Single-Site Pd Regulated by π-π Stacking for High-Selectivity Cyclopropanation Reaction.

Cyclopropane-based high-energy fuels possess high intramolecular energy and density, and their precise synthesis is a critical challenge. However, owing to the highest strain in the cyclopropane structure (compared to other four- or five-membered rings, etc.), metal-carbene intermediates form with difficulty, resulting in poor catalytic selectivity for its synthesis. Herein, through rational design of π-π stacking between the Pd organic complex and graphene, we report a single-site Pd catalyst for precise synthesis of multicyclopropane-based high-energy fuels. It is discovered that π-π stacking enhanced the electrophilicity of Pd through a weak metal-support interaction, thus promoting the formation of Pd═C carbene active intermediates. Meanwhile, the adsorption between the active centers and intermediates was enhanced via π-π stacking. These two respects led to almost twice selectivity for cyclopropanation reaction up to 80.5% as that without π-π stacking. This work provides an effective strategy of π-π noncovalent interactions for regulating C-C coupling reaction selectivity.