Spontaneous CO Release from RuII(CO)2–Protein Complexes in Aqueous Solution,Cells, and Mice

We demonstrate that Ru^II(CO)₂–protein complexes, formed by the reaction of the hydrolytic decomposition products of [fac‐RuCl(κ²‐H₂NCH₂CO₂)(CO)₃] (CORM‐3) with histidine residues exposed on the surface of proteins, spontaneously release CO in aqueous solution, cells, and mice. CO release was detected by mass spectrometry (MS) and confocal microscopy using a CO‐responsive turn‐on fluorescent probe. These findings support our hypothesis that plasma proteins act as CO carriers after in vivo administration of CORM‐3. CO released from a synthetic bovine serum albumin (BSA)–Ru^II(CO)₂ complex leads to downregulation of the cytokines interleukin (IL)‐6, IL‐10, and tumor necrosis factor (TNF)‐α in cancer cells. Finally, administration of BSA–Ru^II(CO)₂ in mice bearing a colon carcinoma tumor results in enhanced CO accumulation at the tumor. Our data suggest the use of Ru^II(CO)₂–protein complexes as viable alternatives for the safe and spatially controlled delivery of therapeutic CO in vivo.     

Mapping the Transformation [{RuII(CO)3Cl2}2]→[RuI2(CO)4]2+: Implications in Binuclear Water–Gas Shift Chemistry

The complete sequence of reactions in the base‐promoted reduction of [{Ru^II(CO)₃Cl₂}₂] to [Ru^I₂(CO)₄]²⁺ has been unraveled. Several μ‐OH, μ:κ²‐CO₂H‐bridged diruthenium(II) complexes have been synthesized; they are the direct results of the nucleophilic activation of metal‐coordinated carbonyls by hydroxides. The isolated compounds are [Ru₂(CO)₄(μ:κ²‐C,O‐CO₂H)₂(μ‐OH)(NP^F‐Am)₂][PF₆] ( 1 ; NP^F‐Am=2‐amino‐5,7‐trifluoromethyl‐1,8‐naphthyridine) and [Ru₂(CO)₄(μ:κ²‐C,O‐CO₂H)(μ‐OH)(NP‐Me₂)₂][BF₄]₂ ( 2 ), secured by the applications of naphthyridine derivatives. In the absence of any capping ligand, a tetranuclear complex [Ru₄(CO)₈(H₂O)₂(μ³‐OH)₂(μ:κ²‐C,O‐CO₂H)₄][CF₃SO₃]₂ ( 3 ) is isolated. The bridging hydroxido ligand in 1 is readily replaced by a π‐donor chlorido ligand, which results in [Ru₂(CO)₄(μ:κ²‐C,O‐CO₂H)₂(μ‐Cl)(NP‐PhOMe)₂][BF₄] ( 4 ). The production of [Ru₂(CO)₄]²⁺ has been attributed to the thermally induced decarboxylation of a bis(hydroxycarbonyl)–diruthenium(II) complex to a dihydrido–diruthenium(II) species, followed by dinuclear reductive elimination of molecular hydrogen with the concomitant formation of the Ru^I? Ru^I single bond. This work was originally instituted to find a reliable synthetic protocol for the [Ru₂(CO)₄(CH₃CN)₆]²⁺ precursor. It is herein prescribed that at least four equivalents of base, complete removal of chlorido ligands by Tl^I salts, and heating at reflux in acetonitrile for a period of four hours are the conditions for the optimal conversion. Premature quenching of the reaction resulted in the isolation of a trinuclear Ru^I₂Ru^II complex [{Ru(NP‐Am)₂(CO)}{Ru₂(NP‐Am)₂(CO)₂(μ‐CO)₂}(μ₃:κ³‐C,O,O′‐CO₂)][BF₄]₂ ( 6 ). These unprecedented diruthenium compounds are the dinuclear congeners of the water–gas shift (WGS) intermediates. The possibility of a dinuclear pathway eliminates the inherent contradiction of pH demands in the WGS catalytic cycle in an alkaline medium. A cooperative binuclear elimination could be a viable route for hydrogen production in WGS chemistry.     

