Nitrene Photochemistry of Manganese N‐Haloamides Van Trieste, Gerard P.; Reid, Kaleb A.; Hicks, Madeline H. ...
Angewandte Chemie (International ed.),
December 13, 2021, Letnik:
60, Številka:
51
Journal Article
Recenzirano
Odprti dostop
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 MnIII N‐haloamide complexes. The S=2 N‐haloamide complexes are characterized by 1H 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 MnII and amidyl radical intermediates; in contrast, photolysis of N‐iodoamides proceeds via N−I cleavage to generate a MnIV 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.
Here we report the synthesis and nitrene transfer photochemistry of MnIII 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 MnII and amidyl radical species; in contrast, photolysis of N‐iodoamides proceeds via N−I cleavage yielding a formally MnIV nitrenoid.
Four-coordinate transition-metal complexes can adopt a diverse array of coordination geometries, with square planar and tetrahedral coordination being the most prevalent. Previously, we reported the ...synthesis of a trinuclear Fe(II) complex, Fe 3 TPM 2 , supported by a 3-fold-symmetric 2-pyridylpyrrolide ligand i.e., tris(5-(pyridin-2-yl)-1H-pyrrol-2-yl)methane that featured a rare cis-divacant octahedral (CDO) geometry at each Fe(II) center. Here, a series of truncated 2-pyridylpyrrolide ligands are described that support mono- and binuclear Fe(II) complexes that also exhibit CDO geometries. Metalation of the tetradentate ligand bis5-(pyridin-2-yl)-1H-pyrrol-2-ylmethane (H 2 BPM) in tetrahydrofuran (THF) results in the binuclear complex Fe 2 (BPM) 2 (THF) 2 in which both Fe(II) ions are octahedrally coordinated. The coordinated THF solvent ligands are labile: THF dissociation leads to Fe 2 (BPM) 2 , which features five-coordinate Fe(II) ions. The Fe–Fe distance in these binuclear complexes can be elongated by ligand methylation. Metalation of bis5-(6-methylpyridin-2-yl)-1H-pyrrol-2-ylmethane (H 2 BPM Me ) in THF leads to the formation of four-coordinate, CDO Fe(II) centers in Fe(BPM Me ) 2 . Further ligand truncation affords bidentate ligands 2-(1H-pyrrol-2-yl)pyridine (PyrPyrrH) and 2-methyl-6-(1H-pyrrol-2-yl)pyridine (Pyr Me PyrrH). Metalation of these ligands in THF affords six-coordinate complexes Fe(PyrPyrr) 2 (THF) 2 and Fe(Pyr Me Pyrr) 2 (THF) 2 . Dissociation of labile solvent ligands provides access to four-coordinate Fe(II) complexes. Ligand disproportionation at Fe(PyrPyrr) 2 results in the formation of Fe(PyrPyrr) 3 and Fe(0). Ligand methylation suppresses this disproportionation and enables isolation of Fe(Pyr Me Pyrr) 2 , which is rigorously CDO. Complete ligand truncation, by separating the 2-pyridylpyrrolide ligands into the constituent monodentate pyridyl and pyrrolide donors, affords Fe(Pyr) 2 (Pyrr) 2 in which Fe(II) is tetrahedrally coordinated. Computational analysis indicates that the potential energy surface that dictates the coordination geometry in this family of four-coordinate complexes is fairly flat in the vicinity of CDO coordination. These synthetic studies provide the structural basis to explore the implications of CDO geometry on Fe-catalyzed reactions.
C−H amination and amidation by catalytic nitrene transfer are well‐established and typically proceed via electrophilic attack of nitrenoid intermediates. In contrast, the insertion of (formal) ...terminal nitride ligands into C−H bonds is much less developed and catalytic nitrogen atom transfer remains unknown. We here report the synthesis of a formal terminal nitride complex of palladium. Photocrystallographic, magnetic, and computational characterization support the assignment as an authentic metallonitrene (Pd−N) with a diradical nitrogen ligand that is singly bonded to PdII. Despite the subvalent nitrene character, selective C−H insertion with aldehydes follows nucleophilic selectivity. Transamidation of the benzamide product is enabled by reaction with N3SiMe3. Based on these results, a photocatalytic protocol for aldehyde C−H trimethylsilylamidation was developed that exhibits inverted, nucleophilic selectivity as compared to typical nitrene transfer catalysis. This first example of catalytic C−H nitrogen atom transfer offers facile access to primary amides after deprotection.
