Himanshu Bhatia, a doctoral candidate in chemistry, will defend their dissertation titled “Synthesis of First-Row Transition Metal Complexes Supported by Tetraaza and Tetraamido Macrocyclic Ligands: Catalysts in Nitrene Transfer Chemistry.” Their advisor, Dr. Pericles Stavropoulos is an  professor in chemistry. The dissertation abstract is provided below.

The development of efficient and sustainable catalysts for nitrene transfer reactions remains an important objective in synthetic chemistry because these transformations provide direct access to valuable nitrogen-containing compounds through C–N bond formation. In particular, the aziridination of olefins offers a versatile route to strained nitrogen heterocycles that serve as important intermediates in pharmaceutical, agrochemical, and materials synthesis. This
dissertation investigates the role of macrocyclic ligand architecture in controlling first-row transition-metal-mediated nitrene transfer through two complementary catalyst platforms: pyridinophane-supported metal complexes and chiral tetraamido macrocyclic cobalt complexes.
In the first study, a 12-membered pyridinophane ligand containing two pyridine and two tertiary amine donors (tBuN4) was employed to support a series of first-row transition-metal complexes, including Mn(II), Fe(II), Co(II), Ni(II), Cu(I), and Cu(II) derivatives. These complexes were evaluated as catalysts for the aziridination of olefins using iminoiodinane nitrene precursors. Among the metals examined, the Cu(I) and Cu(II) complexes displayed the highest catalytic activity, affording efficient aziridination of styrenyl substrates, whereas the Mn, Fe, Co, and Ni analogues exhibited only modest reactivity. Aromatic olefins proved significantly more reactive than aliphatic substrates, while increasing steric congestion at the α- and β-positions reduced product yields and promoted competing ring-opening pathways. Mechanistic investigations, including Hammett analyses, kinetic isotope effect measurements, and stereochemical probe
studies, support a stepwise aziridination pathway involving sequential formation of the two N–C bonds. Computational studies indicate that the reactive copper nitrene intermediates derived from both Cu(I) and Cu(II) possess significant nitrene-centered radical character and closely spaced
spin states, with the greater electrophilicity of the Cu(I)-derived nitrene accounting for its enhanced catalytic performance. The second study focuses on the development of a new family of chiral tetraamido macrocyclic ligands and their corresponding Co(III) complexes as catalysts for nitrene transfer. These complexes are paramagnetic (S = 1) in solution and exhibit semi-reversible Co(II/III) redox processes together with irreversible anodic oxidation events. Evaluation of these cobalt
complexes in reactions of olefins with iminoiodinane nitrene precursors revealed efficient aziridination and allylic amination reactivity, particularly for sterically unhindered styrenes. Mechanistic studies indicate that aziridination proceeds through stepwise formation of the two N–C bonds and involves both polar and radical contributions to the reaction pathway. This behavior differs from that reported for related Co(TAML) systems, in which ligand-centered redox activity and substrate-to-ligand electron transfer play a dominant role. Electrospray
ionization mass spectrometry provides evidence for the formation of both mono- and bis-nitrene cobalt species under catalytic conditions, although their precise electronic structures and roles in the catalytic cycle remain subjects for future investigation. Collectively, these studies demonstrate that macrocyclic ligand design exerts a profound influence on the reactivity and mechanism of first-row transition-metal nitrene-transfer catalysts. The pyridinophane platform reveals the critical role of metal identity in determining catalytic efficiency, while the chiral tetraamido framework illustrates how modification of the ligand
environment can alter the electronic structure and mechanistic behavior of cobalt-mediated nitrene transfer. Together, the results provide new insight into the factors governing C–N bond formation and establish guiding principles for the future development of selective and
sustainable catalysts for aziridination and related nitrene-transfer transformations.