Showing papers on "Metathesis published in 2000"
TL;DR: In this article, the crystal structure of Ru complex 5, bearing a 1,3dimesityl-4,5-dihydroimidazol-2-ylidene and styrenyl ether ligand is disclosed.
Abstract: Several highly active, recoverable and recyclable Ru-based metathesis catalysts are presented. The crystal structure of Ru complex 5, bearing a 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene and styrenyl ether ligand is disclosed. The heterocyclic ligand significantly enhances the catalytic activity, and the styrenyl ether allows for the easy recovery of the Ru complex. Catalyst 5 promotes ring-closing metathesis (RCM) and the efficient formation of various trisubstituted olefins at ambient temperature in high yield within 2 h; the catalyst is obtained in >95% yield after silica gel chromatography and can be used directly in subsequent reactions. Tetrasubstituted olefins can also be synthesized by RCM reactions catalyzed by 5. In addition, the synthesis and catalytic activities of two dendritic and recyclable Ru-based complexes are disclosed (32 and 33). Examples involving catalytic ring-closing, ring-opening, and cross metatheses are presented where, unlike monomer 5, dendritic 33 can be readily recovered.
1,748 citations
TL;DR: In this paper, the authors provide an overview of the development of catalysts for olefin metathesis which combine high activity, durability, and excellent tolerance towards polar functional groups.
Abstract: The advent of well-defined catalysts for olefin metathesis which combine high activity, durability, and excellent tolerance towards polar functional groups has revolutionized the field. The past decade has seen the rapid embrace of these reagents as tools for advanced organic and polymer chemistry and the success of this development is witnessed by a plethora of elegant applications to the synthesis of natural and nonnatural products. This review article provides an overview of these developments and intends to familiarize the reader with some very recent advances which hold the promise to expand the scope of the reaction even further. Moreover, the positive impact of metathesis on the fundamental logic of retrosynthetic planning is demonstrated by means of typical examples. Finally, it will be shown that metathesis is by no means restricted to alkenes as substrates, and some comments on metathesis reactions following unconventional mechanistic pathways will also be presented.
1,614 citations
703 citations
567 citations
TL;DR: In this paper, a single-step synthesis of α-functionalized olefins by intermolecular cross-metathesis and intramolecular ring-closing metathesis using ruthenium alkylidene 3 was reported.
Abstract: The generation of olefins with electron-withdrawing functionality, such as α,β-unsaturated aldehydes, ketones, and esters, remains a difficult task in organic chemistry. A practical method to approach this problem would involve olefin metathesis, utilizing well-defined alkylidenes such as ((CF_3)_2MeCO)_2(ArN)Mo CH(t-Bu) (1) and (Pcy_3)_2Cl_2Ru CHPh (2). However, the generation of olefins with vinylic functionality through the use of cross-metathesis (CM) has met with limited success. In one of the few reports of this reaction, Crowe and Goldberg demonstrated that acrylonitrile participated in cross-metathesis reactions with a variety of terminal olefins. Other π-conjugated olefins, such as enones and enoic esters, were not functional group compatible with alkylidene 1 and failed to react with 2 in cross-metathesis. Recently, the highly active ruthenium-based olefin metathesis catalyst 3, which contains a 1,3-dimesityl-4,5-dihydro-imidazol-2-ylidene ligand, was found to efficiently catalyze the cross-metathesis of 1,1-geminally disubstituted olefins.7 Because ruthenium alkylidene 3 displayed unique activity toward previously metathesis-inactive substrates, we decided to investigate the metathesis of α-functionalized olefins. In this communication, we report the single-step synthesis of α-functionalized olefins by intermolecular cross-metathesis and intramolecular ring-closing metathesis using ruthenium alkylidene 3.
546 citations
519 citations
TL;DR: In this article, synthesis and activity in ring closure metathesis (RCM) and cross-metathesis of the phosphine-free 1,3-dimesityl-4,5-dihydroimidazole-2-ylidene (IHMes) ruthenium alkoxybenzylide complex 6 are reported.
467 citations
428 citations
TL;DR: The ruthenium carbene complexes 3a,b bearing imidazol-2-ylidene ligands constitute excellent precatalysts for ring-closing metathesis (RCM) reactions allowing the formation of tri- and tetrasubstituted cycloalkenes and their reactivity was found to be highly dependent on the reaction medium.
