Reaction channels of iron-oxo and iron-imido molecular intermediates

Non-heme Fe(IV)-oxo intermediates are integral components of many enzymatic and homogeneous catalytic cycles, where they serve as key oxidants that enable challenging transformations. Numerous studies have focused on developing biomimetic non-heme Fe(IV)-oxo catalysts, elucidating their electronic structures, and understanding the nature of their reactivity. Their high-valent nature endows them with the capacity to perform demanding oxidative transformations, as evidenced by their broad application in C-H activation and alkene epoxidation chemistry. The isoelectronic Fe(IV)-imido analogue is much less studied, presenting significant opportunities for catalyst development in nitrene-transfer chemistry, including C-H amination and alkene aziridination. Mechanistically, nitrene transfer involves an Fe-imido intermediate featuring an N-centered radical. Two competing pathways have been described: a σ-channel and a π-channel, defined by whether the radical character is localized in a σ* or π* orbital. Similar to Fe(IV)-oxo chemistry, the reaction channel preference among Fe(IV)-imido catalysts plays a crucial role in determining their reactivities and selectivities. Herein, the nitrene transfer pathways for these species within both reaction channels are explored and comparative examples between Fe(IV)-oxo and Fe(IV)-imido catalysts are discussed.