Iron carbide-catalyzed deoxygenative coupling of benzyl alcohols toward bibenzyls under hydrogen atmosphere

doi:10.1016/S1872-2067(24)60256-1

Abstract

Abstract:

The direct deoxygenative homo-coupling of benzyl alcohols holds great promise to build up bibenzyl motifs in organic synthesis, yet it remains a grand challenge in selectivity and activity control. Herein, we first discovered that iron carbide catalysts displayed high efficiency and selectivity in the catalytic deoxygenative homo-coupling of benzyl alcohols into bibenzyls using H₂ as the reductant. Ir-promoted Fe⁰@Fe₅C₂ gave the best performance among the investigated catalysts, and a broad scope of substrates with diverse functional groups could be smoothly converted into bibenzyls, with the yield up to 85%. In addition, in the presence of alkenes, three-component coupling reactions between alcohols and alkenes were also for the first time achieved to construct more complex multi-ring molecules. The radical-trapping experiment and FTIR measurements revealed the radical nature of the reaction and the significantly promoted C-O bond activation after carbonization, respectively. This work will provide guidelines for the rational design of efficient and selective catalysts for the alcohol-involved carbon-carbon coupling reactions.

Key words: Deoxygenative coupling reaction, Benzyl alcohols, Bibenzyls, Iron carbide, Hydrogen atmosphere

Yichao Wang, Leilei Zhang, Xiaoli Pan, Aiqin Wang, Tao Zhang. Iron carbide-catalyzed deoxygenative coupling of benzyl alcohols toward bibenzyls under hydrogen atmosphere[J]. Chinese Journal of Catalysis, 2025, 71: 179-186.

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URL: https://www.cjcatal.com/EN/10.1016/S1872-2067(24)60256-1

https://www.cjcatal.com/EN/Y2025/V71/I4/179

Figures/Tables 8

Scheme 1. Applications (a), typical synthetic methods of bibenzyl (b), and the methodology developed in this work (c).

Fig. 1. Catalyst screening for the deoxygenative coupling of benzyl alcohol toward bibenzyl. Reaction conditions: 2.5 mmol benzyl alcohol, 120 mg catalyst (mass based on Fe2O3), 8 mL n-hexane, 0.6 MPa H2, 220 °C, 12 h, 500 r min-1, dodecane was added as internal standard. ^Trimer: 1,2,3- triphenylpropane. *The carbonization time was lengthened to 8 h. &240 mg Fe2O3.

Scheme 2. The substrate replacement experiments. Reaction conditions: 2.5 mmol benzyl alcohol, 120 mg catalyst (mass based on Ir0.1/Fe2O3), 8 mL n-hexane, 0.6 MPa gas, 220 °C, 12 h, 500 r min-1.

Scheme 3. The substrate scope of deoxygenative coupling of various benzyl alcohols catalyzed by Ir0.1/Fe0@Fe5C2. Reaction conditions: 2 mmol benzyl alcohol, 120 mg catalyst (mass based on Ir0.1/Fe2O3), 8 mL THF, 0.5 MPa H2, 220 °C, 12 h, 400 r min-1, dodecane was added as internal standard. Isolated yields were given. *GC yields.

Scheme 4. Three-component coupling reactions between benzyl alcohols and alkenes. Reaction conditions: 4 mmol benzyl alcohol, 1 mmol alkene, 120 mg Ir0.1/Fe0@Fe5C2, 8 mL n-hexane, 0.4 MPa H2, 220 °C, 12 h, 400 r min-1. Isolated yields were given. *GC yields.

Fig. 2. (a) XRD patterns in different stages during the preparation process of the Ir0.1/Fe0@Fe5C2 catalyst. (b) The AC-HAADF-STEM image of Ir0.1/Fe0@Fe5C2. In situ 57Fe M?ssbauer spectra of Ir0.1/Fe0@Fe5C2 (c) and Fe0@Fe5C2 (d) catalysts and the corresponding fitting results (e). (f) Fe 3d XPS spectra of Fe0@Fe5C2 and Ir0.1/Fe0@Fe5C2 [22] catalysts.

Fig. 3. (a) Radical-trapping experiment. (b) FTIR spectra of benzyl alcohol adsorption on different iron catalysts.

Fig. 4. The proposed reaction mechanism.

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