Metathesis Of Terminal Olefins Research Articles

Probing Catalyst Degradation in Metathesis of Internal Olefins: Expanding Access to Amine-Tagged ROMP Polymers.

Ruthenium-promoted ring-opening metathesis polymerization (ROMP) offers potentially powerful routes to amine-functionalized polymers with antimicrobial, adhesive, and self-healing properties. However, amines readily degrade the methylidene and unsubstituted ruthenacyclobutane intermediates formed in metathesis of terminal olefins. Examined herein is the relevance of these decomposition pathways to ROMP (i.e., metathesis of internal olefins) by the third-generation Grubbs catalyst. Primary alkylamines rapidly quench polymerization via fast adduct formation, followed by nucleophilic abstraction of the propagating alkylidene. Bulkier, Brønsted-basic amines are less aggressive: attack competes only for slow polymerization or strong bases (e.g., DBU). Added HCl limits degradation, as demonstrated by the successful ROMP of an otherwise intractable methylamine monomer.

Mesomeric Acceleration Counters Slow Initiation of Ruthenium-CAAC Catalysts for Olefin Metathesis (CAAC = Cyclic (Alkyl)(Amino) Carbene).

Ruthenium catalysts bearing cyclic (alkyl)(amino)carbene (CAAC) ligands can attain very high productivities in olefin metathesis, owing to their resistance to unimolecular decomposition. Because the propagating methylidene species RuCl2(CAAC)(=CH2) is extremely susceptible to bimolecular decomposition, however, turnover numbers in the metathesis of terminal olefins are highly sensitive to catalyst concentration, and hence loadings. Understanding how, why, and how rapidly the CAAC complexes partition between the precatalyst and the active species is thus critical. Examined in a dual experimental-computational study are the rates and basis of initiation for phosphine-free catalysts containing the leading CAAC ligand C1 Ph , in which a CMePh group α to the carbene carbon helps retard degradation. The Hoveyda-class complex HC1 Ph (RuCl2(L)(=CHAr), where L = C1 Ph , Ar = C6H3-2-O i Pr-5-R; R = H) is compared with its nitro-Grela analogue (nG-C1 Ph ; R = NO2) and the classic Hoveyda catalyst HII (L = H2IMes; R = H). t-Butyl vinyl ether (tBuVE) was employed as substrate, to probe the reactivity of these catalysts toward olefins of realistic bulk. Initiation is ca. 100× slower for HC1 Ph than HII in C6D6, or 44× slower in CDCl3. The rate-limiting step for the CAAC catalyst is cycloaddition; for HII, it is tBuVE binding. Initiation is 10-13× faster for nG-C1 Ph than HC1 Ph in either solvent. DFT analysis reveals that this rate acceleration originates in an overlooked role of the nitro group. Rather than weakening the Ru-ether bond, as widely presumed, the NO2 group accelerates the ensuing, rate-limiting cycloaddition step. Faster reaction is caused by long-range mesomeric effects that modulate key bond orders and Ru-ligand distances, and thereby reduce the trans effect between the carbene and the trans-bound alkene in the transition state for cycloaddition. Mesomeric acceleration may plausibly be introduced via any of the ligands present, and hence offers a powerful, tunable control element for catalyst design.

A Tungsten Oxo Alkylidene Supported on Sulfated Zirconium Oxide for Olefin Metathesis

The reaction of W(O)(Adene)(2,5-dimethylpyrrolide)2 (1; Adene = 2-adamantylidene) and sulfated zirconium oxide (SZO) results in the formation of [W(O)(Adene)(2,5-dimethylpyrrolide)][SZO] (1@SZO). 1@SZO reacts with 13C-labeled ethylene to give 1-13C-adamantylethylene and square pyramidal [W(O)(CH2)3(2,5-dimethylpyrrolide)][SZO] (2) as major reaction products; small amounts of [13C]propene and [W(O)(H2C═CH2)(2,5-dimethylpyrrolide)][SZO] (3) also form in this reaction. 1@SZO is active in olefin metathesis of terminal olefins, including methyl 10-undecenoate, to give the thermodynamic E-olefin product; and also catalyzes the direct formation of propylene from ethylene.

Silica‐Supported Molybdenum Oxo Alkylidenes: Bridging the Gap between Internal and Terminal Olefin Metathesis

AbstractGrafting a molybdenum oxo alkylidene on silica (partially dehydroxylated at 700 °C) affords the first example of a well‐defined silica‐supported Mo oxo alkylidene, which is an analogue of the putative active sites in heterogeneous Mo‐based metathesis catalysts. In contrast to its tungsten analogue, which shows poor activity towards terminal olefins because of the formation of a stable off‐cycle metallacyclobutane intermediate, the Mo catalyst shows high metathesis activity for both terminal and internal olefins that is consistent with the lower stability of Mo metallacyclobutane intermediates. This Mo oxo metathesis catalyst also outperforms its corresponding neutral silica‐supported Mo and W imido analogues.

