Ruthenium N-heterocyclic Carbene Complexes Research Articles

Hydrodefluorination of Fluoroaromatics by Isopropyl Alcohol Catalyzed by a Ruthenium NHC Complex. An Unusual Role of the Carbene Ligand

The NHC (NHC = N-heterocyclic carbene) complex Cp*(IPr)RuH3 catalyzes hydrodefluorination of aromatic fluorides at 70 °C with isopropyl alcohol as the reducing reagent. The reaction is selective for aromatic fluorides, as almost negligible C(sp3)–F bond reduction takes place. The activity decreases from more to less fluorinated substrates, but polyaromatic monofluorides, such as 1-fluoronaphthalene and 6-fluoro-2-methylquinoline, can also be reduced in moderate to good yields. Kinetic studies are consistent with a mechanism based on elimination of NHC and reversible substrate coordination, followed by coordination of the alcohol.

Ruthenium(II) DMSO complexes with CˆC* cyclometalated phenylimidazol NHC ligands

We present the synthesis of cyclometalated ruthenium N-heterocyclic carbene (NHC) complexes of the general formula [Ru(CˆC*)(DMSO)3Cl] and their use as starting material for the synthesis of a heteroleptic 2,2′-bipyridine (bpy) complex [Ru(bpy)(CˆC*)(DMSO)Cl]. Starting from the corresponding η6-(p-cymene) complexes [Ru(p-cymene)(CˆC*)Cl], the π-coordinated aryl ligand is substituted by three S-bound dimethyl sulfoxide ligands. In the course of this substitution, the complexes undergo a change in geometry from facial to meridional, which is unambiguously proven by solid state structure determination and DFT calculations. The labile DMSO ligands can be substituted by bidentate ligands as shown for the widely used 2,2′-bipyridine. The resulting air- and moisture-stable heteroleptic complex features two bidentate (CˆC* + bpy) and two monodentate (Cl− + DMSO) ligands.

Dehydrogenative Synthesis of Carboxylic Acids from Primary Alcohols and Hydroxide Catalyzed by a Ruthenium N-Heterocyclic Carbene Complex.

Primary alcohols have been reacted with hydroxide and the ruthenium complex [RuCl2(IiPr)(p-cymene)] to afford carboxylic acids and dihydrogen. The dehydrogenative reaction is performed in toluene, which allows for a simple isolation of the products by precipitation and extraction. The transformation can be applied to a range of benzylic and saturated aliphatic alcohols containing halide and (thio)ether substituents, while olefins and ester groups are not compatible with the reaction conditions. Benzylic alcohols undergo faster conversion than other substrates, and a competing Cannizzaro reaction is most likely involved in this case. The kinetic isotope effect was determined to be 0.67 using 1-butanol as the substrate. A plausible catalytic cycle was characterized by DFT/B3LYP-D3 and involved coordination of the alcohol to the metal, β-hydride elimination, hydroxide attack on the coordinated aldehyde, and a second β-hydride elimination to furnish the carboxylate.

Synthesis and catalytic activity of supported acenaphthoimidazolylidene N-heterocyclic carbene ruthenium complex for ring closing metathesis (RCM) and ring opening metathesis polymerization (ROMP)

Ruthenium catalyzed ring closing metathesis (RCM) and ring opening metathesis polymerization (ROMP) reactions using a supported bis(arylimino)acenaphthene N-heterocyclic carbene (BIAN-NHC) complex have been reported. The BIAN-NHC Ru-complex exhibits excellent catalytic activity and tolerates a wide range of substrates at low catalyst loadings. DFT calculations were also carried out on some selected key intermediates in the reaction mechanism to study the effect of having the conjugated aromatic moiety (BIAN-NHC) in the backbone of the complex. The newly synthesized BIAN-NHC Ru-complex shows comparable catalytic activities to the commercially available second generation Ru catalyst HG2. The recycled complex was reused for up to eight reaction cycles for the RCM of N,N-diallyl tosylamine affording a high average isolated yield, with lower levels of Ru contamination in the final product.▪

