Selective transfer hydrogenation of nitrobenzene to aniline or azobenzene is important for the conversion and utility of nitroarenes. Among the hydrogen sources, isopropanol is a commonly used hydrogen donor. Transition metal-based catalysts are required for these reactions. Possible hydride transfer mechanisms have been elucidated in these catalytic reactions, but studies using metal-free carbon-based catalysts to achieve this reaction are scant.<br/>Recently, our group developed a novel approach which enables fast fabrication of holey graphene nanoplatelets (HGn), which are rich in nanometer sized holes, while being nearly defect-free in their non-hole regions. Interestingly, the edges associated with the nanoholes are dominated by zigzag geometry. It has been theoretically predicted and experimentally observed that localized nonbonding π-electron states exist in the exterior zigzag edges of graphene. These edge states confer upon these materials potential catalytic reactivity. Indeed, the as-prepared HGn can efficiently catalyze hydrogenation of nitrobenzene with isopropanol as the hydrogen donor. To our delight, we found selective transformation to aniline or azobenzene can be achieved with high yields in argon and hydrogen atmospheres, respectively. Carefully designed experiments demonstrated that a radical-based mechanism was predominant in these carbocatalytic reactions, which is different from the hydride transfer mechanism most often proposed in transition-metal-based catalysis. Zigzag edges have been considered to act as the radical initiator by donating a single electron to nitrobenzene molecules. The oxygen-containing groups can help the adsorption of both nitrobenzene and isopropanol onto the edges of the catalysts through H-bonds and dipolar-dipolar interactions. It is also predicted that these states chemically behave like a partial radical and are capable of activating a wide range of molecules for development of metal free catalysts.

Catalytic hydrogenation of nitrobenzene via intrinsic holey graphene nanoplatelets with rich zigzag edges

256th National Meeting (2018)

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