Abstract: The ruthenium carbene complexes 3a,b bearing imidazol-2-ylidene ligands constitute excellent precatalysts for ring-closing metathesis (RCM) reactions allowing the formation of tri- and tetrasubstituted cycloalkenes. They also apply to annulations that are beyond the scope of the standard Grubbs carbene 1 as well as to ring-closing reactions of acrylic acid derivatives even if the resulting α,β-unsaturated lactones (or lactams) are tri- or tetrasubstituted. The reactivity of 3a was found to be highly dependent on the reaction medium: particularly high reaction rates are observed in toluene, although this solvent also leads to an increased tendency of the catalyst to isomerize the double bonds of the substrates.
392 citations
TL;DR: In this paper, a new methodology for the selective cross-metathesis (CM) of terminal olefins employing ruthenium benzylidene 1 was described, and the results demonstrated distinct advantages in reaction rate and stereoselectivity for reactions employing the disubstituted olefs.
Abstract: New methodology for the selective cross-metathesis (CM) of terminal olefins employing ruthenium benzylidene 1 is described.1 CM with symmetric internal olefins was found to provide a useful means for homologating terminal olefins to protected allylic alcohols, amines, and esters. Due to the limited commercial availability of symmetric internal olefins, a two-step CM procedure was developed in which terminal olefins were first homodimerized prior to the CM reaction. Terminal olefins with allylic methyl substituents were observed to provide CM products in diminished yield albeit with markedly improved trans-selectivity. Reaction rates were measured for CM reactions utilizing butenediol and allyl alcohol derivatives, and the results demonstrated distinct advantages in reaction rate and stereoselectivity for reactions employing the disubstituted olefins. In the course of studies of substrates with allylic oxygen substituents, a new CM application was discovered involving the metathesis of acrolein acetal derivatives with terminal olefins. Acrolein acetals, including asymmetric variants derived from tartaric acid, proved to be exceptionally robust and trans-selective CM substrates. In related work, a pinacol-derived vinyl boronate was also found to be a reactive CM partner, providing a novel means for converting terminal olefins into precursors for the Suzuki coupling reaction.
356 citations
TL;DR: A series of well accessible cationic ruthenium allenylidene complexes of the general type [(eta6-arene)(R3P)RuCl(=C=CR'2)]+ X- is described, which constitute a new class of pre-catalysts for ring closing olefin metathesis reactions (RCM) and provide an unprecedented example for the involvement of metal allanylidenes in catalysis.
Abstract: A series of well accessible cationic ruthenium allenylidene complexes of the general type [(eta6-arene)(R3P)RuCl(=C=CR'2)]+ X- is described which constitute a new class of pre-catalysts for ring closing olefin metathesis reactions (RCM) and provide an unprecedented example for the involvement of metal allenylidenes in catalysis. They effect the cyclization of various functionalized dienes and enynes with good to excellent yields and show a great tolerance towards an array of functional groups. Systematic variations of their basic structural motif have provided insights into the essential parameters responsible for catalytic activity which can be enhanced further by addition of Lewis or Bronsted acids, by irradiation with UV light, or by the adequate choice of the "non-coordinating" counterion X-. The latter turned out to play a particularly important role in determining the rate and selectivity of the reaction. A similarly pronounced influence is exerted by remote substituents on the allenylidene residue which indicates that this ligand (or a ligand derived thereof) may remain attached to the metal throughout the catalytic process. X-ray crystal structures of the catalytically active allenylidene complexes 3b.PF6 and 15.OTf as well as of the chelate complex 10 required for the preparation of the latter catalyst are reported.
TL;DR: The first C-C single-bond metathesis in homogeneous solution was discovered and remarkable structures and reactions including five-membered metallacyclocumulenes were discovered.
Abstract: A thorough investigation of the reactions of diynes, R(C⋮C)2R, and polyynes, R(C⋮C)nR, with titanocene and zirconocene was performed using the metallocene sources Cp2M(L)(η2-Me3SiC⋮CSiMe3) (M = Ti, L = −; M = Zr, L = THF, pyridine). The conversions show an array of different products generated in complexation, coupling, and cleavage reactions. These results include remarkable structures (e.g., five-membered metallacyclocumulenes) and reactions (e.g., C−C single-bond cleavage). In addition, the first C−C single-bond metathesis in homogeneous solution was discovered. The presented findings have been supported by theoretical studies.
TL;DR: The olefin metathesis reaction of the Grubbs ruthenium carbene complexes has been investigated in the gas phase by electrospray ionization tandem mass spectrometry as mentioned in this paper.
