Cyclopentadienyl Ruthenium Research Articles

Engineering and Performance of Ruthenium Complexes Immobilized on Mesoporous Siliceous Materials as Racemization Catalysts

Dynamic kinetic resolution (DKR) is one of the most attractive routes to enantioselective synthesis, and ruthenium complexes are often applied as racemization catalysts. Two substituted cyclopentadienyl ruthenium complexes were immobilized covalently and non-covalently on mesoporous silica of mesocellular foam (MCF) and Santa Barbara Amorphous (SBA)-15 type functionalized with a 3 carbon spacer and 4-(chloromethyl)-N-amidobenzoate moiety. The catalysts were studied in a model reaction of secondary alcohol racemization. The immobilization decreased catalyst activity, considerably more for SBA-15 than for MCFs, and complete racemization of 1-phenylethanol was achieved within 24 h with the MCF-supported catalyst. The catalyst could be recovered and reused, thus paving the way for further development of the DKR process. The synthesized materials were fully characterized by Fourier-transform infrared spectroscopy analysis, thermogravimetry analysis, inductively cou-pled plasma optical emission spectrometry, and nitrogen adsorption at 77 K.

Desymmetrised pentaporphyrinic gears mounted on metallo-organic anchors.

Mastering intermolecular gearing is crucial for the emergence of complex functional nanoscale machineries. However, achieving correlated motion within trains of molecular gears remains highly challenging, due to the multiple degrees of freedom of each cogwheel. In this context, we designed and synthesised a series of star-shaped organometallic molecular gears incorporating a hydrotris(indazolyl)borate anchor to prevent diffusion on the surface, a central ruthenium atom as a fixed rotation axis, and an azimuthal pentaporphyrinic cyclopentadienyl cogwheel specifically labelled to monitor its motion by non-time-resolved Scanning Tunneling Microscopy (STM). Desymmetrisation of the cogwheels was first achieved sterically, i.e. by introducing one tooth longer than the other four. For optimal mechanical interactions, chemical labelling was also investigated as a preferential way to induce local contrast in STM images, and the electronic properties of one single paddle were modulated by varying the porphyrinic scaffold or the nature of the central metal. To reach such a structural diversity, our modular synthetic approach relied on sequential cross-coupling reactions on a penta(p-halogenophenyl)cyclopentadienyl ruthenium(ii) key building block, bearing a single pre-activated p-iodophenyl group. Chemoselective Sonogashira or more challenging Suzuki–Miyaura reactions allowed the controlled introduction of the tagged porphyrinic tooth, and the subsequent four-fold cross-couplings yielded the prototypes of pentaporphyrinic molecular gears for on-surface studies, incorporating desymmetrised cogwheels over 5 nm in diameter.

Cyclopentadienyl ruthenium(II) carbosilane metallodendrimers as a promising treatment against advanced prostate cancer

In searching for efficient and selective antitumour drugs, a new family of carbosilane metallodendrimers functionalized with [Ru(η5-C5H5)(PTA)Cl] (PTA = 1,3,5-triaza-7-phosphatricyclo-[3.3.1.1] decane) is reported. Experiments of the biophysical characterization showed an ability to interact with biological membranes, as well as with proteins (e.g. human serum albumin) without affecting their usual biological activity. These metallodendrimers possessed potent and selective anticancer activity in vitro in a panel of tumour cell lines. Importantly, the first generation metallodendrimer, bearing 4 Ru(II) complexes, was remarkably active towards resistant prostate cancer cells, inhibiting both cell proliferation and metastasis to bone tissues. Such promising antitumour activity can be further improved when given with docetaxel, with in vitro cytotoxicity being in the nanomolar range. Furthermore, its intravenous administration to an advanced prostate cancer mice model inhibited tumour growth up to 25% and 45% when given 10 mg/kg/week and 7.5 mg/kg/4–5 days, respectively.

Synthesis and Reactivity of Cyclopentadienyl Ruthenium(II) Complexes with Tris(alkylthio)benzenes: Transformation between Dinuclear and Sandwich-Type Complexes.

