Inhibitory Effect of Ethylene in Ene–Yne Metathesis: The Case for Ruthenacyclobutane Resting States

Gregg, Timothy M.; Keister, Jerome B.; Diver, Steven T.

doi:10.1021/ja4085012

Cited by 17 publications

(12 citation statements)

References 37 publications

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“…Once a stable metal carbene is formed in enyne metathesis, the catalytically active RuCH 2 species can be regenerated by an ethene-induced conversion, which is known as the Mori effect . Diver et al showed that the presence of ethene in enyne metathesis leads to a ruthenacyclobutane resting state and lower catalytic efficiency …”

Section: Introductionmentioning

confidence: 99%

The Initiation Reaction of Hoveyda–Grubbs Complexes with Ethene

2019

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The initiation reactions of the three Hoveyda–Grubbs complexes (GH(H), GH(4-NO 2 ), and GH(5-NO 2 )) with ethene were studied via UV–vis spectroscopy. The unsubstituted complex GH(H) initiates approximately 5 times slower with ethene than with 1-hexene, and the electron-deficient GH(4-NO 2 ) and GH(5-NO 2 ) initiates 1.2 and 1.7 times slower with ethene than with 1-hexene. A detailed multiwavelength analysis of the absorbance–time traces reveals the multistep nature of the reaction of the Hoveyda–Grubbs complexes with ethene. In addition to the established rate constant k 1 (being first order in ethene), two additional, c(olefin) independent reactions k 2 and k 3 were identified: k 2 depends on the nature of the GH precatalyst, while k 3 is nearly independent of the precatalyst. The reaction associated with k 1 precedes the faster k 2 leading to low stationary concentration of an intermediate formed from the respective Hoveyda–Grubbs complex and ethene, corresponding to a postinitiation species.

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Section: Introductionmentioning

confidence: 99%

The Initiation Reaction of Hoveyda–Grubbs Complexes with Ethene

2019

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“…Commercially available alkyne 3 is first alkylated using a previously published procedure, 25 and the resulting alkyne 4 is converted to THP-DMTB ( 2 ) through an enyne metathesis conducted under 1 atm of ethylene gas using Grubbs’ second generation catalyst. While previous studies have used higher catalyst loadings and elevated temperatures for similar substrates, 26 , 27 the conditions employed here for the synthesis of THP-DMTB ( 2 ) are unexpectedly efficient and can be conducted on a multigram scale. The hydrolysis of THP-DMTB ( 2 ) to the desired alcohol 1 was accomplished with boric acid in refluxing ethanol which gave DMTB in 70% yield with a minor amount (6%) of the protodesilylated alcohol product.…”

Section: Resultsmentioning

confidence: 98%

Tetramethyleneethane Equivalents: Recursive Reagents for Serialized Cycloadditions

2015

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New reactions and reagents that allow for multiple bond-forming events per synthetic operation are required to achieve structural complexity and thus value with step-, time-, cost-, and waste-economy. Here we report a new class of reagents that function like tetramethyleneethane (TME), allowing for back-to-back [4 + 2] cycloadditions, thereby amplifying the complexity-increasing benefits of Diels–Alder and metal-catalyzed cycloadditions. The parent recursive reagent, 2,3-dimethylene-4-trimethylsilylbutan-1-ol (DMTB), is readily available from the metathesis of ethylene and THP-protected 4-trimethylsilylbutyn-1-ol. DMTB and related reagents engage diverse dienophiles in an initial Diels–Alder or metal-catalyzed [4 + 2] cycloaddition, triggering a subsequent vinylogous Peterson elimination that recursively generates a new diene for a second cycloaddition. Overall, this multicomponent catalytic cascade produces in one operation carbo- and heterobicyclic building blocks for the synthesis of a variety of natural products, therapeutic leads, imaging agents, and materials. Its application to the three step synthesis of a new solvatochromic fluorophore, N-ethyl(6-N,N-dimethylaminoanthracene-2,3-dicarboximide) (6-DMA), and the photophysical characterization of this fluorophore are described.

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“…The internal alkyne 15 showed a t 1/2 = 72 s (apparent first-order k obs , 0.08 M alkyne, 2 M 1-hexene, 0.1 mM Ru1 ). This data provides an interesting comparison considering that the different alkynes have different overall reaction orders and different rate-determining steps. , …”

Section: Resultsmentioning

confidence: 99%

“…The vinyl carbene has been calculated to be a stable carbene intermediate (as compared to [Ru]CHR), and the alkyne insertion step is an irreversible elementary step . The rates of internal alkynes or EYM promoted by phosphine-free initiators (e.g., Ru1 , Ru2 ) have not been studied …”

Section: Introductionmentioning

confidence: 99%

From Resting State to the Steady State: Mechanistic Studies of Ene–Yne Metathesis Promoted by the Hoveyda Complex

2016

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The kinetics of intermolecular ene-yne metathesis (EYM) with the Hoveyda precatalyst (Ru1) has been studied. For 1-hexene metathesis with 2-benzoyloxy-3-butyne, the experimental rate law was determined to be first-order in 1-hexene (0.3-4 M), first-order in initial catalyst concentration, and zero-order for the terminal alkyne. At low catalyst concentrations (0.1 mM), the rate of precatalyst initiation was observed by UV-vis and the alkyne disappearance was observed by in situ FT-IR. Comparison of the rate of precatalyst initiation and the rate of EYM shows that a low, steady-state concentration of active catalyst is rapidly produced. Application of steady-state conditions to the carbene intermediates provided a rate treatment that fit the experimental rate law. Starting from a ruthenium alkylidene complex, competition between 2-isopropoxystyrene and 1-hexene gave a mixture of 2-isopropoxyarylidene and pentylidene species, which were trappable by the Buchner reaction. By varying the relative concentration of these alkenes, 2-isopropoxystyrene was found to be 80 times more effective than 1-hexene in production of their respective Ru complexes. Buchner-trapping of the initiation of Ru1 with excess 1-hexene after 50% loss of Ru1 gave 99% of the Buchner-trapping product derived from precatalyst Ru1. For the initiation process, this shows that there is an alkene-dependent loss of precatalyst Ru1, but this does not directly produce the active catalyst. A faster initiating precatalyst for alkene metathesis gave similar rates of EYM. Buchner-trapping of ene-yne metathesis failed to deliver any products derived from Buchner insertion, consistent with rapid decomposition of carbene intermediates under ene-yne conditions. An internal alkyne, 1,4-diacetoxy-2-butyne, was found to obey a different rate law. Finally, the second-order rate constant for ene-yne metathesis was compared to that previously determined by the Grubbs second-generation carbene complex: Ru1 was found to promote ene-yne metathesis 62 times faster at the same initial precatalyst concentration.

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Inhibitory Effect of Ethylene in Ene–Yne Metathesis: The Case for Ruthenacyclobutane Resting States

Cited by 17 publications

References 37 publications

The Initiation Reaction of Hoveyda–Grubbs Complexes with Ethene

The Initiation Reaction of Hoveyda–Grubbs Complexes with Ethene

Tetramethyleneethane Equivalents: Recursive Reagents for Serialized Cycloadditions

From Resting State to the Steady State: Mechanistic Studies of Ene–Yne Metathesis Promoted by the Hoveyda Complex

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