Abstract: The olefin metathesis reaction of the Grubbs ruthenium carbene complexes has been investigated in the gas phase by electrospray ionization tandem mass spectrometry. Relative rates of reaction for substituted ruthenium benzylidenes and alkylidenes after removal of one phosphine ligand were interpreted with the aid of linear free energy analysis and kinetic isotope effects. The experimental observations are consistent with a reaction profile in which the metallacyclobutane structure is a transition state rather than an intermediate, although alternative explanations cannot be wholly ruled out. Electron withdrawal on the carbene moiety is found to accelerate the metathesis reaction when only the metathesis step itself is examined. Quantum chemical calculations at a variety of levels were performed to check for the consistency of the interpretation.
TL;DR: Ruthenium alkylidenes 6 and 7 bearing cationically functionalized phosphine ligands are soluble and stable in protic solvents and initiate olefin metathesis reactions in methanol, water, and aqueous emulsions as mentioned in this paper.
Abstract: Ruthenium alkylidenes 6 and 7 bearing cationically functionalized phosphine ligands are soluble and stable in protic solvents and initiate olefin metathesis reactions in methanol, water, and aqueous emulsions. NMR spectroscopy data and X-ray diffraction analyses of alkylidene 6 suggested that these new alkylidenes were structurally similar to previously reported complexes of the type (PR3)2Cl2RuCHR, in which the alkylidene substituents lie in the Cl−Ru−Cl plane. The anionic chloride ligands of complexes 6 and 7 were found to undergo facile ligand exchange reactions with other anions in protic solution. Both alkylidenes initiate the ring-opening metathesis polymerization (ROMP) of strained, cyclic olefins in water. However, the propagating species in these reactions decompose prior to complete consumption of monomer. These complexes initiate the quantitative, living polymerization of functionalized monomers in water in the presence of a Bronsted acid. Both chain termination and chain transfer reactions wer...
TL;DR: In this paper, a ring-opening metathesis copolymerization of norborn-2-ene (NBE) and 1,4,4a,5,8,8a-hexahydro (DMN-H6) within borosilicate columns in the presence of porogenic solvents such as toluene, methylene chloride, methanol, and 2-propanol were used throughout.
Abstract: Functionalized monolithic materials have been prepared by ring-opening metathesis copolymerization of norborn-2-ene (NBE) and 1,4,4a,5,8,8a-hexahydro-1,4,5,8-exo,endo-dimethanonaphthalene (DMN-H6) within borosilicate columns in the presence of porogenic solvents such as toluene, methylene chloride, methanol, and 2-propanol. Grubbs-type initiators of the general formula Cl2(PR3)2Ru(CHPh) (R = phenyl, cyclohexyl) were used throughout. The resulting separation media possess microstructures consisting of microporous, spherical microglobules with a narrow microglobule size distribution. By variation of the polymerization conditions in terms of stoichiometry of the monomers, porogenic solvents, and temperature, microglobule diameters may be varied within a range of 2 ± 1 μm up to 30 ± 10 μm. Specific surface areas (σ) and inter-microglobule pore volumes (ez) may be altered within 60−210 m2/g and 2−50%, respectively. Nonfunctionalized separation media were successfully used for the separation of 10 different mod...
TL;DR: The potential use of olefin metathesis reactions in carbohydrate chemistry is discussed in this article, where the use of OO reactions for the construction of carbon--carbon bonds has been significantly expanded with the development of efficient and well-defined============catalytic systems.
TL;DR: A series of norbornene-based, l-valine-and l-phenylalanine-containing chiral monomers have been synthesized in this article, starting from norborn-2-ene-5-carboxylic acid chloride and norborn 2-ene5,6-dicarboxyric anhydride.
Abstract: A series of norbornene-based, l-valine- and l-phenylalanine-containing chiral monomers have been prepared. Starting from norborn-2-ene-5-carboxylic acid chloride and norborn-2-ene-5,6-dicarboxylic anhydride, N-(norborn-2-ene-5-carboxyl)-l-valine (I), N-(norborn-2-ene-5-carboxyl)-l-phenylalanine (II), N-(norborn-2-ene-5-carboxyl)-l-phenylalanine ethyl ester (III), the N,N-(norborn-2-ene-5,6-dicarbimid) (NBDCI)-protected amino acid derivatives NBDCI-l-valine (IV), NBDCI-l-phenylalanine (V), NBDCI-l-valine-tert-butylamide (VI), NBDCI-l-valine-anilide (VII), NBDCI-l-valine-m-nitroanilide (VIII), and NBDCI-l-valine-p-chloroanilide (IX) have been synthesized. Compounds I−IX were polymerized via ring-opening metathesis polymerization (ROMP) using initiators based on both molybdenum (Mo(N-2,6-Me2-C6H3)(CHCMe2Ph)(OCMe(CF3)2)2) (1) and ruthenium (Cl2Ru(CHPh-p-F)(PCy3)2, Cy = cyclohexyl) (2). The polymers were characterized in terms of cis/trans structure as well as optical rotation. Bromomethylated, beaded polymer ...
