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Volumn 27, Issue 13, 2008, Pages 3153-3160

Catalytic annulation of heterocycles via a novel redox process involving the imidazolium salt N-heterocyclic carbene couple

Author keywords

[No Author keywords available]

Indexed keywords

ALKYLATION; CATALYSIS; IONIZATION OF LIQUIDS; NICKEL; NICKEL ALLOYS; NITROGEN COMPOUNDS; SALTS;

EID: 47949114467     PISSN: 02767333     EISSN: None     Source Type: Journal    
DOI: 10.1021/om800140n     Document Type: Article
Times cited : (64)

References (83)
  • 69
    • 47949121763 scopus 로고    scopus 로고
    • Some salts are extremely hygroscopic, which precluded satisfactory elemental analysis
    • Some salts are extremely hygroscopic, which precluded satisfactory elemental analysis.
  • 70
    • 47949103604 scopus 로고    scopus 로고
    • Arrows indicate carbon atoms at which hydride insertion occurred
    • Arrows indicate carbon atoms at which hydride insertion occurred.
  • 72
    • 47949122794 scopus 로고    scopus 로고
    • The fate of Br- during the course of the reaction (i.e. bound to Ni or in the second sphere of coordination) is not known exactly; therefore, we have voluntarily left it out of the formula. Also, a reviewer has suggested an alternative view on our proposed mechanism. It was pointed out that after the oxidative addition a nickel dicarbene complex is formed, consisting of the original carbene ligand and the carbene generated from the substrate imidazolium salt. The substrate now becomes a chelate ligand (carbene, η2 coordination) and may provide a better ligand than the original IMes monodentate carbene ligand. In this case both carbene ligands would compete for coordination at the metal center. Therefore, the suggestion is that the original IMes ligand is eliminated as the imidazolium salt IMesHBr, and afterwards the catalytic cycle takes place with the chelating carbene as the actual ligand L. However, we feel that our previous studies46,51 provide a sound ba
    • 46,51 provide a sound basis for the mechanism depicted in Scheme 3. Indeed, dissociation of IMes or reductive elimination of IMesHBr is unlikely to be a favorable process, considering (a) the strong Ni-NHC BDE and (b) the very exothermic C-H oxidative addition reaction of Ni(0) to imidazolium salts. We agree that a chelating NHC-olefin ligand would form very stable species; however, we think it would not be kinetically possible.
  • 73
    • 47949089700 scopus 로고    scopus 로고
    • The last step of the catalytic cycle in the intermolecular version of this reaction is thought to proceed from a 14-electron Ni(II) species (see ref 46 for a detailed discussion, which facilitates reductive elimination. The coordination of an extra olefin might inhibit this step, by creating a stabilized 16-electron Ni(II) complex. Indeed, we observed a green coloration appearing in the course of the reaction at low loadings, indicating a Ni(II) species
    • The last step of the catalytic cycle in the intermolecular version of this reaction is thought to proceed from a 14-electron Ni(II) species (see ref 46 for a detailed discussion), which facilitates reductive elimination. The coordination of an extra olefin might inhibit this step, by creating a stabilized 16-electron Ni(II) complex. Indeed, we observed a green coloration appearing in the course of the reaction at low loadings, indicating a Ni(II) species.


* 이 정보는 Elsevier사의 SCOPUS DB에서 KISTI가 분석하여 추출한 것입니다.