Catalyst RuCl2 Research Articles

The Impact of Water on Ru-Catalyzed Olefin Metathesis: Potent Deactivating Effects Even at Low Water Concentrations.

Ruthenium catalysts for olefin metathesis are widely viewed as water-tolerant. Evidence is presented, however, that even low concentrations of water cause catalyst decomposition, severely degrading yields. Of 11 catalysts studied, fast-initiating examples (e.g., the Grela catalyst RuCl2(H2IMes)(=CHC6H4-2-OiPr-5-NO2) were most affected. Maximum water tolerance was exhibited by slowly initiating iodide and cyclic (alkyl)(amino)carbene (CAAC) derivatives. Computational investigations indicated that hydrogen bonding of water to substrate can also play a role, by retarding cyclization relative to decomposition. These results have important implications for olefin metathesis in organic media, where water is a ubiquitous contaminant, and for aqueous metathesis, which currently requires superstoichiometric “catalyst” for demanding reactions.

Challenging Metathesis Catalysts with Nucleophiles and Brønsted Base: Examining the Stability of State-of-the-Art Ruthenium Carbene Catalysts to Attack by Amines.

Critical to advancing the uptake of olefin metathesis in leading contexts, including pharmaceutical manufacturing, is identification of highly active catalysts that resist decomposition. Amines constitute an aggressive challenge to ruthenium metathesis catalysts. Examined here is the impact of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), morpholine, n-butylamine, and triethylamine on Ru metathesis catalysts that represent the current state of the art, including cyclic alkyl amino carbene (CAAC) and N-heterocyclic carbene (NHC) complexes. Accordingly, the amine-tolerance of the nitro-Grela catalyst RuCl2(H2IMes)(=CHAr) (nG; Ar = C6H4-2-OiPr-5-NO2) is compared with that of its CAAC analogues nGC1 and nGC2, and the Hoveyda-class catalyst RuCl2(C2)(=CHAr′) HC2 (Ar′ = C6H4-2-OiPr). In C1, the carbene carbon is flanked by an N-2,6-Et2C6H3 group and a CMePh quaternary carbon; in C2, by an N-2-iPr-6-MeC6H3 group and a CMe2 quaternary carbon. The impact of 1 equiv amine per Ru on turnover numbers (TONs) in ring-closing metathesis of diethyl diallylmalonate was assessed at 9 ppm Ru, at RT and 70 °C. The deleterious impact of amines followed the trend NEt3 ∼ NH2nBu ≪ DBU ∼ morpholine. Morpholine is shown to decompose nGC1 by nucleophilic abstraction of the methylidene ligand; DBU, by proton abstraction from the metallacyclobutane. Decomposition was minimized at 70 °C, at which nGC1 enabled TONs of ca. 60 000 even in the presence of morpholine or DBU, vs ca. 80 000 in the absence of base. Unexpectedly, H2IMes catalyst nG delivered 70–90% of the performance of nGC1 at high temperatures, and underwent decomposition by Brønsted base at a similar rate. Density functional theory (DFT) analysis shows that this similarity is due to comparable net electron donation by the H2IMes and C1 ligands. Catalysts bearing the smaller C2 ligand were comparatively insensitive to amines, owing to rapid, preferential bimolecular decomposition.

Transfer hydrogenation of ketones catalyzed by 2,6‐bis(triazinyl)pyridine ruthenium complexes: The influence of alkyl arms

The transfer hydrogenation of ketones catalyzed by transition metal complexes has attracted much attention. A series of ruthenium(II) complexes bearing 2,6-bis(5,6-dialkyl-1,2,4-triazin-3-yl)pyridine ligands (R-BTPs) were synthesized and characterized by NMR analysis and X-ray diffraction. These ruthenium(II) complexes were applied in the transfer hydrogenation of ketones. Their different catalytic activity were attributed to the alkyl arms on the 2,6-bis(5,6-dialkyl-1,2,4-triazin-3-yl)pyridine. As the length of the alkyl arms rising, the catalytic activities of the complex catalysts decreased. By means of 0.4 mol % catalyst RuCl2(PPh3)(3-methylbutyl-BTP) in refluxing 2-propanol, a variety of ketones were reduced to their corresponding alcohols with >95% conversion over a period of 3 h. © 2019 Elsevier Science. All rights reserved.