Judicious Ligand Design in Ruthenium Polypyridyl CO2 Reduction Catalysts to Enhance Reactivity by Steric and Electronic Effects

A series of Ru^II polypyridyl complexes of the structural design [Ru^II(R?tpy)(NN)(CH₃CN)]²⁺ (R?tpy=2,2′:6′,2′′‐terpyridine (R=H) or 4,4′,4′′‐tri‐tert‐butyl‐2,2′:6′,2′′‐terpyridine (R=tBu); NN=2,2′‐bipyridine with methyl substituents in various positions) have been synthesized and analyzed for their ability to function as electrocatalysts for the reduction of CO₂ to CO. Detailed electrochemical analyses establish how substitutions at different ring positions of the bipyridine and terpyridine ligands can have profound electronic and, even more importantly, steric effects that determine the complexes’ reactivities. Whereas electron‐donating groups para to the heteroatoms exhibit the expected electronic effect, with an increase in turnover frequencies at increased overpotential, the introduction of a methyl group at the ortho position of NN imposes drastic steric effects. Two complexes, [Ru^II(tpy)(6‐mbpy)(CH₃CN)]²⁺ (trans‐[ 3 ]²⁺; 6‐mbpy=6‐methyl‐2,2′‐bipyridine) and [Ru^II(tBu?tpy)(6‐mbpy)(CH₃CN)]²⁺ (trans‐[ 4 ]²⁺), in which the methyl group of the 6‐mbpy ligand is trans to the CH₃CN ligand, show electrocatalytic CO₂ reduction at a previously unreactive oxidation state of the complex. This low overpotential pathway follows an ECE mechanism (electron transfer–chemical reaction–electron transfer), and is a direct result of steric interactions that facilitate CH₃CN ligand dissociation, CO₂ coordination, and ultimately catalytic turnover at the first reduction potential of the complexes. All experimental observations are rigorously corroborated by DFT calculations.     

Electrochemical behaviour of [Ru(L)(CO)2Cl2] [Ru(L)(CO)Cl3][Me4N] and [Ru(L)(CO)2(CH3CN)2][CF3SO3]2 complexes (L = 2,2′- bipyridine or 4,4′-isopropoxycarbonyl-2,2′-bipyridine)

The clectrochemical behaviour of the complexes [Ru^II(L)(CO)₂Cl₂], [Ru^II(L)(CO)Cl₃][Me₄N] and [Ru^II(L)(CO)₂(CH₃CN)₂][CF₃SO₃]₂ (L = 2,2′-bipyridine or 4,4′-isopropoxycarbonyl-2,2′-bipyridine) has been investigated in CH₃CN. The oxidation of [Ru(L)(CO)₂Cl₂] produces new complexes [Ru^III(L)(CO)(CH₃CN)₂Cl]²⁺ as a consequence of the instability of the electrogenerated transient Ru^III species [Ru^III(L)(CO)₂Cl₂]⁺. In contrast, the oxidation of [Ru^II(L)(CO)Cl₃][Me₄N] produces the stable [Ru^III(L)(CO)Cl₃] complex. In contrast [Ru^II(L)(CO)₂(CH₃CN)₂][CF₃SO₃]₂ is not oxidized in the range up to the most positive potentials achievable. The reduction of [Ru^II(L)(CO)₂Cl₂] and [Ru^II(L)(CO)₂(CH₃CN)₂][CF₃SO₃]₂ results in the formation of identical dark blue strongly adherent electroactive films. These films exhibit the characteristics of a metal-metal bond dimer structure. No films are obtained on reduction of [Ru^II(L)(CO)Cl₃][Me₄N]. The effect of the substitution of the bipyridine ligand by electron-withdrawing carboxy ester groups on the electrochemical behaviour of all these complexes has also been investigated.     

