Journal
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
Volume 135, Issue 4, Pages 1456-1462Publisher
AMER CHEMICAL SOC
DOI: 10.1021/ja309873z
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Funding
- National Science Foundation [CHE-0548209]
- NSF [OCI-1053575]
- Direct For Mathematical & Physical Scien [1059084] Funding Source: National Science Foundation
- Division Of Chemistry [1059084] Funding Source: National Science Foundation
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The mechanism and origins of selectivities in [Ni(NHC)]-catalyzed intramolecular (5 + 2) cycloadditions and homo-ene reactions of vinylcyclopropanes (VCPs) and alkynes have been studied using density functional theory. The preferred mechanism involves oxidative alkyne-alkene cyclization to form a metallacyclopentene intermediate, in contrast to a cyclopropane cleavage pathway in the reaction with Rh(I) catalysts. The selectivity between the (5 + 2) and homo-ene products is determined in the subsequent competing reductive elimination and beta-hydride elimination steps. Two similar-sized N-heterocyclic carbene (NHC) ligands, SIPr and ItBu, yielded reversed product selectivity, favoring the (5 + 2) and homo-ene products respectively. This is attributed to the anisotropic steric environment of these NHC ligands, which positions the bulky substituents on the ligand toward different directions and leads to distinct steric control in the reductive elimination and beta-hydride elimination transition states.
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