Collision Dynamics in Thermally-Controlled Ball Milling in Rh(I)-Catalyzed C−H/C−N Bond Activation: Mechanism and Hot−Spot Activity

Mechanochemical activation represents a powerful concept to harness mechanical force and drive chemical transformations in a solid state. Herein, we report a framework to determine the effect of temperature increase on mechanochemical ball milling in Rh(I)-catalyzed C−H/C−N activation. By using collision dynamics, we provide a model to determine the effect of ball size, milling frequency, internal jar length, velocity, material, and internal curvature during the collisions. By conducting computational studies, we investigate the reaction mechanism and the role of thermal mechanochemical collisions on C−H/C−N bond activation steps. Taking the solution-phase mechanism as a working hypothesis, the observed ball-milling acceleration is consistent with a proposal combining local temperature elevation at impact sites, estimated at up to 83.5 K above the bulk temperature, and modest, step-dependent mechanical modulation of selected transition states, while the rate-determining step is not significantly affected by compression. These results suggest that mechanical force can lower selected transition-state barriers at hot spots, offering a promising strategy for mechanochemical synthesis.