An N‐Acetyl Cysteine Ruthenium Tricarbonyl Conjugate Enables Simultaneous Release of CO and Ablation of Reactive Oxygen Species

We have designed and synthesised a [Ru(CO)₃Cl₂(NAC)] pro‐drug that features an N‐acetyl cysteine (NAC) ligand. This NAC carbon monoxide releasing molecule (CORM) conjugate is able to simultaneously release biologically active CO and to ablate the concurrent formation of reactive oxygen species (ROS). Complexes of the general formulae [Ru(CO)₃(L)₃]²⁺, including [Ru(CO)₃Cl(glycinate)] (CORM‐3), have been shown to produce ROS through a water–gas shift reaction, which contributes significantly, for example, to their antibacterial activity. In contrast, NAC‐CORM conjugates do not produce ROS or possess antibacterial activity. In addition, we demonstrate the synergistic effect of CO and NAC both for the inhibition of nitric oxide (formation) and in the expression of tumour‐necrosis factor (TNF)‐α. This work highlights the advantages of combining a CO‐releasing scaffold with the anti‐oxidant and anti‐inflammatory drug NAC in a unique pro‐drug.     

A SIMPLE ROUTE FOR SYNTHESES OF TRIHALIDE-BRIDGED CARBONYL DIRUTHENIUM(II,III) COMPLEXES: CRYSTAL AND MOLECULAR STRUCTURE OF ttt-[RuIICl2(CO)2(PPh3)2],[(CO)(AsPh3)2RuII(μ-Cl3)RuIIICl2(AsPh3)] AND ([CO)(PPh3)2RuII(μ-Br3)RuIIIBr2(PPh3)], SPECTROSCOPIES,ELECTROCHEMISTRY AND PROPERTIES

Abstract

The triply halide-bridged binuclear complexes [Ru₂Cl₅(CO)(AsPh₃)₃] (AsPh₃ = triphenylarsine), [Ru₂Cl₅(CO)(PPh₃)₂(AsPh₃)] (PPh₃ = triphenylphosphine), [Ru₂Cl₅(CO)(AsPh₃)₂(PPh₃)], [Ru₂ Br₅(CO)(PPh₃)₃], [Ru₂Cl₅(CO)(P{p-tol}₃)₂(PPh₃)] (P{p-tol}₃ = tri-p-tolylphosphine) and [Ru₂ Br₂Cl₃(PPh₃)₂(AsPh₃)] were prepared from the precursor compounds ttt-[RuX₂(CO)₂(P)₂] (X = Cl or Br) and [RuY₃(P')₂S]·S (Y = Cl or Br; P=PPh₃, AsPh₃ or P{p- tol}₃ and P' = AsPh₃ or PPh₃; S=DMA or MeOH, where DMA = N,N'-dimethylacetamide). The molecular structures of the binuclear complexes [Ru₂Cl₅(CO)(AsPh₃)₃] (P2_1/c), [Ru₂Br₅(CO)(PPh₃)₃] (P2_1/c) and ttt-[RuCl₂(CO)₂(PPh₃)₂] (P1) were determined by X-ray diffraction methods. The complexes are always formed by two Ru atoms bridged through three halide anions, two of which are × type (from the Ru^II precursor) and the other is Y type (from the ruthenium^III precursor) confirming our previously suggested mechanism for obtaining this class of complexes. The Ru^II atom is also coordinated to a carbon monoxide molecule and two P ligands from the ttt-starting isomer whereas the Ru^III atom is bonded to two non-bridging Y halides and one P' molecule. The presence of Ru^III was confirmed by EPR data, a technique that was also useful to suggest the symmetry of the complexes. The absence of intervalence charge-transfer transitions (IT) in the near infrared spectrum confirms that the binuclear complexes have localized valence. The IR spectra of the complexes show; (CO) bands close to 1970 cm^?1 and ν(Ru-Cl) or(Ru-Br) bands at about 230–380 cm^?1 corresponding to halides at terminal or bridged positions. Two widely separated redox processes, Ru^II/Ru^II←Ru^II/Ru^III→Ru^III/Ru^III, were observed by cyclic voltammetry and differential pulse voltammetry.     

Synthesis and Characterization of New Water‐Soluble Hydrides of RuII: A Step towards Dinitrogen Activation?