Isolation of [Ru(IPr)2(CO)H]+ (IPr = 1,3-Bis(2,6-diisopropylphenyl)imidazol-2-ylidene) and Reactivity toward E–H (E = H, B) Bonds

Halide abstraction from the ruthenium N-heterocyclic carbene complex Ru(IPr)2(CO)HCl (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) with NaBAr4F (BAr4F = B{C6H3(3,5-CF3)2}4) gave the salt [Ru(IPr)2(CO)H]BAr4F (2), which was shown through a combined X-ray/neutron structure refinement and quantum theory of atoms in molecules (QTAIM) study to contain a bifurcated Ru···η3-H2C ξ-agostic interaction involving one iPr substituent of the IPr ligand. This system complements the previously reported [Ru(IMes)2(CO)H]+ cation (IMes =1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene), where a non-agostic form is favored. Treatment of 2 with CO, H2, and the amine–boranes H3B·NR2H (R = Me, H) gave [Ru(IPr)2(CO)3H]BAr4F (3), [Ru(IPr)2(CO)(η2-H2)H]BAr4F (4), and [Ru(IPr)2(CO)(κ2-H2BH·NR2H)H]BAr4F (R = Me, 5; R = H, 6), respectively. Heating 5 in the presence of Me3SiCH═CH2 led to alkene hydroboration and formation of the C–H activated product [Ru(IPr)(IPr)′(CO)]BAr4F (7). X-ray characterization of 3 and 5–7 was co...

PH sensitive chitosan-mesoporous silica nanoparticles for targeted delivery of a ruthenium complex with enhanced anticancer effects.

Nanocarriers are widely used for delivering drugs to tumors and their development is progressing steadily. In this study, a pH sensitive mesoporous silica nanocarrier, RuNHC@MSNs-CTS-Biotin (CTS = chitosan), is developed for the targeted delivery and controlled release of a ruthenium(ii) N-heterocyclic carbene (RuNHC) complex. The RuNHC@MSNs-CTS-Biotin nanoparticles were composed of RuNHC loaded mesoporous silica nanoparticles (MSNs) coated with chitosan-biotin (CTS-Biotin) conjugates. CTS traps the RuNHC complex inside the mesopores and biotin is used as a targeting ligand to improve specific cell uptake. The particle size of RuNHC@MSNs-CTS-Biotin was around 90 nm with a zeta potential of 12.0 mV and the RuNHC loading capacity was 26.31%. The release of RuNHC from RuNHC@MSNs-CTS-Biotin was in a pH-dependent manner, and it exhibited a 59.71% terminal release ratio at pH 5.0, but almost no release under neutral conditions (pH 7.4). Its in vitro cellular uptake and anticancer activity revealed that RuNHC@MSNs-CTS-Biotin could be selectively internalized in cancer cells by biotin receptor-mediated endocytosis and this resulted in a significant improvement in anticancer activities as compared with the RuNHC complex. This multifunctional nanocarrier system provides a promising platform for the development of precisely controllable cancer therapy.

Synthesis of ruthenium N-heterocyclic carbene complexes and their catalytic activity for β-alkylation of tertiary cyclic amines

The novel ruthenium N-Heterocyclic carbene complexes are synthesized, and characterized by studying its 1H, 13C, elemental analysis, and X-ray. These complexes have been reported as promising catalyst for β C–H bond functionalization of tertiary cyclic amines through hydrogen autotransfers in the presence of external acidic additive. The new catalytic products were characterized by 1H NMR, 13C NMR spectroscopic methods.

