Metathesis Reactions - University of Waterloo
Thus, we can infer that a reaction occurs if rearrangement of the ions produces one of the above observable results.
Salt metathesis reaction - Wikipedia
Ring-closing metathesis is a variant of the olefin metathesis reaction in which alkylidene moieties are exchanged to form a ring. The most common catalysts for this reaction are complexes of molybdenum or ruthenium.
Ring-opening metathesis polymerization (ROMP) uses metathesis catalysts to generate polymers from cyclic olefins. ROMP is most effective on strained cyclic olefins, because the relief of ring strain is a major driving force for the reaction – cyclooctene and norbornenes are excellent monomers for ROMP, but cyclohexene is very reluctant to form any significant amount of polymer. Norbornenes are favorite monomers for ROMP, as a wide range of monomer functionalities are easily available through Diels-Alder reactions.
Chapter 4 - Metathasis Reactions
H.; Kluger, C., Combining ring-opening metathesis polymerization (ROMP) with Sharpless-type "click" reactions: An easy method for the preparation of side chain functionalized poly(oxynorbornenes).
An oven-dried, 10-mL Schlenk tube equipped with a Teflon valve was charged with a magnetic stir bar, CuI (9.5 mg, 0.050 mmol), and Cs2CO3 (650 mg, 2.0 mmol). The tube was evacuated and refilled with argon. Under a counterflow of argon, 3-iodoaniline (219 mg, 1.0 mmol) and 5-amino-1-pentanol (155 mg, 1.5 mmol) were added followed by DMF (0.5 mL) and 2-isobutyroylcyclohexanone (34 mg, 0.2 mmol). The tube was sealed and the mixture was stirred under argon at ambient temperature (22 °C) for 22 h. After the starting material was consumed, the reaction mixture was diluted with dichloromethane and filtered. The solvent was removed by rotary evaporation, with heating if necessary, to ensure the removal of most of the DMF. The residue was purified by column chromatography on silica gel (EtOAc/hexanes). The product-containing fractions were concentrated by rotary evaporation and dried under high vacuum for at least 1 h to remove residual solvent. N-(3-Aminophenyl)-5-amino-1-pentanol was recovered as a yellow oil (165 mg, 85%): 1H NMR (CDCl3) δ 6.95 (pseudo t, 1H), 6.07–6.04 (m, 2H), 5.94 (pseudo t, 1H), 3.60 (t, J = 7 Hz, 2H), 3.28 (br s, 4H), 3.06 (t, J = 6 Hz, 2H), 1.64–1.53 (m, 4H), 1.47–1.42 (m, 2H); 13C NMR (CDCl3) δ 149.8, 147.7, 130.2, 105.1, 104.3, 99.8, 62.8, 44.1, 32.6, 29.5, 23.6.
an insoluble (solid) precipitate B
Careful balance of catalyst, monomer, and other factors can offer excellent control of the polymer structure. In terms of homogeneous catalysts, most tungsten and molybdenum catalysts (Schrock catalysts) have rapid initiation rates and can produce “living” polymerizations with excellent control of polydispersity and chain tacticity, but the low functional group tolerance limits the monomers available. Ruthenium metathesis catalysts (Grubbs catalysts) tend to have slower initiation rates, often leading to higher polydispersities, but their air stability and greater tolerance for functional groups makes them “user friendly” and enables use of a wide range of functional monomers and additives.
Most ring-closing metathesis reactions are carried out at fairly high dilution of the substrate (10 - 50 mM) with catalyst loadings of 5 - 10 mol % and at slightly elevated temperatures (25 - 110 ºC). Molybdenum catalyst 1 exhibits extreme sensitivity to air and water such that use of a glovebox is ideal. On the other hand, ruthenium catalysts are more stable in air and Schlenck tubes are typically used. Standard workup involves concentration of the reaction mixture, aqueous extraction, and purification via silica gel chromatography, recrystallization, or distillation. Because the standard procedure can leave behind traces of ruthenium, more rigorous workup procedures have been developed that use additional ligands, supercritical fluids, and mesoporous silicates to decrease ruthenium concentrations to extremely low levels.
Metathesis Reactions- - Oklahoma City Community College
METATHESIS | Alkene | Catalysis
From the observation point of view, metathesis reactionscan be further divided into three classes:
C&EN: COVER STORY - OLEFIN METATHESIS: BIG DEAL REACTION
In a precipitation reaction, one of the products formed by the exchange of ions is a (an insoluble solid).
OLEFIN METATHESIS: BIG-DEAL REACTION A ..
It occurs when one of the metathesisproducts is a gas with a low solubility in water, such as H2Sor CO2.
Products - XiMo: Solution driven technology
Ring-closing metathesis has been applied in a large number of syntheses in both academic and industrial contexts. Product rings range in size from five atoms to macrocycles of twenty atoms or more.
Virtual Textbook of Organic Chemistry (MSU)
Unsubstituted α,β-unsaturated esters can likewise coordinate to the metal center and prevent reaction. Including a Lewis acid such as titanium(IV) isopropoxide in the reaction mixture does not interfere with metathesis and prevents coordination to the catalytic metal, enabling reactions of acrylates (Eq. 17).
Thieme E-Books & E-Journals - Synthesis / Issue
Unsaturated lactams are a biochemically important class of heterocycles that can be prepared via ring-closing metathesis. Catalyst 1 is effective in the preparation of five- or six-membered lactams, but crotonamides must be used as unsubstituted α,β-unsaturated amides coordinate to molybdenum, preventing reaction (Eq. 16).
Organometallics (ACS Publications)
Cyclic boronates are formed in cross-metathesis reactions of allylic alcohols and allylboron reagents. Treatment with hydrogen peroxide and sodium hydroxide yields stereodefined allylic diols (Eq. 15).
ThalesNano Nanotechology Inc - Publications
Amides are generally more reactive than amines in arylations due to their greater acidity. Arylation occurs exclusively at nitrogen with the exception of reactions involving pyridones and hindered electrophiles, which can afford substantial amounts of -arylated product. Hydrazides react at the more acidic nitrogen attached to the carbonyl group (Eq. 12).
Click Chemistry Publications - Scripps Research Institute
Azoles are highly effective nucleophiles in copper-catalyzed amination reactions, with the important exception of acidic tetrazoles (Eq. 11). Heterocycles must strike a balance between acidity of the azole, which is important for copper-azolate formation in the early stages of the mechanism, and nucleophilicity of the azolate, which is important for the C–N bond-forming step. Mixtures of constitutionally isomeric -arylated products can be a limitation of the reaction in some cases, but -arylation is rarely an issue.
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