Showing papers on "Acyclic diene metathesis published in 2006"
TL;DR: One example that achieves selectivity with respect to the distribution of product molecular weights is reported, in which n-decane is the predominant high-molecular-weight product of the metathesis of two moles of n-hexane.
Abstract: With petroleum supplies dwindling, there is increasing interest in selective methods for transforming other carbon feedstocks into hydrocarbons suitable for transportation fuel. We report the development of highly productive, well-defined, tandem catalytic systems for the metathesis of n-alkanes. Each system comprises one molecular catalyst (a "pincer"-ligated iridium complex) that effects alkane dehydrogenation and olefin hydrogenation, plus a second catalyst (molecular or solid-phase) for olefin metathesis. The systems all show complete selectivity for linear (n-alkane) product. We report one example that achieves selectivity with respect to the distribution of product molecular weights, in which n-decane is the predominant high-molecular-weight product of the metathesis of two moles of n-hexane.
485 citations
TL;DR: A novel water-soluble ruthenium olefin metathesis catalyst supported by a poly(ethylene glycol) conjugated saturated 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene ligand shows improved activity in ring-opening meetingathesis polymerization, ring-closing metatheses, and cross-metathesis reactions in aqueous media.
Abstract: A novel water-soluble ruthenium olefin metathesis catalyst supported by a poly(ethylene glycol) conjugated saturated 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene ligand is reported. The catalyst displays improved activity in ring-opening metathesis polymerization, ring-closing metathesis, and cross-metathesis reactions in aqueous media.
289 citations
TL;DR: Mechanistic explanations for the large sodium iodide effect as well as possible mechanistic pathways leading to the observed products are discussed.
Abstract: The synthesis of olefin metathesis catalysts containing chiral, monodentate N-heterocyclic carbenes and their application to asymmetric ring-closing metathesis (ARCM) are reported. These catalysts retain the high levels of reactivity found in the related achiral variants (1a and 1b). Using the parent chiral catalysts 2a and 2b and derivatives that contain steric bulk in the meta positions of the N-bound aryl rings (catalysts 3−5), five- through seven-membered rings were formed in up to 92% ee. The addition of sodium iodide to catalysts 2a−4a (to form 2b−4b in situ) caused a dramatic increase in enantioselectivity for many substrates. Catalyst 5a, which gave high enantiomeric excesses for certain substrates without the addition of NaI, could be used in loadings of ≤1 mol %. Mechanistic explanations for the large sodium iodide effect as well as possible mechanistic pathways leading to the observed products are discussed.
217 citations
TL;DR: Structural investigations suggest that a fluorine-ruthenium interaction is responsible for this increased activity of new rut henium-based olefin metathesis catalysts, featuring fluorinated NHC ligands.
Abstract: The synthesis, structure, and performance of new ruthenium-based olefin metathesis catalysts, featuring fluorinated NHC ligands are presented. The introduction of halogen atoms into the N-heterocyclic carbene ligand profoundly alters the catalytic activity and can afford a more efficient catalyst. Structural investigations suggest that a fluorine−ruthenium interaction is responsible for this increased activity.
170 citations
122 citations
TL;DR: In this article, the synthesis and screening of catalytic activity of two ruthenium carbene complexes 9 and 10 bearing substituents in 2-isopropoxybenzylidene ligand is described.
Abstract: Synthesis and screening of catalytic activity of two novel ruthenium carbene complexes 9 and 10 bearing substituents in 2-isopropoxybenzylidene ligand is described. These precatalysts constitute excellent tools for RCM and enyne metathesis by combining high stability with a possibility of their on-demand activation by heat and Bronsted (9) or Lewis acids (10).
86 citations
TL;DR: Overall, the reaction sequence converts acyclic enynes into vinyl cyclopropanes in single operation through two unique ruthenium-catalyzed transformations.