Synthesis and dynamic behaviour of a dimeric ruthenium benzylidene complex bearing a truncated N-heterocyclic carbene ligand

Described herein is the reaction of the first-generation Grubbs catalyst RuCl2(PCy3)2(=CHPh) (GI) with free IMe4 (1,3,4,5-tetramethylimidazol-2-ylidene), in which the N-mesityl groups commonly present in Ru-NHC metathesis catalysts are truncated to N-Me (NHC = N-heterocyclic carbene). Treatment of GI with IMe4 (1–2.1 equiv) effects displacement of both PCy3 ligands, but does not terminate at the mono-ruthenium species RuCl2(IMe4)2(=CHPh) Ru-3. Instead, dimerization occurs to afford [Ru2(μ-Cl)3(IMe4)4(=CHPh)2]Cl Ru-4, the structure of which was confirmed by crystallographic analysis. A molecular dynamics study of Ru-4 indicated rapid rotation of both the NHC and the benzylidene ligands, accounting for the observation of multiple benzylidene signals in the solution 1H NMR spectrum of Ru-4.

Formation of a Stable Complex, RuCl2(S2CPPh3)(PPh3)2, Containing an Unstable Zwitterion from the Reaction of RuCl2(PPh3)3 with Carbon Disulfide.

New insight into the complexity of the reaction of the prominent catalyst RuCl2(PPh3)3 with carbon disulfide has been obtained from a combination of X-ray diffraction and (31)P NMR studies. The red-violet compound originally formulated as a cationic π-CS2 complex, [RuCl(π-CS2)(PPh3)3]Cl, has been identified as a neutral molecule, RuCl2(S2CPPh3)(PPh3)2, which contains the unstable zwitterion S2CPPh3. In the absence of RuCl2(PPh3)3, there is no sign of a reaction between triphenylphosphine and carbon disulfide, although more basic trialkylphosphines form red adducts, S2CPR3. Despite the presence of an unstable ligand, RuCl2(S2CPPh3)(PPh3)2 is remarkably stable. It survives melting at 173-174 °C intact, is stable to air, and undergoes reversible electrochemical oxidation to form a monocation. When the reaction of RuCl2(PPh3)3 with carbon disulfide is conducted in the presence of methanol, crystals of orange [RuCl(S2CPPh3)(CS)(PPh3)2]Cl·2MeOH and yellow RuCl2(CS)(MeOH)(PPh3)2 also form. (31)P NMR studies indicate that the unsymmetrical dinuclear complex (SC)(Ph3P)2Ru(μ-Cl)3Ru(PPh3)2Cl is the initial product of the reaction of RuCl2(PPh3)3 with carbon disulfide. A path connecting the isolated products is presented.

On the Compatibility of Ruthenium Metathesis Catalysts with Secondary Phosphines

While attempts to incorporate secondary phosphine ligands into the first-generation Grubbs catalyst RuCl2(PR3)2(═CHPh) (GI, R = Cy) were frustrated by decomposition (for HPCy2) or bulk (for HPtBu2)...

Immobilization and Characterization of RuCl2(PPh3)3 Mesoporous Silica SBA-3

Abstract The five-fold coordinated ruthenium (II) catalyst RuCl2(PPh3)3 is heterogenized on the surface of amine functionalized mesoporous silica material SBA-3 and studied by BET, XRD and 31P CP-MAS solid-state NMR. The spectra indicate the replacement of one or two of the triphenyl-phosphine groups in the course of the grafting. To distinguish between both possibilities two-dimensional J-resolved 31P MAS solid-state NMR combined with quantum chemical calculations is employed. The changes of the scalar coupling pattern between the neat catalyst and the immobilized catalyst suggest the replacement of two of the PPh3-groups by coordinative bonds to the amine-functions of the linker. DFT calculations reveal the absence of two chemically and magnetically equivalent phosphines and confirm the replacement of two PPh3-groups. This finding is similar to the results observed for the binding of the rhodium in the Wilkinson's catalyst, despite the different coordination of the metals (four-fold versus five-fold), the presence of two chlorine ligands and the different transition metal.

Ruthenium(ii)-catalyzed selective monoarylation in water and sequential functionalisations of C–H bonds

The ruthenium(II)-phosphine catalyst RuCl2(PPh3)(p-cymene) operating water selectively leads to ortho monoarylation, with arylchlorides and heteroarylhalides, of functional arenes. Further catalytic heteroarylation with Ru(OAc)2(p-cymene) in water produces mixed bifunctional derivatives.

