Nitrene Photochemistry of Manganese N‐Haloamides. Issue 51 (16th November 2021)

• Record Type: Journal Article
• Authors: Van Trieste, Gerard P.; Reid, Kaleb A.; Hicks, Madeline H.; Das, Anuvab; Figgins, Matthew T.; Bhuvanesh, Nattamai; Ozarowski, Andrew; Telser, Joshua; Powers, David C.
• Is Part Of: Angewandte Chemie international edition. Volume 60:Issue 51(2021)
• Page Start: 26647
• Page End: 26655
• Publication Date: 2021-11-16
• Subjects: C−H Amination -- Group Transfer Catalysis -- Metal Nitrenes -- Photochemistry -- Reactive Intermediates; Chemistry -- Periodicals; 540
• DOI: 10.1002/anie.202108304
• Languages: English
• ISSNs: 1433-7851

Abstract

Abstract: Manganese complexes supported by macrocyclic tetrapyrrole ligands represent an important platform for nitrene transfer catalysis and have been applied to both C−H amination and olefin aziridination catalysis. The reactivity of the transient high‐valent Mn nitrenoids that mediate these processes renders characterization of these species challenging. Here we report the synthesis and nitrene transfer photochemistry of a family of Mn III N ‐haloamide complexes. The S= 2 N ‐haloamide complexes are characterized by 1 H NMR, UV‐vis, IR, high‐frequency and ‐field EPR (HFEPR) spectroscopies, and single‐crystal X‐ray diffraction. Photolysis of these complexes results in the formal transfer of a nitrene equivalent to both C−H bonds, such as the α‐C−H bonds of tetrahydrofuran, and olefinic substrates, such as styrene, to afford aminated and aziridinated products, respectively. Low‐temperature spectroscopy and analysis of kinetic isotope effects for C−H amination indicate halogen‐dependent photoreactivity: Photolysis of N ‐chloroamides proceeds via initial cleavage of the Mn−N bond to generate Mn II and amidyl radical intermediates; in contrast, photolysis of N ‐iodoamides proceeds via N−I cleavage to generate a Mn IV nitrenoid (i.e., {MnNR} 7 species). These results establish N ‐haloamide ligands as viable precursors in the photosynthesis of metal nitrenes and highlight the power of ligand design to provide access to reactive intermediates in group‐transfer catalysis. Abstract : Here we report the synthesis and nitrene transfer photochemistry of Mn III N ‐haloamide complexes. Photolysis results in both C−H bond amination and olefinic aziridination products. Low‐temperature spectroscopy indicates halogen‐dependent photoreactivity: Photolysis of N ‐chloroamides cleaves the Mn−N bond to generate Mn II and amidyl radical species; in contrast, photolysis of N ‐iodoamides proceeds via N−I cleavage yielding a formally Mn IV nitrenoid.