‘Carbene Radicals’ in CoII(por)-Catalyzed Olefin Cyclopropanation
作者： Wojciech I. Dzik , Xue Xu , X. Peter Zhang , Joost N. H. Reek , Bas de Bruin
DOI: 10.1021/JA103768R
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摘要: The mechanism of cobalt(II)−porphyrin-mediated cyclopropanation olefins with diazoesters was studied. first step—reaction cobalt(II)−porphyrin ethyl diazoacetate (EDA)—was examined using EPR and ESI-MS techniques. EDA reacts to form a 1:1 Co(por)(CHCOOEt) adduct that exists as two isomers: the ‘bridging carbene’ C′ in which ‘carbene’ is bound metal pyrrolic nitrogen porphyrin has d7 configuration on metal, ‘terminal C behaves redox noninnocent ligand having d6 cobalt center unpaired electron residing carbon atom. subsequent reactivities thus formed ‘cobalt carbene radical’ propene, styrene, methyl acrylate were studied DFT calculations. calculations suggest formation rate-limiting step for unfunctionalized CoII(por) cyclopropane ring proceeds via stepwise radical proces...
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