Reactions of Grubbs Catalysts with Excess Methoxide: Formation of Novel Methoxyhydride Complexes

On exposure to NaOMe (≥3 equiv) in CH2Cl2–MeOH at 23 °C, the first-generation Grubbs catalyst RuCl2(PCy3)2(═CHPh) (1a) is immediately transformed into the six-coordinate methoxyhydride complexes RuH(OMe)(CO)2(PCy3)2 (4a) and RuH(OMe)(CO)(H2)(PCy3)2 (5a). Complex 5a can be recycled into 4a under conditions conducive to removal of H2. The second-generation catalyst RuCl2(IMes)(PCy3)(═CHPh) (1b; IMes = N,N′-bis(mesityl)imidazol-2-ylidene) reacts more slowly, requiring several hours even at 20 equiv of NaOMe, and terminates at five-coordinate RuH(OMe)(CO)(IMes)(PCy3) (3b). Experiments in the presence of added PCy3 reveal that consumption of 1a, but not 1b, proceeds via the four-coordinate intermediate formed by equilibrium loss of phosphine, a function of the lability of the PCy3 ligand at ambient temperatures. The poor accessibility of such an intermediate for 1b at 23 °C retards salt metathesis and inhibits further reaction of 3b. For the bis(PCy3) analogue 3a, fast transformation into 4a is proposed to inv...

Alkylidene-Ruthenium-Tin Catalysts for the Formation of Fatty Nitriles and Esters via Cross-Metathesis of Plant Oil Derivatives

The reaction of SnCl2 with the Ru−Cl bond of the Grubbs I catalyst RuCl2(═CHPh)(PCy3)2 (1) gives the complex {[Ru(═CHPh)(SnCl3)(PCy3)]2(μ-Cl)3}−[HPCy3]+ (2), but containing two diethyl ether solvate molecules. The formal insertion of SnCl2 into one Ru−Cl bond of the Hoveyda II catalyst RuCl2(═CH-C6H4OPri)(H2IMes) (3) (H2IMes = N,N′-dimesityl-4,5-dihydroimidazol-2-ylidene) results in formation of the new complex RuCl(SnCl3)(═CH-C6H4OPri)(H2IMes) (4). The X-ray analyses of 2 and 4 show the presence of very short Ru−Sn bonds (2.5834(9) A mean bond for 2 and 2.5925(12) A for 4) and the retention of short Ru═C bonds (1.895(10) and 1.825(8) A, respectively). Complex 4 shows an excellent catalytic activity for the cross-metathesis of plant oil derivatives, the C11 ω-unsaturated ester and aldehyde and the unsaturated C18 diester with acrylonitrile, and a good activity for their cross-metathesis with methyl acrylate. Good to excellent yield of α,ω-bifunctional compounds, precursors of polyesters and polyamides, we...

Geometric and Electronic Structure of aC1-Symmetric Ruthenium-Aryloxide Metathesis Catalyst: An Experimental and Computational Study

Spectroscopic and computational methods were employed to establish the geometric and electronic structure of the Ru-pseudohalide metathesis catalyst RuCl(OC6Br5)(IMes)(py)(═CHPh) 5 (IMes = 1,3-dimesitylimidazol-2-ylidene, py = pyridine). NOESY-NMR and electronic absorption spectroscopic analysis of 5, carried out in parallel with analysis of the known trans- and cis-anionic structures RuCl2(IMes)(py)2(═CHPh) (3a) and Ru(o-cat)(IMes)(py)(═CHPh) 4a (o-cat = ortho-catecholate), confirms the trans-anionic geometry of the bromoaryloxide complex. An additional Ru···Br dative interaction is indicated by DFT analysis. The lower energy barrier to Ru−CNHC rotation vs N−CMes rotation is demonstrated for 4a and 5 and is suggested for the corresponding dichloride catalysts. The location and intensity of the principal visible absorption band is strongly conserved for 3a and 5a and is proposed as a useful signature to facilitate identification of the trans-anionic geometry in related RuX2LL′(═CHPh) species.

