Enhanced Cyclopropanation of Norbornene as a High-Energy Fuel by Pd Single-Site Catalysts

Abstract

The high strain energy of the three-membered ring can increase the combustion calorific value of space fuels. At present, the cyclopropanation of alkenes is the bottleneck to obtain highly-energy three-member-ring fuels. In this article, Pd single-site catalysts (SSCs) were prepared to catalyze the cyclopropanation of norbornene. Pd²⁺ on the SSCs enhanced the adsorption of CH₂N₂ through electrostatic interaction, efficiently forming metal carbene. The conversion and selectivity of norbornene cyclopropanation reached 99.9% and 96.9%, which are much higher than those of commercial Pd/C (conversion 42.3%, selectivity 80.8%). In addition, the obtained tricyclooctane shows excellent properties (density 0.93 g/cm³, calorific value 42.75 MJ/kg) to be a promising high-performance rocket fuel. This work provides an efficient method for the synthesis of cyclopropane-based space fuels from alkenes.