Erratum to: N-Propylphthalimide-Substituted Silver(I) N-Heterocyclic Carbene Complexes and Ruthenium(II) N-Heterocyclic Carbene Complexes: Synthesis and Transfer Hydrogenation of Ketones

This study deals with the synthesis of N-propylphthalimide substituted Ag(I)–N-heterocyclic carbene (NHC) complexes and N-propylphthalimide substituted Ru(II)–NHC complexes in the transfer hydrogenation of ketones. The Ag(I)–NHC complexes were synthesized from the imidazolium salts and Ag2O in dichloromethane at room temperature. The Ru(II)–NHC complexes have been prepared from Ag(I)–NHC complexes using transmetallation method. The six N-propylphthalimide substituted Ag(I)–NHC complexes and six N-propylphthalimide substituted Ru(II)–NHC complexes have been characterized by spectroscopic techniques and elemental analyses. N-propylphthalimide substituted Ru(II)–NHC complexes have been analyzed as catalysts for the transfer hydrogenation of ketones and exhibit activity in this reaction. This study deals with the synthesis of N-propylphthalimide substituted Ag(I)-N-heterocyclic carbene (NHC) complexes and N-propylphthalimide substituted Ru(II)–NHC complexes in the transfer hydrogenation of ketones. The Ag(I)–NHC complexes were synthesized from the imidazolium salts and Ag2O in dichloromethane at room temperature. The Ru(II)–NHC complexes have been prepared from Ag(I)–NHC complexes using transmetallation method. The six N-propylphthalimide substituted Ag(I)–NHC complexes and six N-propylphthalimide substituted Ru(II)–NHC complexeshavebeencharacterizedbyspectroscopictechniquesandelementalanalyses. N-propylphthalimide substituted Ru(II)–NHC complexes have been analyzed as catalysts for the transfer hydrogenation of ketones and exhibit activity in this reaction.

Net charge effects in N-heterocyclic carbene–ruthenium complexes with similar oxidation states and coordination geometries

A chelating benzimidazolylidene–carboxylate ligand (1) was transferred from [Ag(1)] to [RuCl2(dmso)4] to afford trans(C)-[Ru(1)2(bpy)] (2), but all attempts to incorporate 1 into cis(Cl)-[RuCl2(bpy)2] were unsuccessful. Alternatively, reaction of [RuCl(1)(η6-cymene)] (3) with bpy and AgOTf successfully produced [Ru(1)(bpy)2][OTf] (4). Methylation of 2 and 4 with MeOTf yielded trans(C)-[Ru(1-Me)2(bpy)][OTf]2 (5) and [Ru(1-Me)(bpy)2][OTf]2 (6), accompanied by a +2 and +1 increase in net charge, respectively. Cyclic voltammetry indicated that the increase in Ru(II)/Ru(III) oxidation potential from 2 to 5 was twice the increase from 4 to 6. UV–Vis spectroscopy also revealed that transitions in 5 occurred at higher energy than in 2 by double the difference between 6 and 4. Crystallographic analysis demonstrated that the coordination environment of Ru did not differ significantly between 2 and 5, suggesting that the observed shifts in oxidation potentials and absorption wavelengths are not due to changes in coordination chemistry or formal oxidation state. Collectively, these results show that 5 and 6 feature Ru centers more electron deficient than those in 2 and 4, respectively, by amounts linearly proportional to the difference in net charge.

Lipophilicity-dependent ruthenium N-heterocyclic carbene complexes as potential anticancer agents.

Five Ru(II)-N-heterocyclic carbenes (NHC) (1-5) were synthesized by reacting the appropriately substituted imidazolium chlorides with Ag2O, forming the NHC-silver chloride in situ followed by transmetalation with dimeric p-cymene ruthenium(II) dichloride. All the complexes were characterized by NMR and ESI-MS, and complex 1 was also characterized by single-crystal X-ray diffraction. The IC50 values of these five complexes were determined by the MTT-based assay on four human cancer cell lines, SKOV-3 (ovarian), PC-3 (prostate), MDA-MB-231 (breast) and EC109 (esophagus). The cytotoxicities of these complexes changed from a moderate effect to a fine one, corresponding to the increasing lipophilicity order of the complex of 2 < 1 < 3 < 4 < 5 (0.91, 0.88, 1.36, 1.85 and 2.62 for 1–5 respectively). Complex 5 showed the most cytotoxicity with the IC50 values 10.3 ± 0.3 μM for SKOV-3, 2.9 ± 0.1 μM for PC-3, 8.2 ± 0.6 μM for MDA-MB-231, 6.4 ± 0.2 μM for EC109 cell lines. Due to the superior cytotoxicity of complex 5 against the PC-3 cell lines, further biological evaluations were carried out to elucidate its action mechanism. The morphologic changes and cell cycle analysis showed that complex 5 can inhibit PC-3 cell lines by inducing cell cycle arrest at the G2/M phase. The DNA binding experiments further demonstrate that complex 5 has a better binding ability for DNA (Kb = 2.2 × 10(6) M(-1)) than complexes 1-4 (3.8 × 10(5), 7.0 × 10(5), 5.7 × 10(5), and 1.9 × 10(5) respectively).