The basic aqueous coordination chemistry of Ru^II has been studied using the catalytically important TPPTS phosphine (TPPTS=trisodium salt of 3,3′,3″‐phosphinetriylbenzenesulfonic acid) and small gas molecules (H₂, CO, N₂) as ligands. As a result, new water‐soluble ruthenium mixed hydride complexes, presumably key species in many industrial catalytic processes, have been formed and identified. The Ru^II mixed hydrides were synthesized, and their formation was followed in situ by multinuclear NMR spectroscopy, pressurizing aqueous Ru^II? TPPTS systems with H₂ and CO gas in sapphire NMR tubes. The formation equilibrium of these complexes is highly dependant on the temperature and the gas pressures. Under 50 atm of N₂, the unique [RuH(CO)(N₂)(TPPTS)₂(H₂O)]⁺ complex has been identified, which could be the first step toward dinitrogen activation.     

Theoretical Insights into the Mechanism of Carbon Monoxide (CO) Release from CO‐Releasing Molecules

We used density functional theory to investigate the capacity for carbon monoxide (CO) release of five newly synthesized manganese‐containing CO‐releasing molecules (CO‐RMs), namely CORM‐368 ( 1 ), CORM‐401 ( 2 ), CORM‐371 ( 3 ), CORM‐409 ( 4 ), and CORM‐313 ( 5 ). The results correctly discriminated good CO releasers ( 1 and 2 ) from a compound unable to release CO ( 5 ). The predicted Mn? CO bond dissociation energies were well correlated (R²≈0.9) with myoglobin (Mb) assay experiments, which quantified the formation of MbCO, and thus the amount of CO released by the CO‐RMs. The nature of the Mn? CO bond was characterized by natural bond orbital (NBO) analysis. This allowed us to identify the key donor–acceptor interactions in the CO‐RMs, and to evaluate the Mn? CO bond stabilization energies. According to the NBO calculations, the charge transfer is the major source of Mn? CO bond stabilization for this series. On the basis of the nature of the experimental buffers, we then analyzed the nucleophilic attack of putative ligands (L′=HPO₄^2?, H₂PO₄^?, H₂O, and Cl^?) at the metal vacant site through the ligand‐exchange reaction energies. The analysis revealed that different L′‐exchange reactions were spontaneous in all the CO‐RMs. Finally, the calculated second dissociation energies could explain the stoichiometry obtained with the Mb assay experiments.     

Ruthenium(II/III)‐Based Compounds with Encouraging Antiproliferative Activity against Non‐small‐Cell Lung Cancer

Hereby we present the synthesis of several ruthenium(II) and ruthenium(III) dithiocarbamato complexes. Proceeding from the Na[trans‐Ru^III(dmso)₂Cl₄] ( 2 ) and cis‐[Ru^II(dmso)₄Cl₂] ( 3 ) precursors, the diamagnetic, mixed‐ligand [Ru^IIL₂(dmso)₂] complexes 4 and 5 , the paramagnetic, neutral [Ru^IIIL₃] monomers 6 and 7 , the antiferromagnetically coupled ionic α‐[Ru^III₂L₅]Cl complexes 8 and 9 as well as the β‐[Ru^III₂L₅]Cl dinuclear species 10 and 11 (L=dimethyl‐ (DMDT) and pyrrolidinedithiocarbamate (PDT)) were obtained. All the compounds were fully characterised by elemental analysis as well as ¹H NMR and FTIR spectroscopy. Moreover, for the first time the crystal structures of the dinuclear β‐[Ru^III₂(dmdt)₅]BF₄ ? CHCl₃ ? CH₃CN and of the novel [Ru^IIL₂(dmso)₂] complexes were also determined and discussed. For both the mono‐ and dinuclear Ru^II and Ru^III complexes the central metal atoms assume a distorted octahedral geometry. Furthermore, in vitro cytotoxicity of the complexes has been evaluated on non‐small‐cell lung cancer (NSCLC) NCI‐H1975 cells. All the mono‐ and dinuclear Ru^III dithiocarbamato compounds (i.e., complexes 6 – 10 ) show interesting cytotoxic activity, up to one order of magnitude higher with respect to cisplatin. Otherwise, no significant antiproliferative effect for either the precursors 2 and 3 or the Ru^II complexes 4 and 5 has been observed.     

