Single-Site\nPd Regulated by π−π\nStacking for High-Selectivity Cyclopropanation Reaction

Cyclopropane-based high-energy fuels\npossess high intramolecular\nenergy and density, and their precise synthesis is a critical challenge.\nHowever, owing to the highest strain in the cyclopropane structure\n(compared to other four- or five-membered rings, etc.), metal-carbene\nintermediates form with difficulty, resulting in poor catalytic selectivity\nfor its synthesis. Herein, through rational design of π−π\nstacking between the Pd organic complex and graphene, we report a\nsingle-site Pd catalyst for precise synthesis of multicyclopropane-based\nhigh-energy fuels. It is discovered that π−π stacking\nenhanced the electrophilicity of Pd through a weak metal−support\ninteraction, thus promoting the formation of PdC carbene active\nintermediates. Meanwhile, the adsorption between the active centers\nand intermediates was enhanced via π−π stacking.\nThese two respects led to almost twice selectivity for cyclopropanation\nreaction up to 80.5% as that without π−π stacking.\nThis work provides an effective strategy of π−π\nnoncovalent interactions for regulating C−C coupling reaction\nselectivity.