Sustainable Synthesis of Diamondoid Ethers by High-Temperature Ball Milling

Diamondoids have emerged as promising carbon-based nanomaterial building blocks because of their unique combination of exceptional properties and availability for selective functionalization. Until now, the chemical functionalization of diamondoids was primarily based on solution methods. However, the limited solubility of diamondoid derivatives and their tendency to sublimate at even slightly elevated temperatures made it difficult to prepare more extensive diamondoid scaffolds. Here, we present the first mechanochemical synthesis of several diamondoid ethers differing in the type, size, and number of their hydrocarbon cage subunits. We found that the efficient preparation of these ethers is enabled solely by high-temperature ball milling conditions and does not proceed under ambient conditions. When compared to the conventional synthesis of the same ether derivatives, the calculated green chemistry metrics showed the enormous sustainability benefits of the mechanochemical synthesis. The mechanochemical approach includes shorter reaction times, a green inorganic base, a simplified workup procedure, comparable or superior reaction yields, and the elimination of solvents in the synthesis. Furthermore, crystal structures obtained from single-crystal X-ray diffraction experiments confirmed the molecular structures of the target products and gave insight into their intermolecular interactions in the solid state. From the perspective of the future applicability of these materials in nanotechnology, the cost and sustainability of their preparation are paramount. We demonstrated herein that mechanochemistry is a viable option for this challenge.