Ru Carbene Complex Research Articles

Triazole-modified Ru-carbene complexes: A valid olefin metathesis pre-catalyst for dynamic covalent chemistry via C=C bond formation

The 1,2,3-triazole coordinated ruthenium carbene complexes (TA-Ru) were reported for the first time as a new class of modified Grubbs catalyst to achieve challenging olefin metathesis at higher temperatures without catalyst decomposition. Previously reported N-tethered Ru-carbene complexes all suffered from rapid cis/trans isomerization, causing significantly reduced catalyst reactivity. These new TA-Ru complexes hold the active trans-dichloro conformation even at 80 °C, allowing effective olefin metathesis for challenging substrates. With this new TA-Ru catalyst, cross-metathesis (CM), ring-closing metathesis (RCM) and dynamic covalent chemistry (DCvC) were achieved. Excitingly, the reactivity of TA-Ru prevails all previously reported N-coordinated Ru-carbene precatalysts, Grubbs II, and Hoveyda-Grubbs, making the TA-Ru a transformative catalytic system in olefin catalysis.

ONE-POT SYNTHESIS OF NORBORNENE-CYCLOOCTENE COPOLYMERS

The one-pot synthesis of random multiblock copolymers of norbornene and cyclooctene has been performed for the first time. It is shown that the first generation Grubbs Ru-carbene complex makes it possible to obtain these copolymers directly from monomers. In the course of one-pot synthesis, the metathesis polymerization of norbornene, which has a markedly higher ring strain, occurs first. Then, cyclooctene polymerizes and simultaneously an interchain cross-metathesis reaction takes place, during which the block structure of the copolymer is formed. Compared to the previously studied interaction of polynorbornene and polycyclooctene, the one-pot method makes it possible to obtain copolymers with a higher molar mass at a lower catalyst consumption.

Synthesis of N-Arylindoles from 2-Alkenylanilines and Diazonaphthalen-2(1H)-ones through Simultaneous Indole Construction and Aryl Introduction.

In this paper, an efficient synthesis of N-arylindoles through the cascade reaction of 2-alkenylanilines with diazonaphthalen-2(1H)-ones is presented. Mechanistically, this reaction involves the generation of a Ru-carbene complex from diazonaphthalen-2(1H)-one, followed by carbene N-H bond insertion with 2-alkenylaniline, intramolecular cyclization, and oxidative aromatization. In this reaction, the Ru(II) complex acts as a multifunctional catalyst to promote not only the carbene formation but also the intramolecular cyclization and the dehydrogenative aromatization. Meanwhile, air acts as a green and cost-effective oxidant. To our knowledge, this is the first example in which N-arylindoles were synthesized through simultaneous introduction of the N-aryl unit and construction of the indole scaffold. Notable advantages of this method include readily accessible and halide-free substrates, additive-free reaction conditions, good efficiency, excellent atom economy, and compatibility with diverse functional groups. In addition, the utility of the product thus obtained was showcased by its diverse structural transformations.

A Semiconductor-Mediator-Catalyst Artificial Photosynthetic System for Photoelectrochemical Water Oxidation.

In fabricating an artificial photosynthesis (AP) electrode for water oxidation, we have devised a semiconductor-mediator-catalyst structure that mimics photosystem II (PSII). It is based on a surface layer of vertically grown nanorods of Fe2 O3 on fluorine doped tin oxide (FTO) electrodes with a carbazole mediator base and a Ru(II) carbene complex on a nanolayer of TiO2 as a water oxidation co-catalyst. The resulting hybrid assembly, FTO|Fe2 O3 |-carbazole|TiO2 |-Ru(carbene), demonstrates an enhanced photoelectrochemical (PEC) water oxidation performance compared to an electrode without the added carbaozle base with an increase in photocurrent density of 2.2-fold at 0.95 V vs. NHE and a negatively shifted onset potential of 500 mV. The enhanced PEC performance is attributable to carbazole mediator accelerated interfacial hole transfer from Fe2 O3 to the Ru(II) carbene co-catalyst, with an improved effective surface area for the water oxidation reaction and reduced charge transfer resistance.

