A Rapid and Simple Cleanup Procedure for Metathesis Reactions

Galan, Brandon R.; Kalbarczyk, Kyle P.; Szczepankiewicz, Steven H.; Keister, and Jerome B.; Diver, Steven T.

doi:10.1021/ol0631399

Cited by 136 publications

(87 citation statements)

References 8 publications

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“…Other approaches include the isocyanide-promoted degradation used by Diver and co-workers 33 . All these methods require a post-polymerization purification step along with an excess of added chemical agents, which makes ROMP commercially less attractive.…”

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confidence: 99%

Catalytic living ring-opening metathesis polymerization

Nagarkar

Kilbinger

2015

Nature Chem

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In living ring-opening metathesis polymerization (ROMP), a transition-metal-carbene complex polymerizes ring-strained olefins with very good control of the molecular weight of the resulting polymers. Because one molecule of the initiator is required for each polymer chain, however, this type of polymerization is expensive for widespread use. We have now designed a chain-transfer agent (CTA) capable of reducing the required amount of metal complex while still maintaining full control over the living polymerization process. This new method introduces a degenerative transfer process to ROMP. We demonstrate that substituted cyclohexene rings are good CTAs, and thereby preserve the 'living' character of the polymerization using catalytic quantities of the metal complex. The resulting polymers show characteristics of a living polymerization, namely narrow molecular-weight distribution, controlled molecular weights and block copolymer formation. This new technique provides access to well-defined polymers for industrial, biomedical and academic use at a fraction of the current costs and significantly reduced levels of residual ruthenium catalyst. In olefin metathesis reactions, olefinic bonds are rearranged with the help of a transition-metal catalyst 1,2 . In the early days following the discovery of this reaction, ill-defined catalysts 3 were used to carry out this transformation. After Herisson and Chauvin 4 had proposed a reaction mechanism, the olefin metathesis reaction was better understood and soon gained much popularity. Typical catalysts used for olefin metathesis reactions include those based on ruthenium (developed mainly by the Grubbs group 5 ), tungsten and molybdenum (developed mainly by the Schrock group 6 ). Owing to the low oxophilicity of ruthenium compared to those of molybdenum and tungsten, the ruthenium metathesis catalysts (commonly known as Grubbs' catalysts) are more tolerant towards many polar functional groups and residual impurities, as well as to water 7 . Therefore, these catalysts are the catalysts of choice in highly functional organic chemistry transformations as well as for the majority of metathesis polymerizations carried out today. Catalysts G1 (first generation) and G3 (third generation) are the most widely used ruthenium initiators for ring-opening metathesis polymerization (ROMP). In comparison to the G1 initiator, the third-generation catalyst G3 exhibits very fast initiation and propagation rates, and thereby gives polymers with very narrow dispersities and an excellent control over their molecular weights. Owing to its superior stability as well as the favourable polymerization kinetics, the third-generation Grubbs' catalyst G3 was used for this work. ROMP is a polymerization technique that uses the metathesis of cyclic olefins to synthesize linear polymers. Depending on the structure of the monomer, such polymerizations can be controlled perfectly to give polymers with a narrow molecular weight distribution and a controlled average molecular weight. Ring-strained monomers, li...

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confidence: 99%

Catalytic living ring-opening metathesis polymerization

Nagarkar

Kilbinger

2015

Nature Chem

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“…The main advantage of the procedure is its very rapid reaction rate (1 min is typical), and the use of small amounts of isocyanide KO 2 CCH 2 NC (40-50 mol%) and that it results in a demonstrated 'quench' of carbenic activity for a wide variety of Grubbs carbenes. 39 The 'quench' destroys metathesis activity completely and arrests any further metathetic processes. The quench of carbene activity is accomplished by transferring the carbene into one of the aromatic rings of the NHC ligand (e.g., in complex 2) 39,40 : an intramolecular Buchner cyclopropanation, which is followed by a norcaradiene-to-cycloheptatriene rearrangement.…”

Section: Quench and Removal Of Rutheniummentioning

confidence: 99%

“…Notably, a free hydroxyl group in the alkyne reactant is not permitted in this reaction. The reactions were quenched using the polar isocyanide 39 that assisted in the purification of products.…”

Section: Cross-eym With 1-alkenesmentioning

confidence: 99%

5.27 Ene–Yne Metathesis

Diver

Clark

2014

Comprehensive Organic Synthesis II

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“…Effective cleanup procedures provided by these methods are often associated with high loading of ruthenium scavengers and long processing times. Diver and co-workers 9 have recently demonstrated a novel method for quenching Grubbs' carbene complexes via ligand insertion with a polar isocyanide (NCCH 2 CO 2 Et). Although this new isocyanide provides a faster and more effective method for deactivating many commonly used metathesis catalysts, it also has limitations, such as limited tolerance towards functional groups, toxicity, and the lack of commercial availability, which may hinder its wide application.…”

Section: Introductionmentioning

confidence: 99%