Abstract: Acyclic enynes undergo a tandem enyne metathesis/cyclopropanation sequence in the presence of Grubbs' 1st generation metathesis catalyst and diazo compounds In practice, the acyclic substrates in the presence of the ruthenium alkylidene first undergo a ring-closing enyne metathesis to generate cyclic 1,3-dienes; then upon addition of a diazo compound, these products are cyclopropanated selectively at the more accessible olefin Overall, the reaction sequence converts acyclic enynes into vinyl cyclopropanes in single operation through two unique ruthenium-catalyzed transformations
83 citations
TL;DR: The utility of Grubbs' 2nd generation metathesis catalyst has been expanded by the development of two tandem olefin meetingathesis/oxidation protocols that provide cis-diols or alpha-hydroxy ketones from simple oleFinic starting materials.
82 citations
75 citations
TL;DR: In this paper, the mechanism of alkyne metathesis catalyzed by W/Mo alkylidyne complexes has been theoretically investigated with the aid of density functional theory calculations.
74 citations
TL;DR: In this paper, the authors highlight some tandem sequences that rely on the conver- sion of the metathesis catalyst to Ru-hydrides, with special emphasis on the tandem ring-closing metatonhesis (RCM)-double-bond isomerization sequence.
Abstract: Tandem sequences consisting of an olefin metathesis step and a subsequent non- metathesis reaction become accessible by organometallic transformations of the Ru-carbene species in situ. This contribution highlights some tandem sequences that rely on the conver- sion of the metathesis catalyst to Ru-hydrides, with special emphasis on the tandem ring- closing metathesis (RCM)-double-bond isomerization sequence.
TL;DR: In this article, the cross-metathesis of methyl maleate (2 ) and ethylene (10 ) using second generation Grubbs catalyst; (1,3-dimesityl-4,5-dihydroimidazol-2-ylidene) (PCy 3 )CI 2 Ru CHPh has been modeled at B3LYP/LACVP ∗ and MPW1K/LCP ∗ levels of theory.
TL;DR: In this article, the reaction of Cl2Ru(PCy3)2(3-phenylindenylidene) with excess pyridine leads to the new pyridine-containing ruthenium-based complex: Cl 2Ru(Pcy3) 2(Py) 2 (3-PNYLID) in good yield, which has been fully characterized and tested in ring closing metathesis.
TL;DR: A method to facilitate regioselective formation of multiple dicarba isosteres of cystine is described and prenylglycine was found to be inert to both Grubbs' and Wilkinson's catalyzed metathesis and hydrogenation, which yielded the second diaminosuberic acid derivative in excellent yield.
Abstract: A method to facilitate regioselective formation of multiple dicarba isosteres of cystine is described. A sequence of ruthenium-catalyzed cross metathesis and rhodium-catalyzed hydrogenation of nonproteinaceous allylglycine derivatives has been developed to achieve high-yielding and unambiguous formation of diaminosuberic acid derivatives. Allylglycine derivatives readily undergo ruthenium-catalyzed metathesis and hydrogenation to yield diaminosuberic acid derivatives in near quantitative yield. Under the same experimental conditions, prenylglycine was found to be inert to both Grubbs' and Wilkinson's catalyzed metathesis and hydrogenation, respectively, but was readily activated for metathesis via cross metathesis with Z-butene. Subsequent cross metathesis of the metathesis-formed crotylglycine derivative, followed by hydrogenation, yielded the second diaminosuberic acid derivative in excellent yield.
TL;DR: Terminal alkyne metathesis has been improved by addition of quinuclidine as an external ligand to the (t-BuO) 3 W≡CBu-t carbyne complex, giving a yield of 80% during hept-1-yne meetathesis.
Abstract: Terminal alkyne metathesis has been improved by addition of quinuclidine as an external ligand to the (t-BuO) 3 W≡CBu-t carbyne complex, giving a yield of 80% during hept-1-yne metathesis. Extension of this system to the co-metathesis of terminal and disubstituted alkynes affords the expected cross-reaction products.
TL;DR: In this paper, a new versatile heterogeneous catalyst for olefin metathesis based on rhenium (VII) oxide supported on organized mesoporous alumina was developed.