Cyclododecene in Olefin Metathesis: Polymerization and Macromolecular Cross-Metathesis with Polynorbornene

The reaction of macromolecular cross-metathesis of polynorbornene and polydodecenamer catalyzed by the first-generation Grubbs Ru-carbene complex is studied for the first time. Polydodecenamer with high-molecular-weight characteristics (Mw = 406 × 103, Ð = 2.5) and a yield of 96% is synthesized by the ring-opening metathesis polymerization of cyclododecene mediated by the second-generation Grubbs catalyst. The polymer has a melting temperature of 62–83°C, depending on the content of trans double bonds, and shows poor solubility in organic solvents at room temperature. Its cross-metathesis with polynorbornene at 40°С gives rise to new statistical multiblock copolymers of norbornene and cyclododecene with different degree of blockiness. NMR, GPC, and DSC were used to investigate the effect of reaction conditions on the structure and thermal properties of the copolymers. At the initial step of the reaction, along with a high-molecular-weight peak, the GPC chromatograms exhibit a peak due to the low-molecular-weight fraction (M = (1–2) × 103), suggesting the formation of cyclooligomers. With increasing degree of interchain exchange, the proportion of the oligomeric fraction decreases appreciably. The kinetics of the cross-metathesis of polynorbornene with polydodecenamer and polyoctenamer at 40°С is studied by in situ 1Н NMR spectroscopy and ex situ 13С NMR spectroscopy. The rates of elementary reactions in these blends differ insignificantly, except for the conversion stage of the initial carbenes into polymer ones. The formation rate for carbene [Ru]=polyoctenamer is three times higher than the formation rate for the [Ru]=polydodecenamer carbene. In both cases, the fraction of Ru carbenes attached to norbornene units is extremely small throughout the process.

Cross-Metathesis and Hydrogenation in Polynorbornene–Poly(5-hydroxyoctenamer) Mixture in the Presence of Grubbs’ Catalysts

An exchange reaction of cross-metathesis between polynorbornene and poly(5-hydroxyoctenamer) in a chloroform–methanol mixture (10: 1 vol/vol) in the presence of Ru–carbene Grubbs’ complexes Gr-1 and Gr-2 has been studied. Gr-2 catalyst has a much higher activity and allows one to obtain multiblock copolymers, which cannot be synthesized directly from norbornene and 5-hydroxy-1-cyclooctene. The average length of the copolymer blocks varies in a wide range depending on the reaction conditions. The individual stages of the process have been studied with the use of in situ monitoring of transformations of Ru–carbene complexes by 1Н NMR spectroscopy and ex situ analysis of heterodyad evolution in copolymers via 13C NMR spectroscopy. As has been shown, poly(5-hydroxyoctenamer) forms Ru–carbene complexes with the catalyst more easily than polynorbornene; in this case, the incorporation of a substituent in the monomer unit of octenamer retards the polymer cross-metathesis. It has been found that, in systems containing Gr-2 and hydroxyoctenamer blocks, the formed ruthenium hydride complexes initiated hydrogenation process. The hydrogenation results in the appearance of crystallinity in the initially amorphous polymers, which opens up the possibilities for the targeted control of the multiblock copolymers properties.

Olefin-tethered organoruthenium carbene complexes: Synthesis, X-ray structure and catalytic insights on hydrogenation of esters

A series of Ru(II) complexes encompassing imidazolylidene olefin arm have been designed. The newly synthesized ligands and complexes were fully characterized by 1H, 13C NMR, and elemental analyses. Structural geometry for one of the envoy Ru(II) carbene complexes 3a was confirmed by single-crystal X-ray diffraction studies. The complexes acquired a distorted octahedral geometry. The highly active [Ru(II)-NHC] complex 3b, showed excellent catalytic performance for the hydrogenation of esters in 1,4-dioxane medium. The effects of solvent, base, wingtip substituents, time and catalyst loading were also investigated. The reported catalyst performed exceptionally well for a range of esters and furnishes very good yield of hydrogenated products.

Conformational Control of Initiation Rate in Hoveyda–Grubbs Precatalysts

When the coordinating isopropyl ether of the Hoveyda precatalyst is replaced by a cyclohexyl ether, it is possible to control the substituent’s conformation in either the equatorial or axial position. A stereodivergent synthesis of axial and equatorial cyclohexyl vinyl ethers provided access to new ruthenium metathesis precatalysts by carbene exchange. The conformational disposition of the coordinating aryl ether was found to have a significant effect on the reactivity of the precatalyst in alkene metathesis. The synthesis of four new Ru carbene complexes is reported, featuring either the 1,3-bis(2,4,6-trimethylphenyl)dihydroimidazolylidene (H2IMes) or the 1,3-bis(2,6-diisopropylphenyl)dihydroimidazolylidene (SIPr) N-heterocyclic carbene ligand. The conformational isomers in the SIPr series were structurally characterized. Performance testing of all new precatalysts in three different ring-closing metatheses and an alkene cross metathesis illustrated superior performance by the precatalysts bearing axial coordinating ethers. Initiation rates with butyl vinyl ether were also measured, providing a useful comparison to existing Hoveyda-type metathesis precatalysts. Use of conformational control of the coordinating ether substituent provides a new way to modulate reactivity in this important class of alkene metathesis precatalysts.

