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

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.