Periodic Reporting for period 1 - CAPELE (Chemical Catalysis with Piezoelectric Materials)
Période du rapport: 2023-07-01 au 2025-12-31
Activation of small organic molecules is the main objective of organic synthesis. To make molecules react, we usually have to give them energy, but the simplest method (i.e. heating up the reaction mixture) often fails due to issues with selectivity – the compounds decompose at higher temperatures. Ergo, alternate methods of activation are needed. Single electron transfer – giving or taking electrons from molecules can be used in this manner: weak bonds can be broken after an electron is accepted by the molecule, and new electrophilic centers are formed when an electron is abstracted from a molecule. The last 20 years brought a revival of organic photochemistry and electrochemistry as the researchers realized the potential of these techniques in activating molecules by single electron transfer.
Mechanochemistry is a well-developed field, as the mechanical milling is an extremely common process in industry – most complex operations require milling of the solids at some point, therefore the technology necessary for milling is well developed and understood. The potential of mechanochemistry to drive reactions requiring single electron transfer was discovered only recently – with the advent of catalysis with piezoelectric materials (materials that undergo charge separation when mechanical stress is applied to them). The main objective of this ERC grant is do develop new processes where reactions would be induced by single electron transfer under mechanochemical conditions.
Mechanochemistry is a well-developed field, as the mechanical milling is an extremely common process in industry – most complex operations require milling of the solids at some point, therefore the technology necessary for milling is well developed and understood. The potential of mechanochemistry to drive reactions requiring single electron transfer was discovered only recently – with the advent of catalysis with piezoelectric materials (materials that undergo charge separation when mechanical stress is applied to them). The main objective of this ERC grant is do develop new processes where reactions would be induced by single electron transfer under mechanochemical conditions.
We have investigated the feasibility of performing different types of reactions using mechanochemistry to induce single electron transfer in small organic molecules. The main types investigated are isomerizations, cyclizations, aromatic substitutions and reactions that are net redox neutral despite involving a single electron transfer in their mechanism. Most of this work is still ongoing. An already finished project is the radical nitration of electron-rich aromatic compounds using iron(III) nitrate as the nitrating reagent under mechanochemical conditions (Synlett 2025, 1397). Importantly, this reaction proceeds as a mono-nitration even when very electron-rich substrates are used, which is often hard to achieve using conventional nitration protocols. The reaction could be scaled up, making it attractive from an application standpoint.
So far, our main unexpected discovery occurred as this project was starting (Eur. J. Org. Chem. 2023, e202201399). We have discovered, that EDA complexes – complexes where one component acts as a donor of electrons and the other acts as the acceptor – can be also formed in solid phase, and that the electron transfer within these complexes can occur under mechanical stress. In such case no piezoelectric material is required for the single electron transfer to occur. We are currently researching the possible applications of this mechanism of activation. The radical nitration under mechanochemical conditions that we developed (Synlett 2025, 1397), was developed using this strategy.