Synthesis of new multiblock copolymers via cross-metathesis reaction of polytrimethylsilylnorbornene and polycyclooctene

The cross-metathesis reaction between polytrimethylsilylnorbornene and polycyclooctene is investigated for the first time. Using the Grubbs Ru-carbene complex of the first generation, the synthesis of random multiblock copolymers of trimethylsilylnorbornene and cyclooctene is carried out. The effect of the reaction conditions on the block length and thermal and crystalline properties of new copolymers is studied by NMR, GPC, and DSC methods. With the use of in situ 1Н NMR spectroscopy, the kinetics of the crossmetathesis reaction is investigated. As for unsubstituted polynorbornene (Polym. Sci., Ser. B 58, 292 (2016)), the catalyst interacts initially with polycyclooctene, giving a polymer carbene complex [Ru]=PCO. Further, this complex attacks the polytrimethylsilylnorbornene chain via cross reaction with formation of complex [Ru]=PNB-Si and a diblock copolymer of trimethylsilylnorbornene and cyclooctene as reaction products. The subsequent cross reactions form a multiblock copolymer with gradually increasing block length. Throughout the entire process, the concentration of [Ru]=PCO exceeds the concentration of [Ru]=PNB-Si by more than two orders of magnitude. Simultaneously, the total concentration of carbene complexes decreases in time through their decay. The reaction kinetics is satisfactorily described by a model proposed previously for interaction between polycyclooctene and polynorbornene.

Controlling Coordination Geometries: Ru-Carbene Complexes with Tetra-NHC Ligands.

The synthesis of the first ruthenium(II) complexes bearing open-chain tetra-N-heterocyclic carbene (tetra-NHC) ligands via in situ transmetalation is described. The ruthenium complexes show differing coordination geometries depending on the length of the alkyl linker. Replacement of the two cis acetonitrile ligands in the methylene bridged ruthenium complex by nucleophiles also influences the coordination geometry. Both structural motifs were evaluated in transfer hydrogenation (TH) of acetophenone, and in particular the sawhorse-type coordinated system exhibits remarkable activity with turnover frequencies of more than 100 000 h(-1).

Ring-Closing Metathesis with an Ionic MNP-Supported Ru–Carbene Complex

Key words magnetic nanoparticles - ring-closing metathesis - heterogeneous catalysis - ruthenium

Imidazolium‐Salt‐Functionalized Ionic‐CNT‐Supported RuCarbene/Palladium Nanoparticles for Recyclable Tandem Metathesis/Hydrogenation Reactions in Ionic Liquids

NP and tuck: Two different catalysts, a Ru-carbene complex and palladium nanoparticles, were immobilized onto the same imidazolium-salt-functionalized ionic CNTs. These supported dual-function catalysts showed excellent catalytic activity in tandem metathesis/hydrogenation reactions in an ionic liquid and could be recovered and reused four times. RCM = ring-closing metathesis.

Ring-Closing Metathesis of Dienes with a Supported Ru-Carbene Complex

Ring-Closing Metathesis of Dienes with a Supported Ru-Carbene Complex

Ionic CNT-supported Ru–carbene complex for recyclable ring-closing metathesis

The ionic multi-walled carbon nanotubes (IM-f-MWCNTs), which were covalently functionalized with imidazolium salt, have been utilized as support materials for the immobilization of Hoveyda-type Ru–carbene complex. The catalytic activity and recyclability of the ionic CNT-supported Ru–carbene complexes have been investigated for ring-closing metathesis of various dienes, and the recovered catalyst can be reused up to 10 times without any significant loss of catalytic activity.

A phase‐separable second‐generation hoveyda‐grubbs catalyst for ring‐opening metathesis polymerization

AbstractPolyisobutylene‐supported second‐generation Hoveyda‐Grubbs catalyst is shown to be an effective nonpolar phase tag for ring‐opening metathesis polymerization (ROMP). The catalytic activities of the supported Ru–carbene complex in ROMP are comparable to those of their homogeneous counterparts. The separability of these catalysts leads to lower Ru contamination (0.5 ppm levels) in the polymer products in comparison to the nonsupported Hoveyda‐Grubbs catalyst (10 PPM). © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

Copolymerization of 5-(trimethylsilyl)norbornene and 5-ethylidene-2-norbornene

Addition and metathesis copolymerization of 5-(trimethylsilyl)norbornene (TMSNB) and 5-ethylidene-2-norbornene (ENB) has been studied. High-molecular-weight metathesis copolymers have been obtained on the first-generation Grubbs catalyst based on the Ru carbene complex Cl2Ru(=CHPh)(PCy3)2 with nearly quantitative yields. Addition copolymerization has been carried out on the Ni(II) naphthenatemethylaluminoxane (MAO) catalytic system. In both cases copolymerization proceeded without participation of ethylidene double bond. Copolymers of this type are promising ones for manufacturing stable highly permeable polymeric membranes, since they are capable for crosslinking.

