@article{2928847,
    title = "Comparative Nitrene-Transfer Chemistry to Olefinic Substrates Mediated by a Library of Anionic Mn(II) Triphenylamido-Amine Reagents and M(II) Congeners (M = Fe, Co, Ni) Favoring Aromatic over Aliphatic Alkenes",
    author = "Vivek Bagchi and Anshika Kalra and Purak Das and Patrina Paraskevopoulou and Saidulu Gorla and Lin Ai and Qiuwen Wang and Sudip Mohapatra and Amitava Choudhury and Zhicheng Sun and Thomas R. Cundari and Pericles Stavropoulos",
    journal = "ACS Catalysis",
    year = "2018",
    volume = "8",
    number = "10",
    pages = "9183--9206",
    publisher = "American Chemical Society (ACS)",
    issn = "2155-5435",
    doi = "10.1021/acscatal.8b01941",
    keywords = "manganese; iron; cobalt; trisamido-amine ligands; nitrene-transfer
catalysis; electrochemistry; mechanistic studies; computational studies",
    abstract = "Selective amination of sigma and pi entities such as C-H and C=C bonds
of substrates remains a challenging endeavor for current catalytic
methodologies devoted to the synthesis of abundant nitrogen-containing
chemicals. The present work addresses an approach toward discriminating
aromatic over aliphatic alkenes in aziridination reactions, relying on
the use of anionic metal reagents (M = Mn, Fe, Co, Ni) to attenuate
reactivity in a metal-dependent manner. A family of Mn-II reagents
bearing a triphenylamido-amine scaffold and various pendant arms has
been synthesized and characterized by various techniques, including
cyclic voltammetry. Aziridination of styrene by PhI=NTs in the presence
of each Mn-II catalyst establishes a trend of increasing yield with
increasing Mn-II/III anodic potential. The Fe-II, Co-II, and Ni-II
congeners of the highest-yielding Mn-II catalyst have been synthesized
and explored in the aziridination of aromatic and aliphatic alkenes,
exhibiting good to high yields with para-substituted styrenes, low to
modest yields with sterically congested styrenes, and invariably low
yields with aliphatic olefins. Co-II aziridination in comparison to
Mn-II but is less selective than Mn-II in competitive aziridinations of
nonconjugated olefins. Indeed, Mn-II proved to be highly selective even
versus well-established copper and rhodium aziridination reagents.
Mechanistic investigations and computational studies indicate that all
metals follow a two-step styrene aziridination pathway (successive
formation of two N-C bonds), featuring a turnover-limiting metal-nitrene
addition to an olefinic carbon, followed by product-determining ring
closure. Both steps exhibit activation barriers in the order Fe > Mn >
Co, most likely stemming from relevant metal-nitrene electrophilicities
and M-II/III redox potentials. The aziridination of aliphatic olefins
follows the same stepwise path, albeit with a considerably higher
activation barrier and a weaker driving force for the formation of the
initial N-C bond, succeeded by ring closure with a miniscule barrier."
}