Grubbs-Hoveyda Type Research Articles

λ−carrageenan based ammonium-tagged Hoveyda-Grubbs type catalyst: Novel heterogeneous system for olefin metathesis

An ammonium tagged Hoveyda-Grubbs-type catalyst, i.e., FixCat, was non-covalently heterogenized for the first time in a λ−carrageenan xerogel via ion-exchange, which was confirmed by FTIR, SEM-EDS and TGA analyses. The new heterogeneous catalyst, i.e., λ−FixCat, was successfully employed in ring-closing metathesis using representative olefins in several solvents without leaching of the complex. The best catalytic performances were detected in the nonpolar solvents hexane and toluene. The activity of λ−FixCat was shown to be superior in toluene in terms of catalyst reusability, as it was easily separated from the reaction mixture, and it was successfully recycled five times. This study is part of our ongoing efforts to demonstrate the applicability of natural polysaccharides as supports for various catalysts.

Electrophilicity of Hoveyda-Grubbs Olefin Metathesis Catalysts as the Driving Force that Controls Initiation Rates.

The dissociative mechanism of initiation for a series of Hoveyda-Grubbs type metathesis catalysts modified at the para and meta positions in the isopropoxybenzylidene ligand is investigated by means of DFT calculations. The electron donating/withdrawing capacity of the ligand was screened through the incorporation of various substituents such as halogens, nitro, alkoxides, ketones, esters, amines, and amides. Variations in structural parameters, energy barriers for the Ru-O bond dissociation, and Ru-O bond strength were examined as a function of the Hammett constant. It was found that electronic properties of the catalysts such as chemical potential, hardness, and electrophilicity correlate linearly with the dissociative energy barriers. These findings enable a systematic rationalization and prediction of rate of precatalyst initiation through the calculation of only the HOMO-LUMO gap of catalysts, as the faster the initiation, the more electrophilic the catalyst.

Self-Supported Polymeric Ruthenium Complexes as Olefin Metathesis Catalysts in Synthesis of Heterocyclic Compounds

New ruthenium olefin metathesis catalysts containing N-heterocyclic carbene (NHC) connected by a linker tether to a benzylidene ligand were studied. Such obtained self-chelated Hoveyda–Grubbs type complexes existed in the form of an organometallic polymer but could still catalyze olefin metathesis after being dissolved in an organic solvent. Although these polymeric catalysts exhibited a slightly lower activity compared to structurally related nonpolymeric catalysts, they were successfully used in a number of ring-closing metathesis reactions leading to a variety of heterocyclic compounds, including biologically and pharmacologically related analogues of cathepsin K inhibitor and sildenafil (Viagra™). In the last case, a good solubility of a polymeric catalyst in toluene allowed the separation of the product from the catalyst via simple filtration.

Synthesis and Catalytic Properties of a Very Latent Selenium-Chelated Ruthenium Benzylidene Olefin Metathesis Catalyst.

Herein, we describe a study of the synthesis, characterization, and catalytic properties of a cis-dichlorido seleno-chelated Hoveyda–Grubbs type complex (Ru8). Such a complex has been obtained through a straightforward and high-yielding synthetic protocol in three steps from the commercially available 2-bromobenzaldehyde in good overall yield (54%). The catalytic profile, especially the latency of this complex, has been probed through selected olefin metathesis reactions such as ring-closing metathesis (RCM), self-cross-metathesis (self-CM) and ring-opening metathesis polymerization (ROMP). In addition to its high latency, the selenium Hoveyda-type complex Ru8 exhibits a switchable behavior upon thermal activation. Of interest, while the corresponding sulfur-chelated Hoveyda type catalyst is reported to be only activated by heat, the selenium analogue was found to be active upon both heat and light irradiation.

The Influence of Various N-Heterocyclic Carbene Ligands on Activity of Nitro-Activated Olefin Metathesis Catalysts.

