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Article: Methylene transfer or carbometalation? A theoretical study to determine the mechanism of lithium carbenoid-promoted cyclopropanation reactions in aggregation and solvation states

TitleMethylene transfer or carbometalation? A theoretical study to determine the mechanism of lithium carbenoid-promoted cyclopropanation reactions in aggregation and solvation states
Authors
Issue Date2007
PublisherAmerican Chemical Society. The Journal's web site is located at http://pubs.acs.org/joc
Citation
Journal Of Organic Chemistry, 2007, v. 72 n. 3, p. 848-860 How to Cite?
Abstract(Chemical Equation Presented) Density functional theory calculations for the lithium carbenoid-promoted cyclopropanations in aggregation and solvation states are presented in order to investigate the controversy of the mechanistic dichotomy, that is, the methylene-transfer mechanism and the carbometalation mechanism. The methylene-transfer mechanism represents the reaction reality, whereas the carbometalation pathway does not appear to compete significantly with the methylene-transfer pathway and should be ruled out as a major factor. A simple model calculation for monomeric lithium carbenoid-promoted cyclopropanations with ethylene in the gas phase is not sufficient to reflect the reaction conditions accurately or to determine the reaction mechanism since its result is inconsistent with the experimental facts. The aggregated lithium carbenoids are the most probable reactive species in the reaction system. The calculated reaction barriers of the methylene-transfer pathways are 10.1 and 8.0 kcal/mol for the dimeric (LiCH2F)2 and tetrameric (LiCH2F)4 species, respectively, compared with the reaction barrier of 16.0 kcal/mol for the monomeric LiCH2F species. In contrast, the reaction barriers of the carbometalation pathways are 26.8 kcal/mol for the dimeric (LiCH2F)2 and 33.9 kcal/mol for the tetrameric (LiCH2F)4 species, compared with the reaction barrier of 12.5 kcal/mol for the monomeric LiCH2F species. The effects of solvation were investigated by explicit coordination of the solvent molecules to the lithium centers. This solvation effect is found to enhance the methylene-transfer pathway, while it is found to impede the carbometalation pathway instead. The combined effects of the aggregation and solvation lead to barriers to reaction in the range of 7.2-9.0 kcal/mol for lithium carbenoid-promoted cyclopropanation reactions along the methylene-transfer pathway. Our computational results are in good agreement with the experimental observations. © 2007 American Chemical Society.
Persistent Identifierhttp://hdl.handle.net/10722/69547
ISSN
2015 Impact Factor: 4.785
2015 SCImago Journal Rankings: 2.095
ISI Accession Number ID
References

 

DC FieldValueLanguage
dc.contributor.authorKe, Zen_HK
dc.contributor.authorZhao, Cen_HK
dc.contributor.authorPhillips, DLen_HK
dc.date.accessioned2010-09-06T06:14:40Z-
dc.date.available2010-09-06T06:14:40Z-
dc.date.issued2007en_HK
dc.identifier.citationJournal Of Organic Chemistry, 2007, v. 72 n. 3, p. 848-860en_HK
dc.identifier.issn0022-3263en_HK
dc.identifier.urihttp://hdl.handle.net/10722/69547-
dc.description.abstract(Chemical Equation Presented) Density functional theory calculations for the lithium carbenoid-promoted cyclopropanations in aggregation and solvation states are presented in order to investigate the controversy of the mechanistic dichotomy, that is, the methylene-transfer mechanism and the carbometalation mechanism. The methylene-transfer mechanism represents the reaction reality, whereas the carbometalation pathway does not appear to compete significantly with the methylene-transfer pathway and should be ruled out as a major factor. A simple model calculation for monomeric lithium carbenoid-promoted cyclopropanations with ethylene in the gas phase is not sufficient to reflect the reaction conditions accurately or to determine the reaction mechanism since its result is inconsistent with the experimental facts. The aggregated lithium carbenoids are the most probable reactive species in the reaction system. The calculated reaction barriers of the methylene-transfer pathways are 10.1 and 8.0 kcal/mol for the dimeric (LiCH2F)2 and tetrameric (LiCH2F)4 species, respectively, compared with the reaction barrier of 16.0 kcal/mol for the monomeric LiCH2F species. In contrast, the reaction barriers of the carbometalation pathways are 26.8 kcal/mol for the dimeric (LiCH2F)2 and 33.9 kcal/mol for the tetrameric (LiCH2F)4 species, compared with the reaction barrier of 12.5 kcal/mol for the monomeric LiCH2F species. The effects of solvation were investigated by explicit coordination of the solvent molecules to the lithium centers. This solvation effect is found to enhance the methylene-transfer pathway, while it is found to impede the carbometalation pathway instead. The combined effects of the aggregation and solvation lead to barriers to reaction in the range of 7.2-9.0 kcal/mol for lithium carbenoid-promoted cyclopropanation reactions along the methylene-transfer pathway. Our computational results are in good agreement with the experimental observations. © 2007 American Chemical Society.en_HK
dc.languageengen_HK
dc.publisherAmerican Chemical Society. The Journal's web site is located at http://pubs.acs.org/jocen_HK
dc.relation.ispartofJournal of Organic Chemistryen_HK
dc.subject.meshAlgorithmsen_HK
dc.subject.meshCyclopropanes - chemistryen_HK
dc.subject.meshDimerizationen_HK
dc.subject.meshEthylenes - chemistryen_HK
dc.subject.meshLithium Compounds - chemistryen_HK
dc.subject.meshMolecular Conformationen_HK
dc.subject.meshOrganometallic Compounds - chemistryen_HK
dc.subject.meshSolvents - chemistryen_HK
dc.subject.meshThermodynamicsen_HK
dc.titleMethylene transfer or carbometalation? A theoretical study to determine the mechanism of lithium carbenoid-promoted cyclopropanation reactions in aggregation and solvation statesen_HK
dc.typeArticleen_HK
dc.identifier.openurlhttp://library.hku.hk:4550/resserv?sid=HKU:IR&issn=0022-3263&volume=72&spage=848&epage=860&date=2007&atitle=Methylene+Transfer+or+Carbometalation?+A+Theoretical+Study+to+Determine+the+Mechanism+of+Lithium+Carbenoid-Promoted+Cyclopropanation+Reactions+in+Aggregation+and+Solvation+Statesen_HK
dc.identifier.emailPhillips, DL:phillips@hku.hken_HK
dc.identifier.authorityPhillips, DL=rp00770en_HK
dc.description.naturelink_to_subscribed_fulltext-
dc.identifier.doi10.1021/jo062129ien_HK
dc.identifier.pmid17253804-
dc.identifier.scopuseid_2-s2.0-33846918665en_HK
dc.identifier.hkuros131935en_HK
dc.relation.referenceshttp://www.scopus.com/mlt/select.url?eid=2-s2.0-33846918665&selection=ref&src=s&origin=recordpageen_HK
dc.identifier.volume72en_HK
dc.identifier.issue3en_HK
dc.identifier.spage848en_HK
dc.identifier.epage860en_HK
dc.identifier.isiWOS:000243735500022-
dc.publisher.placeUnited Statesen_HK
dc.identifier.scopusauthoridKe, Z=14048262500en_HK
dc.identifier.scopusauthoridZhao, C=7403563836en_HK
dc.identifier.scopusauthoridPhillips, DL=7404519365en_HK

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