To explore the structural transformation of cyclopentadienyl ruthenium (CpRu) complexes in response to external stimuli, the reaction of [RuCp(MeCN)3][X] (X = PF6, (FSO2)2N [= FSA]) and tris(alkylthio)benzenes (1,3,5-C6H3(SR)3; L1: R = Pr, L2: R = Me) was investigated, and the crystal structures and thermal properties of the products were examined. The reaction produced the sandwich complexes [RuCpLn][X] or dinuclear complexes [Ru2Cp2(μ-Ln)2(CH3CN)m][X]2 (X = PF6, FSA) depending on the reaction conditions. The sandwich complex [RuCpL1][FSA] was an ionic liquid. The solids of dinuclear complexes transformed into the thermodynamically stable sandwich complexes upon heating accompanied by acetonitrile loss. This change resulted in a transformation from crystal to ionic liquid for complexes with the FSA anion. UV irradiation of the sandwich complex [RuCpL1][PF6] in methanol produced the dinuclear complex [Ru2Cp2(μ-L1)2L12][PF6]2. The complex transformed into the sandwich complex upon heating.

Synthesis of an optically active polymer containing a planar phthalimide backbone by asymmetric polymerization

Herein we present the precise design and synthesis of a novel polymer backbone that induces a helical structure through asymmetric polymerization reactions of a phthalimide-based monomer catalyzed by a planar-chiral cyclopentadienyl–ruthenium complex.

Reversible detection of phosphorylation and dephosphorylation by tip-enhanced Raman spectroscopy using a cyclopentadienyl ruthenium nanotag functionalized tip.

The detection of cancer invasion is crucial for diagnosis. In this report, we employed a TERS tip and SERS nanotags to create a cell signaling based nano-sensing system. This system is capable of creating a reversible phosphorylation/de-phosphorylation cycle for TERS measurement. The reversible TERS sensing is then paired with a downstream binding domain, Src homology region 2 (SH2), which is associated with the cell signaling for cancer cell invasion. Such a system offers the advantages of convenient detection of nanotags and high sensitivity as validated in a cell model.

Star-Shaped Ruthenium Complexes as Prototypes of Molecular Gears.

The design and synthesis of two families of molecular-gear prototypes is reported, with the aim of assembling them into trains of gears on a surface and ultimately achieving controlled intermolecular gearing motion. These piano-stool ruthenium complexes incorporate a hydrotris(indazolyl)borate moiety as tripodal rotation axle and a pentaarylcyclopentadienyl ligand as star-shaped cogwheel, equipped with five teeth ranging from pseudo-1D aryl groups to large planar 2D paddles. A divergent synthetic approach was followed, starting from a pentakis(p-bromophenyl)cyclopentadienyl ruthenium(II) complex as key precursor or from its iodinated counterpart, obtained by copper-catalyzed aromatic Br/I exchange. Subsequent fivefold cross-coupling reactions with various partners allowed high structural diversity to be reached and yielded molecular-gear prototypes with aryl-, carbazole-, BODIPY- and porphyrin-derived teeth of increasing size and length.

Cyclopentadienyl Ruthenium(II) Complex-Mediated Oxidation of Benzylic and Allylic Alcohols to Corresponding Aldehydes

This work reports an efficient method for the oxidation reaction of aliphatic, aromatic allylic, and benzylic alcohols into aldehydes catalyzed by the cyclopentadienyl ruthenium(II) complex (RuCpCl(PPh3)2) with bubbled O2. Through further optimizing controlled studies, the tendency order of oxidation reactivity was determined as follows: benzylic alcohols > aromatic allylic alcohols >> aliphatic alcohols. In addition, this method has several advantages, including a small amount of catalyst (0.5 mol%) and selective application of high discrimination activity of aliphatic, aromatic allylic, and benzylic alcohols.

Efficient transfer of dithiolene ligands from nickel to cyclopentadienyl ruthenium complexes

The reaction of [CpRu(PPh3)2Cl] with [Ni(S2C2Ph2)2] in refluxing toluene produces the purple salt [CpRu(S2C2Ph2)(PPh3)][Cl], containing a rare example of a cationic dithiolene complex, in excellent yield. Chemical or electrochemical reduction of [CpRu(S2C2Ph2)- (PPh3)][Cl] causes a colour change to blue and formation of the corresponding neutral species [CpRu(S2C2Ph2)(PPh3)]. In contrast the reaction of [CpRu(CO)2Cl] with [Ni(S2C2Ph2)2] under similar conditions was unsuccessful, but dithiolene transfer could be induced at room temperature by the use of Me3NO as a decarbonylating agent. In this case the neutral paramagnetic complex [CpRu(S2C2Ph2)(CO)] was formed, together with a crystallographically characterised dinuclear compound [Ru2(μ-S2C2Ph2)(μ-CO)(CO)Cp2]. The different outcomes of these reactions are related to the σ-donor and π-acceptor properties of the ligands.

