Graduate Research
My dissertation research involves the design and development of transition metal-catalyzed C–H bond amination reactions that use azides as the source of the nitrogen-atom. These studies have enabled the preparation of a wide variety of fundamental aromatic N-heterocyclic compounds by unexpected mechanisms, some of which we have elucidated.
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The prospect of direct functionalization of C-H bonds has driven the development of chemoselective synthetic methods that obviate pre-functionalization, thereby improving synthetic efficiency. Transition metals are among the best mediators of direct functionalization when used catalytically and without additives. There are two general classes of direct transition-metal catalyzed C-H bond amination reactions, but both require stoichiometric oxidants.
1) In palladium-catalyzed C-H activation/nitrene insertion reactions, a reactive metal complex activates a C-H bond which then incorporates an in situ-generated nitrene, followed by directing group-assisted liberation of catalyst.
2) The second general type of direct C-H bond amination involves rhodium nitrenoid C-H bond insertion. This method requires stoichiometric oxidants to generate a metallolabile iminoiodinane amenable to the formation of a rhodium nitrenoid, which inserts into an adjacent C-H bond.
The conditions for rhodium nitrenoid insertion contrast sharply with analogous rhodium carbenoid insertion reactions developed over the past two decades. As shown above, rhodium nitrenoid insertion requires stoichiometric organic and inorganic oxidants, which produce iodobenzene and acetic acid by-products. On the other hand, Rh2(II)-catalyzed carbene insertion reactions use diazo compounds to generate carbenes, producing nitrogen gas as the only by-product without any additives.
Under the premise of developing benign and efficient C-H bond amination reactions on par with transition metal-catalyzed carbene insertion conditions, my graduate research has attempted to narrow the gap between metallocarbene-and metallonitrene-based C-H functional reactions.