Abstract: A new versatile heterogeneous catalyst for olefin metathesis based on rhenium (VII) oxide supported on organized mesoporous alumina was developed. This catalyst is suitable for metathesis of linear olefins, α-, ω-dienes as well as ring-opening metathesis polymerization of cycloalkenes and cross-metathesis of cycloolefins with linear olefins. This catalyst was found to operate under mild reaction conditions and its activity was much higher than that of corresponding catalyst based on conventional alumina. Catalyst can be used repeatedly and can be easily reactivated. Influence of the catalyst pore size on activity as well as selectivity in individual methathesis reactions was established.
TL;DR: In this article, the success of ring closure reactions of substrates having two terminal alkenes through olefin metathesis depends on a number of factors such as catalysts, nature and size of the rings to be formed and the substituents/functional groups present both at the allylic position.
Abstract: Success of ring closure reactions of substrates having two terminal alkenes through olefin metathesis depends on a number of factors such as catalysts, nature and size of the rings to be formed and the substituents/functional groups present on the alkenes as well as at the allylic position. This article presents an overview of these influencing factors with illustrative examples.
TL;DR: Sequential ring-closing metathesis (RCM-Kharasch cyclizations) are promoted by Grubbs catalysts and provide rapid access to bicyclic lactones and lactams as mentioned in this paper.
TL;DR: In this article, water-soluble ruthenium carbene complexes with finely tuned structure and properties in solution were reported, which exhibited great catalytic activity in aqueous miniemulsion ring-opening metathesis polymerization of norbornene.
Abstract: Novel water-soluble ruthenium carbene complexes with finely tuned structure and properties in solution are reported. These ruthenium-based initiators were found to exhibit great catalytic activity in aqueous miniemulsion ring-opening metathesis polymerization of norbornene. Stable particles of polynorbornene could be generated in the 200–250 nm size range stabilized with a nonionic surfactant (polystyrene-b-poly(ethylene oxide)). © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2784–2793, 2006
TL;DR: A ruthenium-based benzylidene complex bearing an O,N-bidentate Schiff base ligand exhibits poor olefin metathesis activity but generates a highly active catalyst system when treated with acidic cocatalysts as mentioned in this paper.
TL;DR: The utility of acyclic diene metathesis (ADMET) polymerization in the synthesis of silicon-carbon hybrid materials is reviewed in this article, where the utility of ADMET is discussed.
Abstract: The utility of acyclic diene metathesis (ADMET) polymerization in the synthesis of silicon–carbon hybrid materials is reviewed. Silicon containing macromolecules are synthesized from organosilicon α,ω-dienes (except those which are divinyl substituted). As an extension of olefin metathesis, ADMET is catalyzed by many transition metal complexes which either initiate the formation of carbene complexes (“ill-defined” catalysts) or by metallacarbene complexes (“well-defined” catalysts). Constant developments of catalytic systems have made this methodology more viable by allowing incorporation of numerous silicon containing functionalities into the polymer's backbone or pendant to it. Divinyl substituted organosilicon derivatives are inert to ADMET conditions; they undergo silylative coupling (SC) polycondensation catalyzed by ruthenium and rhodium complexes yielding metathesis-like products, although this transformation proceeds via a non-metallacarbene mechanism.
TL;DR: The synthesis of highly functionalized fluorinated piperidines is described in this article, where the key step is a ring-closing metathesis reaction involving fluoride-substituted olefins, which leads to cyclic vinyl fluorides.
TL;DR: In this paper, the synthesis and thermal behavior of ADMET polyethylene copolymers are reviewed, as well as other copolymer precursors such as ethylene/propylene (EP), butene/butene (EB), ENE, and ENE copolyms.
Abstract: Acyclic diene metathesis polymerization allows the synthesis of sequenced polyethylene copolymers via step-growth propagation, thereby avoiding the inherent side reactions associated with chain polymerization. Here we review the synthesis and thermal behavior of ADMET polyethylene (PE) as well as ethylene/propylene (EP), ethylene/butene (EB), ethylene/octane (EO), and ethylene/vinyl ether (EVE) copolymers prepared by ADMET.
TL;DR: The ring-closing metathesis (RCM) of dienes that contain at least one participating heteroatom-substituted olefin is reviewed in this paper.