Cyclopentadienyl ruthenium complexes of mixed heterocyclic thiol and Bis(diphenylphosphino)ferrocene ligands

Cyclopentadienyl ruthenium complexes bearing mixed heterocyclic thiol and bis(diphenylphsphino)ferrocene (dppf) ligands are presented. The complex-salts [CpRu(dppf)(κ1S-HS-het)]PF6 {Cp = η5-C5H5; HS-het = 2-mercaptobenzothiazole (1), 2-mercaptobenzimidazole (2)} were synthesized from the reaction of CpRu(dppf)Cl with the thiol in the presence of KPF6 salt under reflux. Complexes 1 and 2 have been characterized by spectroscopic methods (1H-NMR, 31P{1H}-NMR, MS) and elemental analysis. The solid-state structures of [CpRu(dppf)(κ1SS2C7H5N)]PF6 (1) and [CpRu(dppf)(κ1S-SC7H6N2)]PF6 (2) have been determined by X-ray crystallography. The cyclic voltammetry of these two complexes are measured.

Expedient Synthesis of Thioether‐Functionalized Hydrotris(indazolyl)borate as an Anchoring Platform for Rotary Molecular Machines

Major improvements in the synthesis of surface‐mounted rotary molecular machines based on ruthenium(II) complexes are reported. The development of a one‐pot indium(III)‐mediated “N‐deprotection/ester reductive sulfidation” sequence allowed step economy, reproducibility and high efficiency in the synthesis of the thioether‐functionalized tripodal ligand. Switching to the thallium salt of hydrotris(indazolyl)borate and to microwave heating further optimized the preparation of the common intermediate in the modular synthesis of symmetric and dissymmetric molecular motors and gears. The penta(4‐bromophenyl)cyclopentadienyl ruthenium(II) key precursor is now reproducibly synthesized in 5 steps and 31 % overall yield on the longest linear sequence. Subsequent fivefold Suzuki–Miyaura coupling with ferroceneboronic acid led to a new C5‐symmetric pentaferrocenyl molecular motor.

Hydrophosphonylation of aldehydes catalyzed by cyclopentadienyl ruthenium(II) complexes

This work reports the first method for the synthesis of α-hydroxyphosphonates from aldehydes catalyzed by cyclopentadienyl ruthenium(II) complexes. The best results were obtained using the system HP(O)(OEt)2/[RuClCp(PPh3)2] (5 mol%), affording the α-hydroxyphosphonates in good to excellent yields with high chemoselectivity. The catalyst [RuClCp(PPh3)2] can be used for at least 12 catalytic cycles with excellent activity and the reactions were carried out under solvent free conditions. DFT calculations were performed to rationalize the mechanism showing that the barriers associated with the H-phosphonate tautomer, HP(O)(OR)2 are unrealistically high. This led us to propose that the catalyst promotes the tautomerization towards phosphite, P(OH)(OR)2, via P-atom coordination, which accounts for the observed reactivity.

Direct Aminophosphonylation of aldehydes catalyzed by cyclopentadienyl ruthenium(II) complexes

This work reports a novel method for the direct aminophosphonylation of aldehydes catalyzed by cyclopentadienyl ruthenium(II) complexes. The system HP(O)(OEt)2/[CpRu(PPh3)2Cl] was very efficient for the aminophosphonylation of aldehydes with primary and secondary amines, producing the corresponding α-aminophosphonates in good to excellent yields. This novel method has several advantages including the use of a small amount of catalyst (0.5 mol%), high chemoselectivity, solvent-free conditions and application of the catalyst [CpRu(PPh3)2Cl] for at least 12 cycles with excellent activity.

Synthesis, characterization, and anticancer activity of dithiocarbamate ruthenium(II) complexes

GRAPHICAL ABSTRACT

Chiral Cyclopentadienyl Ruthenium Complexes as Versatile Catalysts for Enantioselective Transformations.

Ruthenium complexes, in particular cyclopentadienyl ruthenium (<small>ii</small>) derivatives, catalyze a vast number of transformations in the field of homogenous catalysis. Herein we describe the first synthesis of efficient chiral cationic cyclopentadienyl ruthenium (<small>ii</small>) catalysts and their application in enantioselective cycloisomerizations yielding 4H-pyrans. A tremendous counterion effect on the selectivity was observed and subsequently explored, giving rise to a complementary set of neutral cyclopentadienyl ruthenium (<small>ii</small>) complexes able to catalyze asymmetric cyclobutene formations.