Hyperbranched Azo-Polymers Synthesized by Acyclic Diene Metathesis Polymerization of an AB2 Monomer

A novel hyperbranched azo-polymer was prepared by a ruthenium-based catalyst RuCl2(PCy3)(SIMes)(CHPh) using acyclic diene metathesis (ADMET) polymerization of an AB2 monomer, 4-undecylenyloxycarbonyl-4′-[bis(2-ethyl acrylate)amino]azobenzene, which was synthesized from the esterification reaction between N,N-bis(2-ethyl acrylate)aniline and 4-carboxy-4′-[bis(2-ethyl acrylate)amino]azobenzene. The monomer and polymer were characterized by mass spectrometer, elemental analysis, IR, UV−vis, and NMR measurements. The produced polymers have molecular weights within 5.83 and 23.5 kDa, and their polydispersity indices range from 1.73 to 1.86 by multiangle laser light scattering-gel permeation chromatography (MALLS−GPC). The hyperbranched azo-polymer underwent efficient photoisomerization from trans to cis as observation in UV−vis spectroscopy. The degree of branching (DB) was determined by using 1H NMR spectroscopy and the values ranged from 0.57 to 0.45.

Ruthenium‐incorporated, metathesis‐active polyacetylene

AbstractTwo olefin metathesis methods have been developed for the preparation of metal‐incorporated polyacetylene (MIPA) with high levels of covalently attached ruthenium complex. Treatment of freshly prepared, porous polyacetylene (PA) formed by polymerization of acetylene by the metathesis catalyst (H2IMes)RuCl2(CHPh)(3‐bromopyridine)2 (G2B) with additional G2B resulted in the incorporation of the ruthenium complex into the solid polymer in levels up to 75% by mass, giving two‐step MIPA (MIPA2). Alternatively, single‐step MIPA (MIPA1) samples with similar levels (up to 79% by mass) of ruthenium incorporation were obtained by polymerization of acetylene with highly concentrated solutions of G2B, and the resulting materials formed fine suspensions in CH2Cl2. A variety of experiments confirmed that both the methods give materials with ruthenium covalently attached to PA chains. Shiny, tough MIPA films were obtained by pressing the black powders obtained by either method. Some MIPA properties were dependent on the amount of metal incorporation, but even samples with high incorporation levels mimicked untreated PA in many respects. MIPA1, but not MIPA2, was made electrically conductive by doping with iodine. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1061–1072, 2009

Synthesis of enantiopure 3,6,7,8-tetrahydrochromeno[7,8- d]imidazoles via asymmetric ketone hydrogenation in the presence of RuCl 2[Xyl-P-Phos][DAIPEN

The asymmetric hydrogenation of complex heterocyclic ketones 1 in the presence of the novel catalyst RuCl 2[( S)-Xyl-P-Phos][( S)-DAIPEN] and a base afforded the corresponding alcohols 2 in good enantiomeric purity. The outcome of the reaction depended on the substitution pattern of the ketone and the stoichiometry of the base. After optimization of the reaction conditions, the pure alcohols 2a and 2b were isolated in good yield (>70%) and enantiomeric purity (>93% ee) and used as key intermediates for the synthesis of the pharmaceutically active 3,6,7,8-tetrahydrochromeno[7,8- d]imidazoles 3a and 3b.

Preparation of tricyclic imidazopyridines by asymmetric ketone hydrogenation in the presence of ruthenium phosphino-oxazoline catalyst

The asymmetric hydrogenation of the prochiral heterocyclic ketone 2 and its O-protected analogues 9 to 11 in the presence of the ruthenium POX catalyst RuCl 2(PPh 3)(Ph 2P-Fc-oxa i Pr) was studied. The reactivity of the substrate and the enantioselectivity of the reduction depended on the nature of the protecting group. The best results were achieved with the thexyldimethylsilyl protecting group: the corresponding alcohol 13 was obtained in 86% yield and 88% ee and constitutes a valuable intermediate for the synthesis of the potassium-competitive acid blocker BYK 311319 1.

Ring‐opening metathesis polymerization of functionalized cyclooctene by a ruthenium‐based catalyst in ionic liquid

AbstractThis paper describes the synthesis of a novel monomer of 5‐substituted cyclooctene with the pendant of imidazolium salt (7) and the ring‐opening metathesis polymerization of the functionalized cyclooctenes (4 and 7) in CH2Cl2 and ionic liquid [bmim][PF6] by a ruthenium‐based catalyst RuCl2(PCy3)(SIMes)(CHPh) (2). The polymerization, which was carried out in ionic liquid, afforded improved control over the molecular weight (Mn) and polydispersity of the resultant products (PDI <1.4). Furthermore, to facilitate the GPC measurement for molecular weight of polymers, the charged polymers (poly‐7) were hydrolyzed to give uncharged polymers (poly‐4*) by removing the imidazolium pendant from the polymer chains. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3986–3993, 2007