4-Vinylbenzyl-substituted silver(I) N-heterocyclic carbene complexes and ruthenium(II) N-heterocyclic carbene complexes: synthesis and transfer hydrogenation of ketones

4-Vinylbenzyl-substituted Ag(I) N-heterocyclic carbene (NHC) complexes and Ru(II) NHC complexes have been synthesized. The Ag(I) complexes were synthesized from the imidazolium salts and Ag2O in dichloromethane at room temperature. The Ru(II) complexes were prepared from Ag(I) NHC complexes by transmetallation. The six 4-Vinylbenzyl-substituted Ag(I) NHC complexes and six 4-Vinylbenzyl-substituted Ru(II) NHC complexes have been characterized by spectroscopic techniques and elemental analyses. The Ru(II) NHC complexes show catalytic activity for the transfer hydrogenation of ketones.

On the viability of ruthenium (II) N-heterocyclic carbene complexes as dye-sensitized solar cell (DSSCs): A theoretical study

Changes in the ground state and excited state properties of the [Ru(bpy)3]2+ complex induced by functionalization of bpy ligands with N-heterocyclic carbene ligand (imidazolylidene, benzimidazolylidene and 1,2,3-triazolylidene) and substituted methyl wingtip group in protonated and deprotonated forms were studied theoretically using DFT and TDDFT methods. The absorption band is broader and features approximately a 26nm more bathochromic tail than the [Ru(bpy)3]2+. Our calculations show that red shift for 1,2,3-triazolylidene ligand in the protonated series is only due to the affect of the energies of LUMOs which is localized on the substituted ligands. Consistent with previously observed trends in absorption spectra of Ru (II) complexes, a blue shift is observed for the deprotonated series. The effect originates from interplay of positive and negative solvatochromism in 1–3 and 1a–3a complexes respectively. This results in more delocalized character of the electron transition orbitals in the deprotonated complexes. We performed an NTO analysis based on the calculated transition density matrices to analyze the calculated singlet states. The calculated triplet excited state can either be weakly optically allowed 3MLCT or optically forbidden Ru 3d–d transitions. The ability to reduce the HOMO–LUMO gap by the carbene ligand is expected to be beneficial for photovoltaic applications.

Synthesis, characterization, and transfer hydrogenation of Ru(II)-N-heterocyclic carbene complexes

A new series of ruthenium(II) N-heterocyclic carbene complexes [RuL1,2,3(p-cymene)Cl2] (3a–c) (where L is a N-heterocyclic carbene), have been synthesized via transmetalation. The new ruthenium(II)-NHC complexes were applied to transfer hydrogenation of acetophenone derivatives and aldehydes using 2-propanol as a hydrogen source and KOH as a co-catalyst. The results show that the corresponding alcohols could be obtained in good yield with high catalyst activity (up to 100%) under mild conditions. [RuL1(p-cymene)Cl2] (3a) is much more active than the other complexes in transfer hydrogenation. Reactions, catalyzed by 3a–c, showed the highest reaction rates and yields of alcohol when the substrates bear more electron-withdrawing substituents. All new compounds were characterized by IR, elemental analysis, LC–MS (ESI), and NMR spectroscopy.