Morphological and in vitro evaluation of programmed cell death in MCF-7 cells by new organoruthenium(ii) complexes

Cyclopentadienyl ruthenium(ii) thiosemicarbazone complexes with the formula [Ru(η5-C5H5)(Ac-tsc)PPh3]·Cl (1), [Ru(η5-C5H5)(Ac-mtsc)PPh3]·Cl (2), [Ru(η5-C5H5)(Ac-etsc)PPh3]·Cl (3) and [Ru(η5-C5H5)(Ac-ptsc)PPh3] (4) were synthesized and characterized by various spectroscopic techniques (1H NMR,13C NMR, IR and UV-vis).

Ruthenium Lewis Acid‐Catalyzed Asymmetric Diels–Alder Reactions: Reverse‐Face Selectivity for α,β‐Unsaturated Aldehydes and Ketones

Acrolein, methacrolein, methyl vinyl ketone, ethyl vinyl ketone, 3‐methyl‐3‐en‐2‐one, and divinyl ketone were coordinated to a cationic cyclopentadienyl ruthenium(II) Lewis acid incorporating the electron‐poor bidentate BIPHOP–F ligand. Analysis by NOESY and ROESY NMR techniques allowed the determination of conformations of enals and enones present in solution in CD2Cl2. The results were compared to solid‐state structures and to the facial selectivities of catalytic asymmetric Diels–Alder reactions with cyclopentadiene. X‐Ray structures of four Ru‐enal and Ru‐enone complexes show the α,β‐unsaturated C=O compounds to adopt an anti‐s‐trans conformation. In solution, enals assume both anti‐s‐trans and anti‐s‐cis conformations. An additional conformation, syn‐s‐trans, is present in enone complexes. Enantioface selectivity in the cycloaddition reactions differs for enals and enones. Reaction products indicate enals to react exclusively in the anti‐s‐trans conformation, whereas with enones, the major product results from the syn‐s‐trans conformation. The alkene in s‐cis conformations, while present in solution, is shielded and cannot undergo cycloaddition. A syn‐s‐trans conformation is found in the solid state of the bulky 6,6‐dimethyl cyclohexanone‐Ru(II) complex. The X‐ray structure of divinyl ketone is unique in that the Ru(II) center binds the enone via a η2 bond to one of the alkene moieties. In solution, coordination to Ru–C=O oxygen is adopted. A comparison of facial preference is also made to the corresponding indenyl Lewis acids.

A Long-Lived Mononuclear Cyclopentadienyl Ruthenium Complex Grafted onto Anatase TiO2 for Efficient CO2 Photoreduction.

This work shows a novel artificial donor-catalyst-acceptor triad photosystem based on a mononuclear C5 H5 -RuH complex oxo-bridged TiO2 hybrid for efficient CO2 photoreduction. An impressive quantum efficiency of 0.56 % for CH4 under visible-light irradiation was achieved over the triad photocatalyst, in which TiO2 and C5 H5 -RuH serve as the electron collector and CO2 -reduction site and the photon-harvester and water-oxidation site, respectively. The fast electron injection from the excited Ru(2+) cation to TiO2 in ca. 0.5 ps and the slow backward charge recombination in half-life of ca. 9.8 μs result in a long-lived D(+) -C-A(-) charge-separated state responsible for the solar-fuel production.

ChemInform Abstract: Enantio‐ and Diastereoselective Asymmetric Allylic Alkylation Catalyzed by a Planar‐Chiral Cyclopentadienyl Ruthenium Complex.

AbstractThe mild reaction conditions result in the formation of chiral diketones having two vicinal stereocenters.

A heterogeneous mesoporous silica-supported cyclopentadienyl ruthenium(II) complex catalyst for selective hydrosilylation of 1-hexyne at room temperature

A cyclopentadienyl ruthenium(II) complex has been immobilized on MCM-41 modified with aminopropyl group through an amide bond formation reaction. FT-IR and UV–vis spectra show successful immobilization of cyclopentadienyl ruthenium complex onto the mesoporous silica surface by utilizing the amino group as a connector. The coordination state of the ruthenium complex is analyzed in detail by XAFS measurements, which indicate that the immobilization process does not influence its coordination geometry. Moreover, the retaining of long range ordering of the mesoporous structure of MCM-41 after grafting is evident from the results of XRD and N2 adsorption–desorption measurements. The resulting material promotes efficiently the hydrosilylation of 1-hexyne to produce vinylsilane with high α-selectivity under UV-irradiation at room temperature. Furthermore, the catalyst is recyclable for several catalytic runs without significant loss of its catalytic activity.