TL;DR: The synthesis of 1 via RCM is compared with an alternative approach employing a low-valent titanium-induced McMurry coupling of dialdehyde 47 for the formation of the large ring and this direct comparison clearly ends in favor of metathesis which turned out to be superior in all preparatively relevant respects.
Abstract: Total syntheses of the bioactive orsellinic acid derivatives zearalenone 3 and lasiodiplodin 1 are reported based on a ring-closing metathesis (RCM) reaction of styrene precursors as the key steps. These and closely related macrocyclizations are catalyzed with high efficiency by the “second generation” ruthenium carbene catalyst 5 bearing a N-heterocyclic carbene ligand, whereas the standard Grubbs carbene 4 fails to afford any cyclized product. Only the (E)-isomer of the macrocyclic cycloalkene is formed in all cases. The substrates for RCM can be obtained either via a Stille cross-coupling reaction of tributylvinylstannane or, even more efficiently, by Heck reactions of the aryl triflate precursors with pressurized ethene. Furthermore, the synthesis of 1 via RCM is compared with an alternative approach employing a low-valent titanium-induced McMurry coupling of dialdehyde 47 for the formation of the large ring. This direct comparison clearly ends in favor of metathesis which turned out to be superior in...
TL;DR: A newly reported metathesis catalyst was show to be highly effective for cyclization of halichlorine and pinnaic acid model systems.
TL;DR: Transition metal-catalyzed imine metathesis reactions that are mechanistically analogous to olefin metatheses reactions catalyzed by metal carbene complexes are developed and characteristic selectivity appears to be unique to the zirconium-mediated system.
Abstract: By kinetically stabilizing imidozirconocene complexes through the use of a sterically demanding ligand, or by generating a more thermodynamically stable resting state with addition of diphenylacetylene, we have developed transition metal-catalyzed imine metathesis reactions that are mechanistically analogous to olefin metathesis reactions catalyzed by metal carbene complexes. When 5 mol % of Cp*Cp(THF)ZrNtBu is used as the catalyst precursor in the metathesis reaction between PhCHNPh and p-TolCHN-p-Tol, a 1:1:1:1 equilibrium mixture with the two mixed imines p-TolCHNPh and PhCHN-p-Tol is generated in C6D6 at 105 °C. The catalyst was still active after 20 days with an estimated 847 turnovers (t1/2 170 m; TON = 1.77 h-1). When the azametallacyclobutene Cp2Zr(N(Tol)C(Ph)C(Ph)) is used as the catalyst precursor under similar reaction conditions, a total of 410 turnovers are obtained after 4 days (t1/2 170 m; TON = 4.3 h-1). An extensive kinetic and equilibrium analysis of the metallacyclobutene-catalyzed meta...
Patent•
22 May 2000TL;DR: In this article, a novel metathesis catalysts with an imidazolidine-based ligand and methods for making and using the same are described. But the present method is limited to the use of a single atom.
Abstract: The present invention relates to novel metathesis catalysts with an imidazolidine-based ligand and to methods for making and using the same. The inventive catalysts are of formula (I) wherein : M is ruthemium or osmium; X and X1 are each independently an anionic ligand; L is a neutral electron donor ligand; and, R, R?1, R6, R7, R8 and R9? are each independently hydrogen or a substituent selected from the group consisting of C?1?-C20 alkyl, C2-C20 alkenyl, C2-C20 alkynyl, aryl, C1-C20 carboxylate, C1-C20 alkoxy, C2-C20 alkenyloxy, C2-C20 alkynyloxy, aryloxy, C2-C20 alkoxycarbonyl, C1-C20 alkylthiol, aryl thiol, C1-C20 alkylsulfonyl and C1-C20 alkylsulfinyl, the substituent optionally substituted with one or more moieties selected from the group consisting of C1-C10 alkyl, C1-C10 alkoxy, aryl, and a functional group selected from the group consisting of hydroxyl, thiol thioether, ketone, aldehyde, ester, ether, amine, imine, amide, nitro, carboxylic acid, disulfide, carbonate, isocyanate, carbodiimide, carboalkoxy, carbamate, and halogen. The inclusion of an imidazolidine ligand to the previously described ruthenium or osmium catalysts has been found to dramatically improve the properties of theses complexes. The inventive catalysts maintains the functional group tolerance of previously described ruthenium complexes while having enhanced metathesis activity that compares favorably to prior art tungsten and molybdenum systems.