Donor functionalized ruthenium N-heterocyclic carbene complexes in alcohol oxidation reactions

N-Pyridyl, N'-amido functionalized imidazolium bromides were obtained in high yields as an N-heterocyclic carbene (NHC) precursor and used as bidentate or a pincer ligands to obtain ruthenium complexes via a silver NHC transmetallation route. The incorporation of a phenyl group as an amido-N substituent (R = Ph) results in a bidentate coordination mode through the C(NHC) and N(pyridyl) donors, whereas in its absence (R = H) a pincer coordination mode was observed through the N(pyridyl)^C(NHC)^O(amido) donors. The ruthenium complex featuring a pincer type NCO coordination mode with a protic NH function adjacent to the coordinating O(amido) atom was found to efficiently catalyse the oxidation of activated alcohols effecting quantitative conversions within 30 minutes. However the oxidation of deactivated alcohols required longer reaction times to effect the quantitative transformation.

Synthesis of N-Heterocyclic Carbene Ruthenium Complex and Application as Catalyst for Suzuki Coupling Reaction

Synthesis of N-Heterocyclic Carbene Ruthenium Complex and Application as Catalyst for Suzuki Coupling Reaction

Evaluation of arene ruthenium(ii) N-heterocyclic carbene complexes as organometallics interacting with thiol and selenol containing biomolecules

Metal complexes with N-heterocyclic carbene (NHC) ligands have been widely used in catalytic chemistry and are now increasingly considered for the development of new chemical tools and metal based drugs. Ruthenium complexes of the type (p-cymene)(NHC)RuCl(2) interacted with biologically relevant thiols and selenols, which resulted in the inhibition of enzymes such as thioredoxin reductase or cathepsin B. Pronounced antiproliferative effects could be obtained provided that an appropriate cellular uptake was achieved. Inhibition of tumor cell growth was accompanied by a perturbation of metabolic parameters such as cellular respiration.

Synthesis of ruthenium(II) N-heterocyclic carbene complexes and their catalytic activities in transfer hydrogenation of ketones

Three RuCl2(η6-arene, η1-carbene) and two RuCl2(NHC)(arene) complexes have been prepared by the reaction of bis(1,3-dialkylperhydrobenzimidazol-2-ylidene) (1) and bis(1,3-dialkyl-4-methylzimidazolin-2-ylidene) (3) with [RuCl2(arene)]2 in toluene and characterized by elemental analysis, 1H NMR, 13C NMR and IR spectroscopy. The catalytic activities of these complexes were examined in the transfer hydrogenation of aromatic ketones using 2-propanol as hydrogen source.

ChemInform Abstract: A Computational Perspective of Olefins Metathesis Catalyzed by N‐Heterocyclic Carbene Ruthenium (Pre)catalysts.

AbstractReview: 93 refs.

Dehydrogenative Synthesis of Imines from Alcohols and Amines Catalyzed by a Ruthenium N-Heterocyclic Carbene Complex

A new method for the direct synthesis of imines from alcohols and amines is described where hydrogen gas is liberated. The reaction is catalyzed by the ruthenium N-heterocyclic carbene complex [RuCl2(IiPr)(p-cymene)] in the presence of the ligand DABCO and molecular sieves. The imination can be applied to a variety of primary alcohols and amines and can be combined with a subsequent addition reaction. A deuterium labeling experiment indicates that the catalytically active species is a ruthenium dihydride. The reaction is believed to proceed by initial dehydrogenation of the alcohol to the aldehyde, which stays coordinated to ruthenium. Nucleophilic attack of the amine affords the hemiaminal, which is released from ruthenium and converted into the imine.

Polyethylene Oligomer Supported Olefin Metathesis Catalysts

Polyethylene (PE) oligomer supported N-heterocyclic carbene ruthenium complex 1 as a recyclable ring-closing metathesis (RCM) catalyst was described. The polymeric complex 1 exhibited thermomorphic solubility, ­being insoluble in toluene at 25 ˚C and soluble at 65 ˚C. The homogeneous RCM with 1 was performed in toluene at 65 ˚C, and cooling to 25 ˚C led to precipitation of 1. The reaction system afforded quantitative products with high recyclability.