‘Hemilabile’ silyl pincer ligation: platinum group PSiN complexes and triple C–H activation to form a (PSiC)Ru carbene complex

The first example of PSiN mixed-donor silyl pincer ligation is described. Studies involving platinum group metal complexes of [(2-(t)Bu(2)PC(6)H(4))(2-Me(2)NC(6)H(4))SiMe](-) ((t)Bu-PSiN-Me) confirmed that the ligand amino donor is labile. Within the coordination sphere of Ru, (t)Bu-PSiN-Me is transformed into a PSiC ligand via multiple C-H bond activation events.

Synthesis of High Molecular Weight Poly[3-{tris(trimethylsiloxy)silyl}tricyclononenes-7] and Their Gas Permeation Properties

N and its derivatives can be polymerized, producing high molecular weight products of entirely different structure of the main chain depending on the choice of the catalysts. In the presence of the catalysts such as WCl6, RuCl3, Re2O7/Al2O3, or Grubbs Ru carbene complexes, ring-opening metathesis polymerization (ROMP) proceeds leading to formation of cyclolinear unsaturated polymers. On the other hand, norbornenes can be also polymerized via opening of double bonds like vinyl monomers in the presence of Ni and Pd catalysts. This addition-type polymerization leads to bulky bicyclic repeat units that do not contain unsaturated bonds. Most of the ROMP polynorbornenes are glassy polymers (Tg in the range ca. 40 100 C) with relatively small gas permeability (P(O2) = 1 100 barrer). However, introduction of silicon-containing substituents in monomer units significantly increases this parameter. Addition-type polynorbornenes have rigid main chains, their glass transition temperatures in most cases are above the onset of thermal decomposition (>400 C), and those that contain bulky Me3Si groups are characterized by much higher gas permeability (P(O2) = 90

Ruthenium carbene complexes containing bidentate and tridentate P [dbnd]O ligands

Treatment of [Ru( CHR)Cl 2(PCy 3) 2] (Cy = cyclohexyl) with Tl[N(Pr 2 iPO) 2] and AgL OEt (L OEt − = [CpCo{P(O)(OEt) 2} 3] −) afforded the Ru carbene complexes [Ru( CHPh)(PCy 3)Cl{N(Pr 2 iPO) 2}] ( 1) and [L OEtRu( CHR)(PCy 3)Cl] ( 2), respectively. Chloride abstraction of complex 2 with TlPF 6 in MeCN afforded [L OEtRu( CHPh)(PCy 3)(MeCN)][PF 6] ( 3). Complexes 1 and 2 are capable of catalyzing ring-closing metathesis of diethyl 1,2-diallylmalonate. The crystal structure of complex 2 has been determined.

Synthesis, structure and electrochemical behaviour of Ru(ii)- and Pt(ii)-carbene complexes of the NCN-pincer 1,3-bis(2-pyridylmethyl)-1H-benzimidazolium chloride

Novel NCN-pincer carbene complexes of Ru(II), 1,3-bis(2-pyridylmethyl)benzimidazolineruthenium(II) bishexafluorophosphate (2), and Pt(II), 1,3-bis(2-pyridylmethyl)benzimidazolinechloroplatinum(II) hexafluorophosphate (3), complexes based on 1,3-bis(2-pyridylmethyl)-1H-benzimidazolium chloride (1) were synthesized and characterized by different spectroscopic methods. Complex 2 shows an absorption maximum at 386 nm, blue-shifted in comparison to Ru(bpy)32+ and Ru(tpy)22+, probably due to the strong σ-donor and weak π-acceptor properties of the electron-rich NHC ligand. Electrochemical studies show Ru(II)/Ru(III) and Pt(II)/Pt(IV) reversible couples at 0.67 and 0.58 eV, respectively, lower than those for the analogous complexes of ligands like bipyridine (bpy), terpyridine (tpy) and phenylbipyridine (pbpy). The solid state structure of 2 was solved by X-ray diffraction. Theoretical studies (B3LYP/LANL2DZ) of the complex show a HOMO (−0.38594 au) mainly centered on the ruthenium and benzimidazole, whereas the LUMO (−0.25130 au) is populated by pyridines. Therefore, it is assumed that the charge transfer from HOMO → LUMO is mixed ILCT (interligand charge transfer)/MLCT (metal to ligand charge transfer). The observed lower redox potentials of the Pt(II) complex compared to the Ru(II) complex is supported by theoretically calculated ionisation potentials and also electron affinity values. To the best of our knowledge, 2 is the first example of a six-membered metallacycle homoleptic chelate pincer NCN–Ru(II) N-heterocyclic carbene complex.