Comparative Study of Ruthenium(II) and Ruthenium(III) Complexes with the Ligand dmbpy (dmbpy = 4, 4′‐Dimethyl‐2, 2′‐bipyridine)

The complex cis‐[Ru^III(dmbpy)₂Cl₂](PF₆) ( 2 ) (dmbpy = 4, 4′‐dimethyl‐2, 2′‐bipyridine) was obtained from the reaction of cis‐[Ru^II(dmbpy)₂Cl₂] ( 1 ) with ammonium cerium(IV) nitrate followed by precipitation with saturated ammonium hexafluoridophosphate. The ¹H NMR spectrum of the Ru^III complex confirms the presence of paramagnetic metal atoms, whereas that of the Ru^II complex displays diamagnetism. The ³¹P NMR spectrum of the Ru^III complex shows one signal for the phosphorus atom of the PF₆^– ion. The perspective view of each [Ru^II/III(dmbpy)₂Cl₂]^0/+ unit manifests that the ruthenium atom is in hexacoordinate arrangement with two dmbpy ligands and two chlorido ligands in cis position. As the oxidation state of the central ruthenium metal atom becomes higher, the average Ru–Cl bond length decreases whereas the Ru–N (dmbpy) bond length increases. The cis‐positioned dichloro angle in Ru^III is 1.3° wider than that in the Ru^II. The dihedral angles between pair of planar six‐membered pyridyl ring in the dmbpy ligand for the Ru^II are 4.7(5)° and 5.7(4)°. The observed inter‐planar angle between two dmbpy ligands in the Ru^II is 89.08(15)°, whereas the value for the Ru^III is 85.46(20)°.     

Coordination Booster‐Catalyst Assembly: Remote Osmium Outperforming Ruthenium in Boosting Catalytic Activity

Presented herein is a set of bimetallic and trimetallic “coordination booster‐catalyst” assemblies in which the coordination complexes [Ru^II(terpy)₂] and [Os^II(terpy)₂] acted as boosters for enhancement of the catalytic activity of [Ru^II(NHC)(para‐cymene)]‐based catalytic site. The boosters accelerated the oxidative loss of para‐cymene from the catalytic site to generate the active catalyst during the oxidation of alkenes and alkynes into corresponding aldehydes, ketones and diketones. It was found that the boosting efficiency of the [Os^II(terpy)₂] units was considerably higher than its congener [Ru^II(terpy)₂] unit in these assemblies. Mechanistic studies were conducted to understand this unique improvement.     

Alcohol oxidation reactions catalyzed by ruthenium–carbonyl complexes of thioarylazoimidazoles

Alcohols are oxidized by N‐methylmorpholine‐N‐oxide (NMO), Bu^tOOH and H₂O₂ to the corresponding aldehydes or ketones in the presence of catalyst, [RuH(CO)(PPh₃)₂(SRaaiNR′)]PF₆ ( 2 ) and [RuCl(CO)(PPh₃)(S_κRaaiNR′)]PF₆ ( 3 ) (SRaaiNR′ ( 1 ) = 1‐alkyl‐2‐{(o‐thioalkyl)phenylazo}imidazole, a bidentate N(imidazolyl) (N), N(azo) (N′) chelator and S_κRaaiNR′ is a tridentate N(imidazolyl) (N), N(azo) (N′), S_κ‐R is tridentate chelator; R and R′ are Me and Et). The single‐crystal X‐ray structures of [RuH(CO)(PPh₃)₂(SMeaaiNMe)]PF₆ ( 2a ) (SMeaaiNMe = 1‐methyl‐2‐{(o‐thioethyl)phenylazo}imidazole) and [RuH(CO)(PPh₃)₂(SEtaaiNEt)]PF₆ ( 2b ) (SEtaaiNEt = 1‐ethyl‐2‐{(o‐thioethyl)phenylazo}imidazole) show bidentate N,N′ chelation, while in [RuCl(CO)(PPh₃)(S_κEtaaiNEt)]PF₆ ( 3b ) the ligand S_κEtaaiNEt serves as tridentate N,N′,S chelator. The cyclic voltammogram shows Ru^III/Ru^II (~1.1 V) and Ru^IV/Ru^III (~1.7 V) couples of the complexes 2 while Ru^III/Ru^II (1.26 V) couple is observed only in 3 along with azo reductions in the potential window +2.0 to ?2.0 V. DFT computation has been used to explain the spectra and redox properties of the complexes. In the oxidation reaction NMO acts as best oxidant and [RuCl(CO)(PPh₃)(S_κRaaiNR′)](PF₆) ( 3 ) is the best catalyst. The formation of high‐valent Ru^IV=O species as a catalytic intermediate is proposed for the oxidation process. Copyright © 2014 John Wiley & Sons, Ltd.     

