Résumé
Mechanocatalysis combines mechanical energy and chemical reactivity to perform solvent-free catalytic transformations. Direct mechanocatalysis involves using reactor-supported catalysts to boost reaction performances while avoiding solvents and energy-consuming post-reaction purification steps. This process aims at increasing the reaction yield and decreasing drastically the E-factor. Herein, we report the first examples of direct mechano-organocatalysis with a piperazine-based organocatalyst, covalently grafted onto amine-functionalized zirconia milling balls. This unprecedented milling system catalyzed Knoevenagel condensations under solvent-free conditions, operating faster (with a thousand-fold less catalyst used than that in traditional methods), achieving full conversion within only3 hours, and remained active after multiple reaction cycles. The turnover frequency (TOF) reached 5700 h -1 , far exceeding that of homogeneous analogues (40 h -1 ), due to the low catalyst loading and efficient energy transfer. Comprehensive surface characterization of the milling balls (XPS and original PM-IRRAS), before and after grafting, and after catalysis, elucidated the structure-activity relationship. This work establishes the first demonstration that a robust organocatalyst can be efficiently used in supported mechanocatalysis, highlighting the promise of surface-engineered zirconia systems for green chemistry.Green foundation 1. For the first time, covalently grafted organic catalytic species were shown to resist the demanding conditions of mechanochemistry without performance loss or catalyst release. This highly sustainable and resource-efficient durable organocatalytic system is completely solvent-free, with no solvent required for either the reaction or the purification. 2. This system addresses most of the pillars of green chemistry owing to zero use of solvent (both for the reaction and separation of chemicals) during the catalytic reaction: no waste production, atom economy, safer solvents, catalysis and energy efficiency. The specific green chemistry achievement is a high RME factor (around 90%) with an E-factor of nearly 0 (0.2), much lower than in equivalent solution chemistry or mechanochemical reactions (22 and 17, respectively). 3. The demonstrated concept of direct mechano-organocatalysis with catalysts supported on the milling system could be made greener by increasing the number of available catalytic sites to decrease the reaction time; tuning the nature of the catalyst will open large opportunities in future research.