Photocatalytic nitrogen atom transfer into aldehyde C−H bonds is reported. A palladium(II) metallonitrene species with nitrogen‐centered biradical character was identified as the key intermediate and was photocrystallographically, magnetically and computationally characterized. The nucleophilic metallonitrene C−H insertion step results in inverted selectivity for the net nitrene transfer catalysis.
C−H amination and amidation by catalytic nitrene transfer are well‐established and typically proceed via electrophilic attack of nitrenoid intermediates. In contrast, the insertion of (formal) ...terminal nitride ligands into C−H bonds is much less developed and catalytic nitrogen atom transfer remains unknown. We here report the synthesis of a formal terminal nitride complex of palladium. Photocrystallographic, magnetic, and computational characterization support the assignment as an authentic metallonitrene (Pd−N) with a diradical nitrogen ligand that is singly bonded to PdII. Despite the subvalent nitrene character, selective C−H insertion with aldehydes follows nucleophilic selectivity. Transamidation of the benzamide product is enabled by reaction with N3SiMe3. Based on these results, a photocatalytic protocol for aldehyde C−H trimethylsilylamidation was developed that exhibits inverted, nucleophilic selectivity as compared to typical nitrene transfer catalysis. This first example of catalytic C−H nitrogen atom transfer offers facile access to primary amides after deprotection.
Photocatalytic nitrogen atom transfer into aldehyde C−H bonds is reported. A palladium(II) metallonitrene species with nitrogen‐centered biradical character was identified as the key intermediate and was photocrystallographically, magnetically and computationally characterized. The nucleophilic metallonitrene C−H insertion step results in inverted selectivity for the net nitrene transfer catalysis.
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 MnIII N‐haloamide complexes. The S=2 N‐haloamide complexes are characterized by 1H 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 MnII and amidyl radical intermediates; in contrast, photolysis of N‐iodoamides proceeds via N−I cleavage to generate a MnIV 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.
Here we report the synthesis and nitrene transfer photochemistry of MnIII 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 MnII and amidyl radical species; in contrast, photolysis of N‐iodoamides proceeds via N−I cleavage yielding a formally MnIV nitrenoid.
Objective. There has been a growing recognition of the need for better pharmacologic management of chronic pain among older adults. To address this need, the National Institutes of Health Pain ...Consortium sponsored an “Expert Panel Discussion on the Pharmacological Management of Chronic Pain in Older Adults” conference in September 2010 to identify research gaps and strategies to address them. Specific emphasis was placed on ascertaining gaps regarding use of opioid and nonsteroidal anti‐inflammatory medications because of continued uncertainties regarding their risks and benefits.
Design. Eighteen panel members provided oral presentations; each was followed by a multidisciplinary panel discussion. Meeting transcripts and panelists' slide presentations were reviewed to identify the gaps and the types of studies and research methods panelists suggested could best address them.
Results. Fifteen gaps were identified in the areas of treatment (e.g., uncertainty regarding the long‐term safety and efficacy of commonly prescribed analgesics), epidemiology (e.g., lack of knowledge regarding the course of common pain syndromes), and implementation (e.g., limited understanding of optimal strategies to translate evidence‐based pain treatments into practice). Analyses of data from electronic health care databases, observational cohort studies, and ongoing cohort studies (augmented with pain and other relevant outcomes measures) were felt to be practical methods for building an age‐appropriate evidence base to improve the pharmacologic management of pain in later life.
Conclusion. Addressing the gaps presented in the current report was judged by the panel to have substantial potential to improve the health and well‐being of older adults with chronic pain.
What is already known about this topic? Multisystem inflammatory syndrome in children (MIS-C) is a rare but serious condition typically occurring 2–6 weeks after SARS-CoV-2 infection and ...characterized by fever and multiorgan involvement. What is added by this report? MIS-C incidence has decreased from early in the COVID-19 pandemic (highest in late 2020–early 2021), but cases continue to occur with a recent relative increase in the fall of 2023 after a period of increased COVID-19 activity in the general population. Among 117 patients with MIS-C in 2023, approximately one half required intensive care unit–level care. More than 80% (92 of 112) of MIS-C cases were in vaccine-eligible but unvaccinated children, and among the 20 vaccinated children, 60% likely had waned immunity at the time of MIS-C illness. What are the implications for public health practice? MIS-C cases continue to occur but at low rates, making ongoing surveillance valuable. COVID-19 vaccination remains important for preventing MIS-C.
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