A Versatile Tripodal Cu(I) Reagent for C–N Bond Construction via Nitrene-Transfer Chemistry: Catalytic Perspectives and Mechanistic Insights on C–H Aminations/Amidinations and Olefin Aziridinations
| Autor: | Yiannis Sanakis, Thomas R. Cundari, Qiuwen Wang, Daniel B. Pardue, Lingyu Chi, George Mitrikas, Vivek Bagchi, Patrina Paraskevopoulou, Leroy Cronin, Jennifer S. Mathieson, Amitava Choudhury, Purak Das, Pericles Stavropoulos |
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| Rok vydání: | 2014 |
| Předmět: | |
| Zdroj: | Journal of the American Chemical Society. 136:11362-11381 |
| ISSN: | 1520-5126 0002-7863 |
| DOI: | 10.1021/ja503869j |
| Popis: | A Cu(I) catalyst (1), supported by a framework of strongly basic guanidinato moieties, mediates nitrene-transfer from PhI═NR sources to a wide variety of aliphatic hydrocarbons (C-H amination or amidination in the presence of nitriles) and olefins (aziridination). Product profiles are consistent with a stepwise rather than concerted C-N bond formation. Mechanistic investigations with the aid of Hammett plots, kinetic isotope effects, labeled stereochemical probes, and radical traps and clocks allow us to conclude that carboradical intermediates play a major role and are generated by hydrogen-atom abstraction from substrate C-H bonds or initial nitrene-addition to one of the olefinic carbons. Subsequent processes include solvent-caged radical recombination to afford the major amination and aziridination products but also one-electron oxidation of diffusively free carboradicals to generate amidination products due to carbocation participation. Analyses of metal- and ligand-centered events by variable temperature electrospray mass spectrometry, cyclic voltammetry, and electron paramagnetic resonance spectroscopy, coupled with computational studies, indicate that an active, but still elusive, copper-nitrene (S = 1) intermediate initially abstracts a hydrogen atom from, or adds nitrene to, C-H and C═C bonds, respectively, followed by a spin flip and radical rebound to afford intra- and intermolecular C-N containing products. |
| Databáze: | OpenAIRE |
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