Research ArticleChemistry

Metal-free activation of molecular oxygen by covalent triazine frameworks for selective aerobic oxidation

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Science Advances  03 Apr 2020:
Vol. 6, no. 14, eaaz2310
DOI: 10.1126/sciadv.aaz2310
  • Fig. 1 Synthesis and structural characterization of CTFs synthesized at different temperatures.

    (A) Illustration of the ideal ordered structure of CTF-1. (B) Schematic representation of the possible structure at relatively high temperatures of synthesis (the ratios of nitrogen species of CTFs can be tuned through adjusting the reaction temperature). (C) DRIFT spectra. (D) N 1s XPS spectrum of the CTF-1-400. (E) Nitrogen adsorption isotherms. (F) Powder XRD patterns. (G) TEM image and elemental mapping images of CTF-1-400. (H) Raman spectra. a.u., arbitrary units.

  • Fig. 2 Catalytic performance of CTF-1-400.

    Comparison of the CTF-1-400 catalyst with other N-doped carbon-based metal-free catalysts for aerobic oxidation of benzyl alcohol (48, 50). Reaction conditions for CTF-1-400: 8.5 mg of CTF-1-400 catalyst, 0.33 mmol of substrate, 0.2 mmol of Cs2CO3, 330 μl of toluene, O2 (1 atm), 100°C, 0.75 hour. AC, activated carbon.

  • Fig. 3 Structural characterization of CTFs-1 synthesized at different temperatures.

    (A) Ratios of C/N determined by elemental analyses. (B) N 1s XPS spectrum of the CTF-1-300. (C) N 1s XPS spectrum of the CTF-1-450. (D) N 1s XPS spectrum of the CTF-1-500. (E) N 1s XPS spectrum of the CTF-1-550. (F) N 1s XPS spectrum of the CTF-1-600.

  • Fig. 4 Mechanistic studies.

    (A) Relationship between the conversion of benzyl alcohol and different N species within the CTF-1 materials synthesized at different temperatures [reaction conditions: 17 mg of catalyst, 0.33 mmol of substrate, 0.2 mmol of Cs2CO3, 330 μl of toluene, O2 (1 atm), 100°C, 2 hours]. (B) Effect of base on the EPR spectra of CTF-1-400 in the reaction mixture. (C) For clarification, the EPR spectrum of the CTF-1-400 without DMPO is eliminated from that of the solution containing both the CTF-1 and the spin trap (DMPO). (D) Schematic representation of the proposed reaction mechanism for the oxidation of benzyl alcohol using CTF-1-400 as the metal-free catalyst.

  • Table 1 Results of aerobic oxidation of several alcohols using the CTF-1-400 catalyst.

    Reaction conditions: 17 mg of CTF-1-400 catalyst, 0.33 mmol of substrate, 0.2 mmol of Cs2CO3, 330 μl of toluene, O2 (1 atm), 100°C, 3 hours for 2a–2i and 2p–2r, 12 hours for 2j–2o and 2s–2u. Conversions are an average of at least three runs. Full conversion (99%) was obtained for 2a to 2h after 12 hours. All substrates displayed >99% selectivity toward the corresponding aldehyde/ketone.


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  • Table 2 Various control experiments to obtain insights into the reaction mechanism.

    Reaction conditions: 17 mg of catalyst, 0.33 mmol of benzyl alcohol, 0.2 mmol of Cs2CO3, 330 μl of toluene, O2, 100°C, 2 hours for entries 2 to 7 and 12 hours for entries 1 and 8 to 16, Conversions are an average of at least three runs. n.d., not detected.

    EntryCatalystConversion
    (%)
    Selectivity
    (%)*
    1CTF-HUST-15>99
    2CTF-1-30035>99
    3CTF-1-40064>99
    4CTF-1-45069>99
    5CTF-1-50074>99
    6CTF-1-55087>99
    7CTF-1-60097>99
    8No catalyst<1n.d.
    9CTF-1-40099>99
    10CTF-1-4003>99
    11CTF-1-40011>99
    12§CTF-1-40099>99
    13||CTF-1-40099>99
    14CTF-1-40099>99
    15#CTF-1-40026>99
    16**CTF-1-4007>99

    *Selectivity toward benzaldehyde.

    †Under Ar atmosphere.

    ‡With p-benzoquinone as the superoxide (O2) scavenger.

    §With tert-butyl alcohol as the OH scavenger.

    ||With NaN3 as the 1O2 scavenger.

    ¶With 1,3-diphenylisobenzofuran as the 1O2 scavenger.

    #With ammonium oxalate.

    **The reaction was done at room temperature.

    Supplementary Materials

    • Supplementary Materials

      Metal-free activation of molecular oxygen by covalent triazine frameworks for selective aerobic oxidation

      Sara Abednatanzi, Parviz Gohari Derakhshandeh, Karen Leus, Henk Vrielinck, Freddy Callens, Johannes Schmidt, Aleksandr Savateev, Pascal Van Der Voort

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      • Tables S1 to S7
      • Figs. S1 to S3

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