Precise regulation of the electronic states of catalytic sites through molecular engineering is highly desired to boost catalytic performance. Herein, a facile strategy was developed to synthesize efficient oxygen reduction reaction (ORR) catalysts, based on mononuclear iron phthalocyanine supported on commercially available multi‐walled carbon nanotubes that contain electron‐donating functional groups (FePc/CNT‐R, with “R” being −NH2, −OH, or −COOH). These functional groups acted as axial ligands that coordinated to the Fe site, confirmed by X‐ray photoelectron spectroscopy and synchrotron‐radiation‐based X‐ray absorption fine structure. Experimental results showed that FePc/CNT‐NH2, with the most electron‐donating −NH2 axial ligand, exhibited the highest ORR activity with a positive onset potential (Eonset=1.0 V vs. reversible hydrogen electrode) and half‐wave potential (E1/2=0.92 V). This was better than the state‐of‐the‐art Pt/C catalyst (Eonset=1.00 V and E1/2=0.85 V) under the same conditions. Overall, the functionalized FePc/CNT‐R assemblies showed enhanced ORR performance in comparison to the non‐functionalized FePc/CNT assembly. The origin of this behavior was investigated using density functional theory calculations, which demonstrated that the coordination of electron‐donating groups to FePc facilitated the adsorption and activation of oxygen. This study not only demonstrates a series of advanced ORR electrocatalysts, but also introduces a feasible strategy for the rational design of highly active electrocatalysts for other proton‐coupled electron transfer reactions.

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Transition metal radical‐type carbene transfer catalysis is a sustainable and atom‐efficient method to generate C−C bonds, especially to produce fine chemicals and pharmaceuticals. A significant amount of research has therefore been devoted to applying this methodology, which resulted in innovative routes toward otherwise synthetically challenging products and a detailed mechanistic understanding of the catalytic systems. Furthermore, combined experimental and theoretical efforts elucidated the reactivity of carbene radical complexes and their off‐cycle pathways. The latter can imply the formation of N‐enolate and bridging carbenes, and undesired hydrogen atom transfer by the carbene radical species from the reaction medium which can lead to catalyst deactivation. In this concept paper, we demonstrate that understanding off‐cycle and deactivation pathways not only affords solutions to circumvent them, but can also uncover novel reactivity for new applications. In particular, considering off‐cycle species involved in metalloradical catalysis can stimulate further development of radical‐type carbene transfer reactions.

Enabling (radical-type) nitrene transfer reactions in water can open up a wide range of (novel) applications, such as the in vivo synthesis of medicines. However, these reactions typically suffer from oxygen-containing side-product formation, of which the origin is not fully understood. Therefore, we investigated aqueous styrene aziridination using a water-soluble [CoIII(TAMLred)]– catalyst known to be active in radical-type nitrene transfer in organic solvents. The cobalt-catalyzed aziridination of styrene in water (pH = 7) yielded styrene oxide as the major product, next to minor amounts of aziridine product. Based on 18O-labeling studies, catalysis and mass spectrometry experiments, we demonstrated that styrene oxide formation proceeds via hydrolysis of the formed nitrene radical complexes. Computational studies support that this process is facile and yields oxyl radical complexes active in oxygen atom transfer to styrene. Based on these mechanistic insights, the pH was adjusted to afford selective aziridination in water.