A set of nitro-activated ruthenium-based Hoveyda-Grubbs type olefin metathesis catalysts bearing sterically modified N-hetero-cyclic carbene (NHC) ligands have been obtained, characterised and studied in a set of model metathesis reactions. It was found that catalysts bearing standard SIMes and SIPr ligands (4a and 4b) gave the best results in metathesis of substrates with more accessible C–C double bonds. At the same time, catalysts bearing engineered naphthyl-substituted NHC ligands (4d–e) exhibited high activity towards formation of tetrasubstituted C–C double bonds, the reaction which was traditionally Achilles’ heel of the nitro-activated Hoveyda–Grubbs catalyst.

Functionalization of (-)-β-pinene and (-)-limonene via cross metathesis with symmetrical internal olefins

The straightforward functionalization of sterically demanding α,α-disubstituted double bonds of the natural products β-pinene and limonene via cross metathesis with symmetrical internal olefins is described. The reaction is catalyzed by Hoveyda-Grubbs type ruthenium catalysts in dimethyl carbonate as green solvent and makes possible the clean introduction of ester and nitrile groups in one step without formation of byproducts.

The Development of a Method for the Production of Structural Polymeric Materials on the Basis of Norbornene Derivatives

Process parameters of the polymerization of a mixture of exo,exo- and endo,endo-dimethyl esters of norbornene-2,3-dicarboxylic acid in the bulk of the monomer under the action of a ruthenium catalyst of the Hoveyda–Grubbs type are developed. The effect of the concentration of the catalyst on the physical and mechanical properties of poly(norbornene-2,3-dicarboxylic acid dimethyl ester) is studied.

Unexpected formation of nitroso-chelated cyclic η1-acylruthenium(II) complex, an effective catalysts for transfer hydrogenation reaction

Reaction of commercial ruthenium complexes M31 and M20 with 2-nitrostyrene gave a new nitroso-chelated cyclic η1-acyl ruthenium(II) complexes Ru-4 and Ru-6 respectively instead of expected Hoveyda-Grubbs type (pre)catalyst Ru-3. New complexes were characterized by means of standard analytical techniques and their crystallographic structure has been confirmed by X-ray structural analysis. It was found that Ru-4 and Ru-6 do not exhibit any activity in standard metathesis reactions. However, a dramatic increase of activity was observed upon treatment with (trimethylsilyl)diazomethane, allowed for the successful application of Ru-4 in ROMP of endo,exo-bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic acid dimethyl ester. Moreover, such complexes can be effective catalysts of transfer hydrogenation of ketones as well as cycloisomerization reactions.

Metathesis of cardanol over ammonium tagged Hoveyda-Grubbs type catalyst supported on SBA-15

Cardanol (a mixture of phenols with C15 aliphatic unsaturated chain in meta position, manufactured from cashew nut shell liquids) is an abundant and till now practically waste natural material. An important way leading to its utilization as a renewable source of valuable phenolic compounds is represented by olefin metathesis.Quaternary ammonium tagged Ru complex of Hoveyda-Grubbs type immobilized on SBA-15 mesoporous molecular sieve by non-covalent interactions was proved as a very efficient catalyst for cardanol metathesis under mild conditions (35°C, toluene, 0.1 mol% of catalyst). The catalyst was used also in cross-metathesis of cardanol with alkenes (1-hexene, 1-heptene, 3-hexene, 4-octene) and unsaturated esters (methyl acrylate, 1,4-diacetoxybutene-2) under high yields of cross-metathesis products. The catalysts exhibited low leaching (from 0.2ppm to 2.9ppm Ru in products) and can be used in a continuous flow reactor (cumulative TON=2500).

ChemInform Abstract: Metatheases: Artificial Metalloproteins for Olefin Metathesis

AbstractReview: 45 refs.

Metatheases: artificial metalloproteins for olefin metathesis.

The incorporation of organometallic catalyst precursors in proteins results in so-called artificial metalloenzymes. The protein structure will control activity, selectivity and stability of the organometallic site in aqueous medium and allow non-natural reactions in biological settings. Grubbs-Hoveyda type ruthenium catalysts with an N-heterocyclic carbene (NHC) as ancillary ligand, known to be active in olefin metathesis, have recently been incorporated in various proteins. An overview of these artificial metalloproteins and their potential application in olefin metathesis is given.

