ligands. The photoinduced NO release was investigated by light irradiation at 337, 447, 532 and 660nm in phosphate buffer solution (pH 7.4), leading to the generation of gaseous NO0 and the solvated species [Ru3O(CH3COO)6(3-pic)2(H2O)]+ (2). Through amperometric and quimioluminescence measurements, the amount of NO(g) released were determined, showing dependence on the wavelength of irradiation. The ability of compound 1 as a vasorelaxing agent was also addressed. It was shown that, under ambient luminosity, compound 1 promotes 89% of relaxation in pre-contracted rat aorta. Molecular modeling of the novel nitrosyl, as well as characterization of the complexes [Ru3O(CH3COO)6(3-pic)2(L)]n, L=H2O, n=+1 (2), L=3-pic, n=+1 (3), L=CO, n=0 (4), are also reported.

Reactivity of a trinuclear ruthenium complex involving C–H activation and insertion of alkene

Synthesis, structure and reactivity of a pyridyl-substituted indenyl trinuclear ruthenium complex were researched.