The controlled homogeneous organic solution polymerization of new hydrophilic cationic exo‐7‐oxanorbornenes via ROMP with RuCl2(PCy3)2CHPh in a novel 2,2,2‐trifluoroethanol/methylenechloride solvent mixture

AbstractThe authors detail herein the synthesis and controlled polymerization of a series of new permanently cationic ammonium exo‐7‐oxanorbornene derivatives via ROMP, with the first generation Grubbs' catalyst RuCl2(PCy3)2CHPh, in a novel solvent mixture composed of 1:1 vol/vol 2,2,2‐trifluoroethanol (TFE)/methylene chloride. It is demonstrated that this cosolvent mixture is a convenient reaction medium facilitating the polymerization of hydrophilic substrates by hydrophobic initiators under homogeneous conditions. Homopolymerizations and copolymerizations proceed yielding materials with controlled molecular masses, and narrow molecular mass distributions. It is also demonstrated that this protocol is not limited to the use of TFE as a cosolvent and that additional halogenated alcohols, such as 2,2,2‐trichloroethanol and 1,1,1,3,3,3‐hexafluoroisopropanol are also effective cosolvents for the controlled polymerization of such cationic substrates. Finally, it is demonstrated that the TFE/methylene chloride mixture has no apparent detrimental effect on Grubbs' catalyst. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2113–2128, 2007

A new route to Vitamin E key-intermediates by olefin cross-metathesis

The ruthenium-catalyzed olefin cross-metathesis has been successfully applied to the synthesis of derivatives of phytyltrimethylhydroquinone. These products, containing a trisubstituted olefinic double bond, are useful intermediates for an alternative route to α-tocopheryl acetate (Vitamin E acetate). Using the second generation Grubbs’ catalyst RuCl 2(C 21H 26N 2)(CHPh)PCy 3 (Cy = cyclohexyl) and Hoveyda–Grubbs’ catalyst RuCl 2(C 21H 26N 2){CH-C 6H 4(O-iPr)-2}, the reactions were performed with various C-allylated and O-allylated derivatives of trimethylhydroquinone-1-acetate as substrates. 2,6,10,14-Tetramethylpentadec-1-ene and derivatives of phytol were employed as olefin partners for the cross-metathesis reactions. The Vitamin E precursors could be prepared in up to 83% isolated yields as mixtures of E and Z stereoisomers.

A New Route to Vitamin E Key‐Intermediates by Olefin Cross‐Metathesis

AbstractRu‐Catalyzed olefin cross‐metathesis (CM) has been successfully applied to the synthesis of several phytyl derivatives (2b, 2d–f, 3b) with a trisubstituted CC bond, as useful intermediates for an alternative route to α‐tocopheryl acetate (vitamin E acetate; 1b) (Scheme 1). Using the second‐generation Grubbs catalyst RuCl2(C21H26N2)(CHPh)PCy3 (Cy = cyclohexyl; 4a) and Hoveyda–Grubbs catalyst RuCl2(C21H26N2){CH‐C6H4(O‐iPr)‐2} (4b), the reactions were performed with various C‐allyl (5a–f, 7a,b) and O‐allyl (8a–d) derivatives of trimethylhydroquinone‐1‐acetate as substrates. 2,6,10,14‐Tetramethylpentadec‐1‐ene (6a) and derivatives 6c–e of phytol (6b) as well as phytal (6f) were employed as olefin partners for the CM reactions (Schemes 2 and 5). The vitamin E precursors could be prepared in up to 83% isolated yield as (E/Z)‐mixtures.

New pseudohalide ligands in Ru-catalyzed olefin metathesis — A robust, air-activated iminopyrrolato catalyst

Reaction of the Grubbs catalyst RuCl2(PCy3)2(CHPh) (1) with lithium 2-[(2,6-diisopropylphenyl)imino]pyrrolide·Et2O (LiNN′·Et2O) gives alkylidene complex 5, containing a chelating, σ-bound iminopyrrolato unit. The structure of 5 is confirmed by X-ray crystallography. Treatment of 5 with pyridine generates RuCl(NN′)(py)2(CHPh) (6) via displacement of PCy3. Complex 5 effects ring-closing metathesis in air, displaying high reactivity relative to 6.Key words: ruthenium, alkylidene, metathesis, pyrrolimine, iminopyrrolato.