Ru complexes of Hoveyda-Grubbs type immobilized on lamellar zeolites: activity in olefin metathesis reactions.

Hoveyda–Grubbs type catalysts with cationic tags on NHC ligands were linker-free immobilized on the surface of lamellar zeolitic supports (MCM-22, MCM-56, MCM-36) and on mesoporous molecular sieves SBA-15. The activity of prepared hybrid catalysts was tested in olefin metathesis reactions: the activity in ring-closing metathesis of citronellene and N,N-diallyltrifluoroacetamide decreased in the order of support MCM-22 ≈ MCM-56 > SBA-15 > MCM-36; the hybrid catalyst based on SBA-15 was found the most active in self-metathesis of methyl oleate. All catalysts were reusable and exhibited low Ru leaching (<1% of Ru content). XPS analysis revealed that during immobilization ion exchange between Hoveyda–Grubbs type catalyst and zeolitic support occurred in the case of Cl− counter anion; in contrast, PF6− counter anion underwent partial decomposition.

Long-Spaced Polyamides: Elucidating the Gap between Polyethylene Crystallinity and Hydrogen Bonding

Aliphatic polyamides with so far inaccessibly low amide contents were prepared by acyclic diene metathesis (ADMET) copolymerization of N-(undec-10-en-1-yl)undec-10-enamide (1) and undeca-1,10-diene (2) applying different Grubbs and Hoveyda–Grubbs type olefin metathesis catalyst precursors, followed by exhaustive postpolymerization hydrogenation to yield saturated copolymers. These polyamides, containing between 1.0 and ca. 50.5 amide groups per 1000 methylene units, fill the gap between polyamides from classical polymerization approaches, like polycondensation of diamines with diacids, and linear polyethylene. With reduced amide concentrations the melting points of polyamides converge toward polyethylene, passing through a distinct melting point minimum observed around 110 °C for polyamides with ca. 35 amide groups per 1000 methylene units. The minimum goes in hand with a change in the crystal structure related to the different ratios of intersegment interactions from hydrogen bonding and nonpolar van der...

Hybrid ruthenium ROMP catalysts based on an engineered variant of β-barrel protein FhuA ΔCVF(tev) : effect of spacer length.

A biohybrid ring-opening olefin metathesis polymerization catalyst based on the reengineered β-barrel protein FhuA ΔCVF(tev) was chemically modified with respect to the covalently anchored Grubbs-Hoveyda type catalyst. Shortening of the spacer (1,3-propanediyl to methylene) between the N-heterocyclic carbene ligand and the cysteine site 545 increased the ROMP activity toward a water-soluble 7-oxanorbornene derivative. The cis/trans ratio of the double bond in the polymer was influenced by the hybrid catalyst.

Ring-opening metathesis polymerization of vinylnorbornene and following polymer modifications

Ring-opening metathesis polymerization of vinylnorbornene with molybdenum (VI) complex or with Hoveyda-Grubbs type Ru alkylidene complex provided soluble polymers, poly (VNBE)s of Mn about 10 000, having vinyl pendant groups on cyclopentenylenevinylene main chains. Post-polymerization modification via cross-metathesis of pendant vinyl groups with cis-1,4-diacetoxybut-2-ene, 5-hexenyl acetate, allyl acetoacetate, and allyltrimethylsilane was accomplished. Functionalization of poly (VNBE) was also performed via ene-yne cross-metathesis of vinyl pendants with (4-fluorophenyl) acetylene and (2,4-difluorophenyl) acetylene.

Ruthenium Olefin Metathesis Catalysts with Frozen NHC Ligand Conformations

The catalytic behavior of Grubbs and Hoveyda–Grubbs II type ruthenium complexes bearing N-heterocyclic carbene (NHC) ligands with syn-phenyl groups on the backbone and syn- or anti-oriented o-tolyl N-substituents was evaluated in a series of olefin metathesis transformations. Further advance in the synthesis of the best-performing syn catalysts and a deeper investigation into the solution-state structure of the Hoveyda–Grubbs type II complex with anti N-tolyl groups by 2D-NMR and DFT studies are also reported. Of particular interest, syn complexes emerged among the best-performing catalysts in all of the explored metathesis reactions, especially in the ring-closing metathesis (RCM) of hindered olefins, allowing also for the difficult formation of macrocyclic trisubstituted alkenes. An important unexpected result was obtained in the RCM of linalool, where both syn and anti catalysts appeared to be involved in the dehydration reaction of the cyclization product (1-methylcylopent-2-en-1-ol). This process all...