Photochemical Reduction of Low Concentrations of CO2 in a Porous Coordination Polymer with a Ruthenium(II)–CO Complex

Direct use of low pressures of CO₂ as a C1 source without concentration from gas mixtures is of great interest from an energy‐saving viewpoint. Porous heterogeneous catalysts containing both adsorption and catalytically active sites are promising candidates for such applications. Here, we report a porous coordination polymer (PCP)‐based catalyst, PCP‐Ru^II composite, bearing a Ru^II‐CO complex active for CO₂ reduction. The PCP‐Ru^II composite showed improved CO₂ adsorption behavior at ambient temperature. In the photochemical reduction of CO₂ the PCP‐Ru^II composite produced CO, HCOOH, and H₂. Catalytic activity was comparable with the corresponding homogeneous Ru^II catalyst and ranks among the highest of known PCP‐based catalysts. Furthermore, catalytic activity was maintained even under a 5 % CO₂/Ar gas mixture, revealing a synergistic effect between the adsorption and catalytically active sites within the PCP‐Ru^II composite.     

DNA-Targeting RuII-Polypyridyl Complex with a Long-Lived Intraligand Excited State as a Potential Photodynamic Therapy Agent

Subtle ligand modifications on Ru^II-polypyridyl complexes may result in different excited-state characteristics, which provides the opportunity to tune their photo-physicochemical properties and subsequently change their biological functions. Here, a DNA-targeting Ru^II-polypyridyl complex (named Ru1 ) with highly photosensitizing ³IL (intraligand) excited state was designed based on a classical DNA-intercalator [Ru(bpy)₂(dppz)] ⋅ 2 PF₆ by incorporation of the dppz (dipyrido[3,2-a:2′,3′-c]phenazine) ligand tethered with a pyrenyl group, which has four orders of magnitude higher potency than the model complex [Ru(bpy)₂(dppz)] ⋅ 2 PF₆ upon light irradiation. This study provides a facile strategy for the design of organelle-targeting Ru^II-polypyridyl complexes with dramatically improved photobiological activity.     

Ketimido Metallophthalocyanines: An Approach to Phthalocyanine‐Supported Mononuclear High‐Valent Ruthenium Complexes

A “metal–ketimine+ArI(OR)₂” approach has been developed for preparing metal–ketimido complexes, and ketimido ligands are found to stabilize high‐valent metallophthalocyanine (M? Pc) complexes such as ruthenium(IV) phthalocyanines. Treatment of bis(ketimine) ruthenium(II) phthalocyanines [Ru^II(Pc)(HN?CPh₂)₂] ( 1a ) and [Ru^II(Pc)(HNQu)₂] ( 1b ; HNQu=N‐phenyl‐1,4‐benzoquinonediimine) with PhI(OAc)₂ affords bis(ketimido) ruthenium(IV) phthalocyanines [Ru^IV(Pc)(N?CPh₂)₂] ( 2a ) and [Ru^IV(Pc)(NQu)₂] ( 2b ), respectively. X‐ray crystal structures of 1b and [Ru^II(Pc)(PhN?CHPh)₂] ( 1c ) show Ru? N(ketimine) distances of 2.075(4) and 2.115(3) Å, respectively. Complexes 2a , 2b readily revert to 1a , 1b upon treatment with phenols. ¹H NMR spectroscopy reveals that 2a , 2b are diamagnetic and 2b exists as two isomers, consistent with a proposed eclipsed orientation of the ketimido ligands in these ruthenium(IV) complexes. The reaction of 1a , 1b with PhI(OAc)₂ to afford 2a , 2b suggests the utility of ArI(OR)₂ as an oxidative deprotonation agent for the generation of high‐valent metal complexes featuring M? N bonds with multiple bonding characters. DFT and time‐dependent (TD)‐DFT calculations have been performed on the electronic structures and the UV/Vis absorption spectra of 1b and 2b , which provide support for the diamagnetic nature of 2b and reveal a significant barrier for rotation of the ketimido group about the Ru? N(ketimido) bond.     

