Carbon doped hexagonal BN as a highly efficient metal-free base catalyst for Knoevenagel condensation reaction

Development of new heterogeneous base catalysts for Knoevenagel condensation reactions is critical for practical applications. Herein, we demonstrate that carbon doped hexagonal boron nitride (BCN) exhibits a high catalytic activity for Knoevenagel condensation of benzaldehyde with malononitrile, producing benzylidene malononitrile under mild reaction conditions. An 81.9% conversion can be achieved over BCN after 15 min reaction time, which is 1.8 times with respect to hexagonal boron nitride (h-BN) and 27 times over C3N4. Moreover, the BCN catalyst could be easily separated and recycled for several runs without obvious deactivation. Experimental results, spectroscopic characterizations, combined with first-principle calculations, suggest the reaction likely follows a dissociative adsorption mechanism on the oxygen terminated BCN edge. The C atoms doping plays a vital role in promoting the desorption of the intermediates. This study can open up a new avenue for the Knoevenagel condensation reaction with metal-free catalysis.