Sustainable Synthesis of Diamondoid Ethers by High-Temperature Ball Milling

Abstract

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.

Diamondoid ether clusters in helium nanodroplets

“…1,1′-Diadamantyl ether ( 1 ) and 1-adamantyl-1-diamantyl ether ( 3 ) were synthesized according to previously published procedures, 29,33,35 while the preparation of 4,9-bis(1-adamantyloxy)diamantane ( 2 ) is first described here ( vide infra ).…”

“…3,4 Subsequently, the beam passes a skimmer and the helium droplets pick up the desired dopant species in a separately pumped chamber. Here, we dope the droplets with synthesized diamondoid ethers 1–3 (compounds 1 and 3 were previously described 29,33,35 and compound 2 was prepared using a similar procedure, vide supra ) using a heated gas-pickup cell (100 °C), which is connected to a heated reservoir (70 °C) via a precision leak valve. The doped He droplets then enter the differentially pumped analysis chamber, where a reflectron time-of-flight mass spectrometer KAESDORF RTF50 is utilized to record mass spectra.…”

“…As part of our investigation of covalent diamondoid assemblies consisting of two or more diamondoid cages connected with a heteroatom linker, we recently prepared a series of diamondoid ether derivatives. 29,33 We explored on-surface assemblies and capability of monolayer formation in a 2D environment and demonstrated the importance of LD interactions acting in such supramolecular systems. Some ether derivatives 34 were previously studied at HND conditions but as they were not as bulky as diamondoid ethers, they could not engage in numerous intermolecular C–H bond contacts that would produce a strong additive LD effect.…”

Direct in situ measurement of polymorphic transition temperatures under thermo-mechanochemical conditions

“…While performing DSC analysis of ADE prepared by thermo-mechanochemistry, 40 we observed an endotherm prior to its melting point (Fig. 2A).…”

Deriving kinetic insights from mechanochemically synthesized compounds using multivariate analysis (MCR-ALS) of powder X-ray diffraction data

“…1 The minimized use of solvents and energy required, together with performances generally fast and quantitative, make these reactions a valid alternative route for the preparation of various classes of compounds. 2–4 Apart from all the merits of this synthetic methodology, the limit of mechanochemistry is the poor mechanistic understanding of the solid-state transformations involved. Since the reactions may follow different paths with respect to conventional solution chemistry, the outcome of these reactions cannot be taken for granted, and scale-up of laboratory reactions is not an obvious procedure.…”