Journalartikel

Jahr der Veröffentlichung: 2002

Seiten: 10718-10727

Zeitschrift: Journal of the American Chemical Society

Bandnummer: 124

Heftnummer: 36

ISSN: 0002-7863

DOI Link: https://doi.org/10.1021/ja0265512

Verlag: American Chemical Society

Abstract: 
The mechanisms for the reactions of isobutane and adamantane with polyhalogen electrophiles (HHal(2)(+), Hal(3)(+), Hal(5)(+), and Hal(7)(+), Hal=Cl, Br, or I) were studied computationally at the MP2 and B3LYP levels of theory with the 6-31G** (C, H, Cl, Br) and 3-21G* (I) basis sets, as well as experimentally for adamantane halogenations in Br-2, Br-2/HBr, and I+Cl-/CCl4. The transition structures for the activation step display almost linear C...H...Hal interactions and are characterized by significant charge transfer to the electrophile; the hydrocarbon moieties resemble the respective radical cation structures. The regiospecificities for polar halogenations of the 3degrees C-H bonds of adamantane, the high experimental kinetic isotope effects (k(H)/k(D)=3-4), the rate accelerations in the presence of Lewis and proton (HBr) acids, and the high kinetic orders for halogen (7.5 for Br-2) can only be understood in terms of an H-coupled electron-transfer mechanism. The three centered-two electron (3c-2e) electrophilic mechanistic concept based on the attack of the electrophile on a C-H bond does not apply; electrophilic 3c-2e interactions dominate the C-H activations only with nonoxidizing electrophiles such as carbocations. This was shown by a comparative computational analysis of the electrophilic and H-coupled electron-transfer activation mechanisms for the isobutane reaction with an ambident electrophile, the allyl cation, at the above levels of theory.

Harvard-Zitierstil: Fokin, A., Shubina, T., Gunchenko, P., Isaev, S., Yurchenko, A. and Schreiner, P. (2002) H-coupled electron transfer in alkane C-H Activations with halogen electrophiles, Journal of the American Chemical Society, 124(36), pp. 10718-10727. https://doi.org/10.1021/ja0265512

APA-Zitierstil: Fokin, A., Shubina, T., Gunchenko, P., Isaev, S., Yurchenko, A., & Schreiner, P. (2002). H-coupled electron transfer in alkane C-H Activations with halogen electrophiles. Journal of the American Chemical Society. 124(36), 10718-10727. https://doi.org/10.1021/ja0265512