Abstract: The ring-closing metathesis (RCM) of dienes that contain at least one participating heteroatom-substituted olefin is reviewed (olefins substituted with O, N, S, P, Si, B, and halogen atoms will be considered). Efforts have been made to include as many relevant examples of RCM of heteroatom-substituted dienes as possible, but due to the increasing volume of research in this area, an exhaustive coverage is not intended. Attention has focussed on diene RCM reactions catalysed by ruthenium and molybdenum alkylidene complexes, although a brief discussion of some ring-closing reactions of titanium alkylidene species is provided. Other metathesis reactions such as enyne RCM, cross-metathesis and ROMP are not included.
TL;DR: The tandem metathesis/Ireland-Claisen was utilized to access 4-substituted-3,5-cyclohexadiene diol derivatives, which are valuable chiral intermediates for natural product synthesis and proved suitable for chirality transfer originating from chiral propargylic alcohols.
Abstract: To extend the versatility of the ruthenium carbene-promoted enyne metathesis, it was combined with an Ireland ester enolate Claisen rearrangement. This reaction sequence provided conjugated dienes of higher substitution pattern than that obtained through a cross-enyne metathesis alone. The Ireland−Claisen was conducted across both acyclic and cyclic dienes produced from cross-metathesis and methylene-free enyne metathesis, respectively. In the case of cyclodienes, the Ireland−Claisen rearrangement produced s-trans locked dienes which underwent mode-selective ene reaction. The tandem, sequential use of the Ireland−Claisen rearrangement also proved suitable for chirality transfer originating from chiral propargylic alcohols. Last, the tandem metathesis/Ireland−Claisen was utilized to access 4-substituted-3,5-cyclohexadiene diol derivatives, which are valuable chiral intermediates for natural product synthesis. The combination of this pericyclic reaction with a catalytic metathesis reaction extends the versa...
TL;DR: A Hoveyda-type catalyst for olefin metathesis was synthesized and covalently attached via an amide bond to four different solid supports as mentioned in this paper.
TL;DR: In a detailed mechanistic study ESI-MS/MS measurements provided further evidence that the carbene formation is initiated by a unique reaction sequence where the cleavage of the strained olefinic bond starts with phosphine migration forming a cyclic ylide-carbene complex, capable of undergoing metathesis with alternating rhenacyclobutane formation and cycloreversion reactions ("ylide" route).
Abstract: The reaction of [Re(H)(NO)2(PR3)2] complexes (1 a: R = PCy3; 1 b: R = PiPr3) with [H(OEt2)2][BAr(F)4] ([BAr(F)4] = tetrakis{3,5-bis(trifluoromethyl)phenyl}borate) in benzene at room temperature gave the corresponding cations [Re(NO)2(PR3)2][BAr(F)4] (2 a and 2 b). The addition of phenyldiazomethane to benzene solutions of 2 a and 2 b afforded the moderately stable cationic rhenium(I)-benzylidene-dinitrosyl-bis(trialkyl)phosphine complexes 3 a and 3 b as [BAr(F)4]- salts in good yields. The complexes 2 a and 2 b catalyze the ring-opening metathesis polymerization (ROMP) of highly strained nonfunctionalized cyclic olefins to give polymers with relatively high polydispersity indices, high molecular weights and over 80 % Z configuration of the double bonds in the chain backbone. However, these complexes do not show metathesis activity with acyclic olefins. The benzylidene derivatives 3 a and 3 b are almost inactive in ROMP catalysis with norbornene and in olefin metathesis. NMR experiments gave the first hints of the initial formation of carbene complexes from [Re(NO)2(PR3)2][BAr(F)4] (2 a and 2 b) and norbornene. In a detailed mechanistic study ESI-MS/MS measurements provided further evidence that the carbene formation is initiated by a unique reaction sequence where the cleavage of the strained olefinic bond starts with phosphine migration forming a cyclic ylide-carbene complex, capable of undergoing metathesis with alternating rhenacyclobutane formation and cycloreversion reactions ("ylide" route). However, even at an early stage the ROMP propagation route is expected to merge into an "iminate" route by attack by the ylide function on one of the N(NO) atoms followed by phosphine oxide elimination. The formation of phosphine oxide was confirmed by NMR spectroscopy. The proposed mechanism is supported further by detailed DFT calculations.