Metathesis of cardanol over Ru catalysts supported on mesoporous molecular sieve SBA-15

The Hoveyda–Grubbs type Zhan catalysts (ZC) and Grubbs second generation catalyst (GII) were immobilized on SBA-15 mesoporous molecular sieve by non-covalent interactions and phosphine linkers, respectively. Both hybrid catalysts proved to be highly active and selective in cardanol metathesis and cardanol cross-metathesis with ethene and cis-1,4-diacetoxy-2-butene (DAB). GII/SBA-15 was less active than ZC/SBA-15, however, Ru leaching was significantly lower for GII/SBA-15 (0.5%) than for ZC/SBA-15 (2.5%). In ethenolysis of cardanol, 3-(non-8-enyl)phenol was isolated as a major product. In cross-metathesis with DAB 9-(3-hydroxyphenyl)non-2-enyl acetate and non-2-enyl acetate were formed with high selectivity. Easy catalyst–product separation and low Ru leaching provide the products (applicable as detergent precursors and fragrance and flavor agents) free from the catalyst residue.

Living Polymerization of Monomers Containing endo-Tricyclo[4.2.2.02,5]deca-3,9-diene Using Second Generation Grubbs and Hoveyda–Grubbs Catalysts: Approach to Synthesis of Well-Defined Star Polymers

Living ROMP of monomers containing endo-tricyclo[4.2.2.02,5]deca-3,9-diene (TD) moieties was successfully performed using thermally stable second generation Grubbs and Hoveyda–Grubbs catalysts. Even slow-initiating catalysts enabled the living polymerization to give polymers with a narrow polydispersity index and controlled molecular weight because the unique structure of the TD monomers resulted in much faster initiation and slower propagation than conventional norbornene monomers. Kinetic analyses confirmed that the ratio of initiation/propagation rate (ki/kp) of the TD monomers was 10 to 200 times larger than that of norbornene derivatives. To demonstrate the living nature of the ROMP, block copolymers were successfully prepared using second generation Hoveyda–Grubbs catalyst for the first time. In addition, three-arm star polymers were prepared by core-first approach using Hoveyda–Grubbs type three-arm initiator, owing to the living ROMP of TD monomers with this stable catalyst. Also, star diblock cop...

Effect of Added Salt on Ring-Closing Metathesis Catalyzed by a Water-Soluble Hoveyda–Grubbs Type Complex To Form N-Containing Heterocycles in Aqueous Media

The efficiency of ring-closing metathesis catalyzed by a Hoveyda–Grubbs type catalyst in water can be enhanced by addition of a chloride salt under neutral conditions. UV–vis spectroscopic study showed that a characteristic band of the catalyst around 380 nm remained over 16 h in the presence of KCl, whereas the band distinctly decreased in the absence of KCl. The disappearance of the band is ascribed to a displacement of a chloride ligand by a water molecule or a hydroxide anion. The spectral changes can be related to the metathesis activity. The experimental results indicate that avoidance of the chloride ligand loss is important to maintain the metathesis activity in water.

A Hybrid Ring‐Opening Metathesis Polymerization Catalyst Based on an Engineered Variant of the β‐Barrel Protein FhuA

A β-barrel protein hybrid catalyst was prepared by covalently anchoring a Grubbs-Hoveyda type olefin metathesis catalyst at a single accessible cysteine amino acid in the barrel interior of a variant of β-barrel transmembrane protein ferric hydroxamate uptake protein component A (FhuA). Activity of this hybrid catalyst type was demonstrated by ring-opening metathesis polymerization of a 7-oxanorbornene derivative in aqueous solution.