Silica-Supported Molybdenum Oxo Alkylidenes: Bridging the Gap between Internal and Terminal Olefin Metathesis.

Grafting a molybdenum oxo alkylidene on silica (partially dehydroxylated at 700 °C) affords the first example of a well-defined silica-supported Mo oxo alkylidene, which is an analogue of the putative active sites in heterogeneous Mo-based metathesis catalysts. In contrast to its tungsten analogue, which shows poor activity towards terminal olefins because of the formation of a stable off-cycle metallacyclobutane intermediate, the Mo catalyst shows high metathesis activity for both terminal and internal olefins that is consistent with the lower stability of Mo metallacyclobutane intermediates. This Mo oxo metathesis catalyst also outperforms its corresponding neutral silica-supported Mo and W imido analogues.

Highly selective macrocyclic ring-closing metathesis of terminal olefins in non-chlorinated solvents at low dilution

New ruthenium complexes featuring two unsymmetrical NHCs proved to be highly selective in macrocyclic RCM performed in green solvents at low dilution.

Promoting Terminal Olefin Metathesis with a Supported Cationic Molybdenum Imido Alkylidene N‐Heterocyclic Carbene Catalyst

AbstractSilica‐supported cationic Mo‐imido alkylidene N‐heterocyclic carbene catalysts, prepared by surface organometallic chemistry, display contrasting olefin metathesis activity for terminal and internal olefins. The high metathesis activity towards terminal alkenes is attributed to the strong σ‐donating property of the NHC ancillary ligand, which disfavors the formation of the parent square‐planar metallacyclobutane, an off‐cycle reaction intermediate resulting from the reaction with ethylene, one of the metathesis products. This tailored ligand environment also allowed the first trigonal bipyramidal (TBP) metallacyclobutane reaction intermediate for supported Mo metathesis catalysts to be identified.

Promoting Terminal Olefin Metathesis with a Supported Cationic Molybdenum Imido Alkylidene N-Heterocyclic Carbene Catalyst.

Silica-supported cationic Mo-imido alkylidene N-heterocyclic carbene catalysts, prepared by surface organometallic chemistry, display contrasting olefin metathesis activity for terminal and internal olefins. The high metathesis activity towards terminal alkenes is attributed to the strong σ-donating property of the NHC ancillary ligand, which disfavors the formation of the parent square-planar metallacyclobutane, an off-cycle reaction intermediate resulting from the reaction with ethylene, one of the metathesis products. This tailored ligand environment also allowed the first trigonal bipyramidal (TBP) metallacyclobutane reaction intermediate for supported Mo metathesis catalysts to be identified.

Bimolecular Coupling as a Vector for Decomposition of Fast-Initiating Olefin Metathesis Catalysts.

The correlation between rapid initiation and rapid decomposition in olefin metathesis is probed for a series of fast-initiating, phosphine-free Ru catalysts: the Hoveyda catalyst HII, RuCl2(L)(═CHC6H4- o-O iPr); the Grela catalyst nG (a derivative of HII with a nitro group para to O iPr); the Piers catalyst PII, [RuCl2(L)(═CHPCy3)]OTf; the third-generation Grubbs catalyst GIII, RuCl2(L)(py)2(═CHPh); and dianiline catalyst DA, RuCl2(L)( o-dianiline)(═CHPh), in all of which L = H2IMes = N,N'-bis(mesityl)imidazolin-2-ylidene. Prior studies of ethylene metathesis have established that various Ru metathesis catalysts can decompose by β-elimination of propene from the metallacyclobutane intermediate RuCl2(H2IMes)(κ2-C3H6), Ru-2. The present work demonstrates that in metathesis of terminal olefins, β-elimination yields only ca. 25-40% propenes for HII, nG, PII, or DA, and none for GIII. The discrepancy is attributed to competing decomposition via bimolecular coupling of methylidene intermediate RuCl2(H2IMes)(═CH2), Ru-1. Direct evidence for methylidene coupling is presented, via the controlled decomposition of transiently stabilized adducts of Ru-1, RuCl2(H2IMes)Ln(═CH2) (Ln = py n'; n' = 1, 2, or o-dianiline). These adducts were synthesized by treating in situ-generated metallacyclobutane Ru-2 with pyridine or o-dianiline, and were isolated by precipitating at low temperature (-116 or -78 °C, respectively). On warming, both undergo methylidene coupling, liberating ethylene and forming RuCl2(H2IMes)Ln. A mechanism is proposed based on kinetic studies and molecular-level computational analysis. Bimolecular coupling emerges as an important contributor to the instability of Ru-1, and a potentially major pathway for decomposition of fast-initiating, phosphine-free metathesis catalysts.

