کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
1322200 | 1499867 | 2015 | 8 صفحه PDF | دانلود رایگان |
• N/O-functionalized N-heterocyclic carbine ligands.
• Bifunctional catalysts.
• Base-free Michael addition reaction.
• Catalytic cycle.
• DFT studies.
A proposed catalytic pathway for a base-free Michael addition reaction mediated by a N/O-functionalized N-heterocyclic carbene (NHC) based bifunctional nickel precatalyst has been probed using density functional theory (DFT) studies. In particular, the base-free Michael addition of a β-dicarbonyl compound namely, 2-acetyl-cyclopentanone (a) with methyl vinyl ketone (b) as catalyzed by a representative bifunctional nickel precatalyst viz. [1-(Me)-3-N-(methylacetamido)imidazol-2-ylidene]2Ni (A) has been investigated. The modeling studies reveal that the nucleophilic attack of a metal bound enolate moiety of a 1,3-dicarbonyl adduct species (B) to the approaching activated olefinic substrate, methyl vinyl ketone (b), is the crucial rate-limiting step of the reaction yielding a Michael addition product adduct species (C). Interestingly, the subsequent intramolecular rearrangement of (C) to a different O-bound intermediate (D) exhibit nearly equal activation barrier.
The mechanistic pathway of a base-free Michael addition reaction catalyzed by a series of bifunctional nickel N-heterocyclic carbene complexes, as probed using computational studies, suggests a nucleophilic attack of a metal bound enolate moiety to an activated olefin substrate to be a crucial rate-limiting step of the reaction.Figure optionsDownload as PowerPoint slide
Journal: Journal of Organometallic Chemistry - Volume 775, 1 January 2015, Pages 109–116