NLO active CuII/RuII and CdII/RuII coordination-organometallic complexes: synthesis,structural characterization and photoluminescence properties

Cu^II/Ru^II and Cd^II/Ru^II hybrid complexes [Cu(L_1–3)(NC₅H₄C≡CRu(dppe)₂Cl)] (1a-3a) and [Cd(L_1-3)(NC₅H₄C≡CRu(dppe)₂Cl)] (1b–3b) have been prepared by reaction of trans-[RuCl(dppe)₂(C≡C-py-3)] (1) with copper or cadmium acetate in the presence of Schiff base ligands L_H1–3 (where L_H = 2-(pyrrole-2-yl-methylidine)aminophenol (L_H1), 5-bromo-2-(pyrrole-2-yl-methylidine)aminophenol (L_H2) and 5-nitro-2-(pyrrole-2-yl-methylidine)aminophenol (L_H3)). The hybrid materials were characterized on the basis of elemental analyses, TEM, IR, UV–visible, ¹H NMR, and ³¹P NMR spectral studies. TEM overview observations revealed well-dispersed spherical nanoparticles of ~60 nm are formed. Quasireversible redox behavior is observed for Cu^II/Ru^II complexes corresponding to Cu^I/Cu^II and Ru^II/Ru^III couples. All the complexes exhibit blue-green emission as a result of fluorescence from the intraligand (π → π*) emission excited state with good quantum yield. The second-order nonlinear optical (NLO) properties of Cu^II/Ru^II and Cd^II/Ru^II complexes have been investigated by the Kurtz-powder method. The second harmonic generation efficiency of these complexes show that these complexes are NLO active and display good second-order nonlinear optical activity.     

Redox‐Controlled Exchange Bias in a Supramolecular Chain of Fe4 Single‐Molecule Magnets

Tetrairon(III) single‐molecule magnets [Fe₄(pPy)₂(dpm)₆] ( 1 ) (H₃pPy=2‐(hydroxymethyl)‐2‐(pyridin‐4‐yl)propane‐1,3‐diol, Hdpm=dipivaloylmethane) have been deliberately organized into supramolecular chains by reaction with Ru^IIRu^II or Ru^IIRu^III paddlewheel complexes. The products [Fe₄(pPy)₂(dpm)₆][Ru₂(OAc)₄](BF₄)_x with x=0 ( 2 a ) or x=1 ( 2 b ) differ in the electron count on the paramagnetic diruthenium bridges and display hysteresis loops of substantially different shape. Owing to their large easy‐plane anisotropy, the s=1 diruthenium(II,II) units in 2 a act as effective s_eff=0 spins and lead to negligible intrachain communication. By contrast, the mixed‐valent bridges (s=3/2, s_eff=1/2) in 2 b introduce a significant exchange bias, with concomitant enhancement of the remnant magnetization. Our results suggest the possibility to use electron transfer to tune intermolecular communication in redox‐responsive arrays of SMMs.     

Ruthenium(II)–Polyimine–Coumarin Light‐Harvesting Molecular Arrays: Design Rationale and Application for Triplet–Triplet‐Annihilation‐Based Upconversion