Benchmarked Intrinsic Olefin Metathesis Activity: Mo vs. W

Combining Surface Organometallic Chemistry with rigorous olefin purification protocol allows evaluating and comparing the intrinsic activities of Mo and W olefin metathesis catalysts towards different types of olefin substrates. While well‐defined silica‐supported Mo and W imido‐alkylidenes show very similar activities in metathesis of internal olefins, Mo catalysts systematically outperform their W analogs in metathesis of terminal olefins, consistent with the formation of stable unsubstituted W metallacyclobutanes in the presence of ethylene. However, Mo catalysts are more prone to induce olefin isomerization, in particular when ethylene is present, probably because of their propensity to undergo more easily reduction processes.

A General Decomposition Pathway for Phosphine-Stabilized Metathesis Catalysts: Lewis Donors Accelerate Methylidene Abstraction.

Sterically accessible Lewis donors are shown to accelerate decomposition during catalysis, for a broad range of Grubbs-class metathesis catalysts. These include benzylidene derivatives RuCl2(NHC)(PCy3)(═CHPh) (Ru-2: NHC = H2IMes, a; IMes, b; H2IPr, c; IPr, d; H2ITol, e) and indenylidene complexes RuCl2(NHC)(PCy3)(═C15H10) (NHC = H2IMes, Ru-2f; IMes, Ru-2g). All of these precatalysts form methylidene complex RuCl2(NHC)(═CH2) Ru-3 as the active species in metathesis of terminal olefins, and generate RuCl2(NHC)(PCy3)(═CH2) Ru-4 as the catalyst resting state. On treatment with a 10-fold excess of pyridine, Ru-4a and Ru-4b decomposed within minutes in solution at RT, eliminating [MePCy3]Cl A by net loss of three ligands (PCy3, methylidene, and one chloride), and a mesityl proton. In comparison, loss of A from Ru-4a in the absence of a donor requires up to 3 days at 55 °C. The σ-alkyl intermediate RuCl2(13CH2PCy3)(NHC) (py)2 resulting from nucleophilic attack of free PCy3 on the methylidene ligand was undetectable for the H2IMes system, but was spectroscopically observable for the IMes system. The relevance of this pathway to decomposition of catalysts Ru-2a-g was demonstrated by assessing the impact of pyridine on the in situ-generated methylidene species. Slow initiation (as observed for the indenylidene catalysts) did not protect against methylidene abstraction. Importantly, studies with Ru-4a and Ru-4b indicated that weaker donors (THF, MeCN, DMSO, MeOH, and even H2O) likewise promote this pathway, at rates that increase with donor concentration, and severely degrade catalyst productivity in RCM, even for a readily cyclized substrate. In all cases, A was the sole or major 31P-containing decomposition product. For DMSO, a first-order dependence of decomposition rates on DMSO concentration was established. This behavior sends a warning about the use of phosphine-stabilized metathesis catalysts in donor solvents, or with substrates bearing readily accessible donor sites. Addition of pyridine to RuCl2(H2IMes)(PCy3)(═CHMe) did not result in ethylidene abstraction, indicating that this decomposition pathway can be inhibited by use of substrates in which the olefin bears a β-methyl group.

Convergent Synthesis of a Metal–Organic Framework Supported Olefin Metathesis Catalyst

Synthesis of a metal–organic framework (MOF)-supported olefin metathesis catalyst has been accomplished for the first time following a new, convergent approach where an aldehyde-functionalized derivative of Hoveyda’s recently reported ruthenium catecholate olefin metathesis catalyst is condensed with an amine-functionalized IRMOF-74-III. The resulting material, denoted MOF-Ru, has well-defined, catalytically active ruthenium centers confined within channels having a ca. 20 A diameter. MOF-Ru is a recyclable, single-site catalyst for self-cross-metathesis and ring-closing metathesis of terminal olefins. Comparison of this heterogeneous catalyst with a homogeneous analogue shows different responses to substrate size and shape suggestive of confinement effects. The MOF-Ru catalyst also displays greater resistance to double-bond migration that can be attributed to greater catalyst stability. For the preparation of well-defined, single-site heterogeneous catalysts where catalyst purity is essential, the conver...

Homogeneous catalyst systems with organosilicon components for olefin metathesis

Two silicon-containing catalyst systems for the olefin metathesis reaction are described. The first system, WCl 6/Ph 2SiH 2, is active for all kinds of olefinic substrates: acyclic, cyclic and functionalized olefins, and alkadienes. The second system, W(CO) 6/Ph 2SiH 2, is active for the metathesis of terminal olefins, but only under UV irradiation. Upon reaction between the catalyst components, a tungsten–silylene intermediate is formed as the precursor of the active species for metathesis. The product of a [2+2] cycloaddition of the tungsten–silylene complex was isolated. It showed catalytic activity for the metathesis of 1-hexene under UV irradiation, or at elevated temperature, when tungsten–silylene species could be generated from [W(CO) 4] 2[μ 2-Si(C 6H 5) 2] 2. This is the first example of olefin metathesis with metal–silylene activation.