TL;DR: In this article, the authors showed that CO2 insertion into the Ru−H bond occurs with an activation energy (Ea) of 29.3 kcal/mol in cis-RuH2(PH3)4 and with an Ea value of 10.3 kg/m 2 in six-membered σ-bond metathesis of RuH(η1-OCOH)3(H2).
Abstract: Ruthenium-catalyzed hydrogenation of CO2 into formic acid was theoretically investigated with the DFT(B3LYP) method, where cis-RuH2(PH3)4 was adopted as a catalyst model. Theoretical calculations show that (1) CO2 insertion into the Ru−H bond occurs with an activation energy (Ea) of 29.3 kcal/mol in cis-RuH2(PH3)4 and with an Ea value of 10.3 kcal/mol in cis-RuH2(PH3)3; (2) six-membered σ-bond metathesis of RuH(η1-OCOH)(PH3)3(H2) occurs with a much smaller Ea value (8.2 kcal/mol) than four-membered σ-bond metathesis (Ea = 24.8 kcal/mol) and five-membered H−OCOH reductive elimination (Ea = 25.5 kcal/mol); (3) three-membered H−OCOH reductive elimination requires a very much larger Ea value of 43.2 kcal/mol; (4) if PH3 dissociates from cis-RuH2(PH3)4, the CO2 hydrogenation takes place through the CO2 insertion into the Ru−H bond of RuH2(PH3)3 followed by the six-membered σ-bond metathesis, where the rate-determining step is the CO2 insertion; and (5) if PH3 does not dissociate from cis-RuH2(PH3)4 and cis-RuH...
TL;DR: In this paper, the synthesis of conjugated polymers by acyclic diyne metathesis (ADIMET) was reported, where simple in situ catalysts formed from Mo(CO)6 and 4-chlorophenol were used to metathesize the dipropynyl(tetraalkyl)stilbene monomers.
Abstract: The synthesis of novel conjugated polymers by acyclic diyne metathesis (ADIMET) is reported. These polymers are hybrids between poly(p-phenylenevinylene) and poly(p-phenyleneneethynylene) (PPE). They contain phenylene, ethynylene, and vinylene groups (⋮PhPh, PPVE). Simple in situ catalysts formed from Mo(CO)6 and 4-chlorophenol were used to metathesize the dipropynyl(tetraalkyl)stilbene monomers. The monomers are made by a combination of Horner reactions and Heck-type couplings. The PPVEs form in high yields and are structurally defined. They show degrees of polymerization (Pn) of 30−220 repeating units (i.e. 60−450 benzene rings), demonstrating that the presence of the double bonds does not interfere with alkyne metathesis. The PPVEs were structurally characterized by XRD and electron microscopy. They show fibrillar and network-type morphologies, which should make them interesting for applications in molecular electronics. Solid samples of PPVEs display powder XRD patterns almost identical to those of th...
TL;DR: These novel approaches are distinguished by the ready accessibility of the required cyclopentenone substrates via a three-component coupling reaction, the inherent flexibility which allows one to make a series of analogues starting from these common platforms, a small number of steps, and an excellent overall yield.
Abstract: The suitably functionalized cyclopentanone derivatives 12, 13, 19, and 37 serve as common precursors for the synthesis of various prostaglandins, prostaglandin-1,15-lactones, and unnatural analogues thereof. All of them contain a 2-butynyl entity which is elaborated into the intact α side chain of the targets either via a sequence comprising ring closing alkyne metathesis/Lindlar reduction or via alkyne cross metathesis (ACM)/Lindlar reduction. These novel approaches are distinguished by (i) the ready accessibility of the required cyclopentenone substrates via a three-component coupling reaction, (ii) the inherent flexibility which allows one to make a series of analogues starting from these common platforms, (iii) a small number of steps, and (iv) an excellent overall yield. The key alkyne metathesis reactions are efficiently catalyzed either by the tungsten alkylidyne complex (t-BuO)3W⋮CCMe3 or, preferentially, by a catalyst formed in situ from Mo[N(t-Bu)(Ar)]3 and CH2Cl2, the reactivity of which can be...