A Versatile Tripodal Cu(I) Reagent for C鈥揘 Bond Construction via Nitrene-Transfer Chemistry: Catalytic Perspectives and Mechanistic Insights on C鈥揌 Aminations/Amidinations and Olefin Aziridinations
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- 作者：Vivek Bagchi ; Patrina Paraskevopoulou ; Purak Das ; Lingyu Chi ; Qiuwen Wang ; Amitava Choudhury ; Jennifer S. Mathieson ; Leroy Cronin ; Daniel B. Pardue ; Thomas R. Cundari ; George Mitrikas ; Yiannis Sanakis ; Pericles Stavropoulos
- 刊名：Journal of the American Chemical Society
- 出版年：2014
- 出版时间：August 13, 2014
- 年：2014
- 卷：136
- 期：32
- 页码：11362-11381
- 全文大小：1132K
- ISSN：1520-5126
文摘
A CuI catalyst (1), supported by a framework of strongly basic guanidinato moieties, mediates nitrene-transfer from PhI鈺怤R sources to a wide variety of aliphatic hydrocarbons (C鈥揌 amination or amidination in the presence of nitriles) and olefins (aziridination). Product profiles are consistent with a stepwise rather than concerted C鈥揘 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鈥揌 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鈥揌 and C鈺怌 bonds, respectively, followed by a spin flip and radical rebound to afford intra- and intermolecular C鈥揘 containing products.