Relative Reaction Rates of Olefin Substrates with Ruthenium(II) Carbene Metathesis Initiators1

The metathesis of terminal olefins having different steric bulk and different geometries as well as electronically different para-substituted styrenes was studied with the ruthenium-based metathesis initiators trans-(PCy3)2Cl2RuCHR. Bulkier olefins were found to react slower, and trans internal olefins were found to be slower than cis. The kinetic product of all reactions was found to be the alkylidene rather than the methylidene. Observed effects were used to explain the mechanism of ring-opening cross metathesis. No linear electronic effects were observed.

Acyclic diene metathesis (ADMET) polymerization: the synthesis of unsaturated polyesters

The first acyclic diene metathesis (ADMET) polymerization using the molybdenum catalyst Mo(CHCMe 2 R)(N-2,6-C 6 H 3 -i-Pr 2 )[OCCH 3 (CF 3 ) 2 ] 2 (R=Me, Ph) is presented. This catalyst is much faster in the metathesis of terminal olefins than its tungsten counterpart. 1,4-Benzenedicarboxylic bis(1-hexenyl) ester, 1,4-benzenedicarboxylic bis(1-pentenyl) ester, 1,4-benzenedicarboxylic bis(1-butenyl) ester, and 1-hexenyl 1-pentenoate succesfully undergo ADMET homopolymerization to produce the unsaturated polyesters [OCOPHCOO(CH 2 ) m CH=CH(CH 2 ) m ] n (m= 2,3,4) and [OCO(CH 2 ) 2 CH=CH(CH 2 ) 4 ] n , respectively

The photoinduced metathesis of olefin catalyzed by W(CO) 5L-AX n system

In the photocatalytic system containing tungsten compounds of the type W(CO) 5L (L = CO, py, PPh 3, Cl −) and Group IIIb and IVab element halides (AX n ), the metathesis of internal and terminal olefins was investigated. The terminal olefin metathesis reaction is accompanied by double bond migration yielding the internal olefins, which undergo co-metathesis with the initial olefins. Substitution of tungsten by molybdenum or chromium favours the isomerization reaction.

ChemInform Abstract: THE CHEMISTRY OF BENT BONDS. 51. THE RELATION OF POLARIZATION IN METAL‐CARBENE COMPLEXES TO THE DEGENERATE METATHESIS OF TERMINAL OLEFINS

Chemischer InformationsdienstVolume 8, Issue 15 Organoelement Compounds ChemInform Abstract: THE CHEMISTRY OF BENT BONDS. 51. THE RELATION OF POLARIZATION IN METAL-CARBENE COMPLEXES TO THE DEGENERATE METATHESIS OF TERMINAL OLEFINS P. G. GASSMAN, Search for more papers by this authorT. H. JOHNSON, Search for more papers by this author P. G. GASSMAN, Search for more papers by this authorT. H. JOHNSON, Search for more papers by this author First published: April 12, 1977 https://doi.org/10.1002/chin.197715284Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onEmailFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume8, Issue15April 12, 1977 RelatedInformation

ChemInform Abstract: OLEFIN METATHESIS BY PYRIDINEPENTACARBONYLMOLYBDENUM

AbstractFür die Metathese endständiger Olefine werden Pyridinpentacarbonylmolybdän, Äthylaluminiumdichlorid und Tetrabutylammoniumchlorid als Katalysatorsystem eingesetzt.

The chemistry of bent bonds. 51. The relation of polarization in metal-carbene complexes to the degenerate metathesis of terminal olefins

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTThe chemistry of bent bonds. 51. The relation of polarization in metal-carbene complexes to the degenerate metathesis of terminal olefinsPaul G. Gassman and Thomas H. JohnsonCite this: J. Am. Chem. Soc. 1977, 99, 2, 622–623Publication Date (Print):January 1, 1977Publication History Published online1 May 2002Published inissue 1 January 1977https://doi.org/10.1021/ja00444a058RIGHTS & PERMISSIONSArticle Views66Altmetric-Citations12LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (271 KB) Get e-Alerts Get e-Alerts

Olefin metathesis by pyridinepentacarbonylmolybdenum

Pyridinepentacarbonylmolybdenum with ethylaluminium dichloride and tetrabutylammonium chloride constitute a catalyst system for the metathesis of terminal olefins; evidence for a co-ordinated carbene-initiated process is presented, and the nature of the co-ordinated carbene formed initially is found to be solvent dependent.