Ru^II–bis‐pyridine complexes typically absorb below 450 nm in the UV spectrum and their molar extinction coefficients are only moderate (ε<16 000 M ^?1 cm^?1). Thus, Ru^II–polyimine complexes that show intense visible‐light absorptions are of great interest. However, no effective light‐harvesting ruthenium(II)/organic chromophore arrays have been reported. Herein, we report the first visible‐light‐harvesting Ru^II–coumarin arrays, which absorb at 475 nm (ε up to 63 300 M ^?1 cm^?1, 4‐fold higher than typical Ru^II–polyimine complexes). The donor excited state in these arrays is efficiently converted into an acceptor excited state (i.e., efficient energy‐transfer) without losses in the phosphorescence quantum yield of the acceptor. Based on steady‐state and time‐resolved spectroscopy and DFT calculations, we proposed a general rule for the design of Ru^II–polypyridine–chromophore light‐harvesting arrays, which states that the ¹IL energy level of the ligand must be close to the respective energy level of the metal‐to‐ligand charge‐transfer (M LCT) states. Lower energy levels of ¹IL/³IL than the corresponding ¹M LCT/³M LCT states frustrate the cascade energy‐transfer process and, as a result, the harvested light energy cannot be efficiently transferred to the acceptor. We have also demonstrated that the light‐harvesting effect can be used to improve the upconversion quantum yield to 15.2 % (with 9,10‐diphenylanthracene as a triplet‐acceptor/annihilator), compared to the parent complex without the coumarin subunit, which showed an upconversion quantum yield of only 0.95 %.     

Synthesis,spectral characterization,electrochemical studies and catalytic properties in Suzuki–Miyaura coupling reactions of the mononuclear PdII,trinuclear PdII(BPh2)2 and RuII?PdII?RuII type complexes containing 4‐amino‐1‐benzyl piperidine and phenyl groups

The ligand containing the 4‐amino‐1‐benzyl piperidine group, N, N′‐(4‐amino‐1‐benzyl piperidine)‐glyoxime, (LH₂) (1) was prepared from 4‐amino‐1‐benzyl piperidine with anti‐dichloroglyoxime at ? 15 °C in absolute Tetrahydrofuran (THF). In the trinuclear [Pd(L)₂Ru₂(phen)₄](ClO₄)₂ (4) and [Pd(L)₂Ru₂(bpy)₄](ClO₄)₂ (5) metal complexes, the Pd^II ion centered into the main oxime core by the coordination of the imino groups while the two Ru^II ions coordinated dianionic oxygen donors of the oxime groups and linked to the ligands of 1,10‐phenanthroline and 2,2′‐bipyridine. The mono and trinuclear metal complexes were characterized by elemental analyses, FT‐IR, UV–vis, ¹H and ¹³C‐NMR spectra, magnetic susceptibility measurements, molar conductivity, cyclic voltammetry, mass spectra, X‐ray powder techniques and their morphology by SEM measurements. The cyclic voltammetric results show that the cathodic peak (E_pc) potential of (3) shifts towards more positive values compared with that of (2) as a result of the BPh₂⁺‐bridged complex formation. The Suzuki–Miyaura reaction was used to investigate their activity as catalyst either prepared in‐situ or from well‐defined complexes. Copyright © 2008 John Wiley & Sons, Ltd.     

Synthesis and structures of ruthenium di‐ and tricarbonyl complexes derived from 4,5‐diazafluoren‐9‐one

Carbon monoxide (CO) has recently been shown to impart beneficial effects in mammalian physiology and considerable research attention is now being directed toward metal–carbonyl complexes as a means of delivering CO to biological targets. Two ruthenium carbonyl complexes, namely trans‐dicarbonyldichlorido(4,5‐diazafluoren‐9‐one‐κ²N,N′)ruthenium(II), [RuCl₂(C₁₁H₆N₂O)(CO)₂], (1), and fac‐tricarbonyldichlorido(4,5‐diazafluoren‐9‐one‐κN)ruthenium(II), [RuCl₂(C₁₁H₆N₂O)(CO)₃], (2), have been isolated and structurally characterized. In the case of complex (1), the trans‐directing effect of the CO ligands allows bidentate coordination of the 4,5‐diazafluoren‐9‐one (dafo) ligand despite a larger bite distance between the N‐donor atoms. In complex (2), the cis disposition of two chloride ligands restricts the ability of the dafo molecule to bind ruthenium in a bidentate fashion. Both complexes exhibit well defined ¹H NMR spectra confirming the diamagnetic ground state of Ru^II and display a strong absorption band around 300 nm in the UV.