skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


Title: Site-Selective, Catalyst-Controlled Alkene Aziridination
Transition-metal-catalyzed nitrene transfer is a convenient method to introduce nitrogen into simple substrates through either alkene aziridination or C–H bond amination. Silver complexes have an unusual capability to accommodate a broad range of N-donor ligands and coordination geometries in catalysts competent for nitrene transfer. This behavior has resulted in the ability to achieve tunable chemoselectivity between aziridination and C–H bond amidation, as well as tunable site-selective functionalization between two different C–H bonds. In this paper, efforts to engage the diversity of silver and rhodium catalysts to accomplish selective and tunable aziridination of mixtures of alkenes are discussed. It was found that the selectivity of dinuclear Rh catalysts is dictated largely by steric effects, while the identity of the ligand on silver can be tuned to influence whether the steric or electronic features in the competing alkenes is the primary factor controlling which precursor is preferentially aziridinated.  more » « less
Award ID(s):
1664374
PAR ID:
10095621
Author(s) / Creator(s):
;
Date Published:
Journal Name:
Synthesis
Volume:
50
Issue:
22
ISSN:
0039-7881
Page Range / eLocation ID:
4462 to 4470
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; (, Synlett)
    null (Ed.)
    Nitrene transfer (NT) is a convenient strategy to directly transform C–H bonds into more valuable C–N bonds and exciting advances have been made to improve selectivity. Our work in silver-based NT has shown the unique ability of this metal to enable tunable chemo-, site-, and stereoselective reactions using simple N-dentate ligand scaffolds. Manipulation of the coordination environment and noncovalent interactions around the silver center furnish unprecedented catalyst control in selective NT and provide insights for further improvements in the field. 1 Introduction 1.1 Strategies for Nitrene Transfer 1.2 Brief Summary of Chemocatalyzed Nitrene Transfer 1.3 Focus of this Account 2 Challenges in Chemocatalyzed Nitrene Transfer 2.1 Reactivity Challenges 2.2 Selectivity Challenges 2.3 Chemoselective Nitrene Transfer 2.4 Site-Selective Nitrene Transfer 2.5 Enantioselective Nitrene Transfer 3 Summary and Perspective 3.1 Future Opportunities and Challenges 3.2 Conclusion 
    more » « less
  2. ; ; ; ; ; ; ; ; ; (, Chemical Science)
    Despite the myriad Cu-catalyzed nitrene transfer methodologies to form new C–N bonds (e.g.,amination, aziridination), the critical reaction intermediates have largely eluded direct characterization due to their inherent reactivity. Herein, we report the synthesis of dipyrrin-supported Cu nitrenoid adducts, investigate their spectroscopic features, and probe their nitrene transfer chemistry through detailed mechanistic analyses. Treatment of the dipyrrin CuI complexes with substituted organoazides affords terminally ligated organoazide adducts with minimal activation of the azide unit as evidenced by vibrational spectroscopy and single crystal X-ray diffraction. The Cu nitrenoid, with an electronic structure most consistent with a triplet nitrene adduct of CuI, is accessed following geometric rearrangement of the azide adduct from k1-N terminal ligation to k1-N internal ligation with subsequent expulsion of N2. For perfluorinated arylazides, stoichiometric and catalytic C–H amination and aziridination was observed. Mechanistic analysis employing substrate competition reveals an enthalpically-controlled, electrophilic nitrene transfer for primary and secondary C–H bonds. Kinetic analyses for catalytic amination using tetrahydrofuran as a model substrate reveal pseudo-first order kineticsunderrelevantaminationconditionswithafirst-orderdependenceonbothCuandorganoazide. Activation parameters determined from Eyring analysis(DH‡=9.2(2)kcalmol−1,DS‡=−42(2)calmol−1 K−1, DG‡ 298K =21.7(2) kcal mol−1) and parallel kinetic isotope effect measurements (1.10(2)) are consistent with rate-limiting Cu nitrenoid formation, followed by a proposed stepwise hydrogen-atom abstraction and rapid radical recombination to furnish the resulting C–N bond. The proposed mechanism and experimental analysis are further corroborated by density functional theory calculations. Multiconfigurational calculations provide insight into the electronic structure of the catalytically relevant Cu nitrene intermediates. The findings presented herein will assist in the development of future methodology for Cu-mediated C–N bond forming catalysis. 
    more » « less
  3. ; ; ; ; ; ; ; ; ; (, Chemical Science)
    A dipyrrin-supported copper complex mediates C–H bond amination and aziridination of exogenous substrates using electron-deficient arylazides, proceeding through copper-nitrene adducts. 
    more » « less
  4. ; ; ; (, Chemical Science)
    Rational ligand design in a silver catalyst enables highly selective amination of electron-deficient heterobenzylic C–H bondsvianitrene transfer, with scaffold rigidity crucial for unlocking this elusive reactivity in heteroaromatic compounds. 
    more » « less
  5. ; ; ; (, ChemSusChem)
    Abstract Transition metal‐catalyzed, non‐enzymatic nitrene transfer (NT) reactions to selectively transform C−H and C=C bonds to new C−N bonds are a powerful strategy to streamline the preparation of valuable amine building blocks. However, many catalysts for these reactions use environmentally unfriendly solvents that include dichloromethane, chloroform, 1,2‐dichloroethane and benzene. We developed a high‐throughput experimentation (HTE) protocol for heterogeneous NT reaction mixtures to enable rapid screening of a broad range of solvents for this chemistry. Coupled with the American Chemical Society Pharmaceutical Roundtable (ACSPR) solvent tool, we identified several attractive replacements for chlorinated solvents. Selected catalysts for NT were compared and contrasted using our HTE protocol, including silver supported byN‐dentate ligands, dinuclear Rh complexes and Fe/Mn phthalocyanine catalysts. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email