Key mechanistic insights into the intramolecular C-H bond amination and double bond aziridination in sulfamate esters catalyzed by dirhodium tetracarboxylate complexes

Publication date: Available online 11 December 2017 Source:Journal of Organometallic Chemistry Author(s): Adrián Varela-Álvarez, Brandon E. Haines, Djamaladdin G. Musaev Density Functional Theory was used to study the mechanisms of intramolecular C-H amination and olefin aziridination reactions of a variety of sulfamate esters. Particular emphasis is placed on the mechanism and factors governing amination of primary, secondary, tertiary and benzylic C-H bonds, the competition between tertiary and benzylic C-H amination, and the competition between allylic C-H amination and olefin aziridination. In these studies we used three different dirhodium paddlewheel catalysts, such as model (H2O)Rh2(O2CH)4 (I), (H2O)Rh2(AcO)4 (II), and (H2O)Rh2(esp)2 (III). In general, we found that all catalysts have a diamagnetic closed shell singlet state with a single Rh-Rh σ-bond. Active catalytic species in the studied amination reactions are triplet state dirhodium-nitrene complexes with the Rh–Rh single bond and Rh-N double bond (with one σ-bond and two “one-electron π-bonds”). From the active nitrenoid species, the C-H bond amination proceeds via triplet-to-singlet surface crossing and singlet state concerted C-H insertion mechanism. The calculated energy barriers correlate with the trend in homolytic bond dissociation energy of the activated C-H bonds. With the allylic substrate, the competing C=C double bond aziridination follows a stepwise pathway involving the formation of ...

Source: Journal of Organometallic Chemistry - December 12, 2017 Category: Chemistry Source Type: research