Acceleration of Diels-Alder reactions by mechanical distortion
Yerzhan S. Zholdassov, L. Yuan, Sergio Romero Garcia, R. W. M. Kwok, Alejandro Boscoboinik, Daniel J. Valles, Mateusz Marianski, Ashlie Martini, Robert W. Carpick, Adam B. Braunschweig
Abstract
Challenges in quantifying how force affects bond formation have hindered the widespread adoption of mechanochemistry. We used parallel tip-based methods to determine reaction rates, activation energies, and activation volumes of force-accelerated [4+2] Diels-Alder cycloadditions between surface-immobilized anthracene and four dienophiles that differ in electronic and steric demand. The rate dependences on pressure were unexpectedly strong, and substantial differences were observed between the dienophiles. Multiscale modeling demonstrated that in proximity to a surface, mechanochemical trajectories ensued that were distinct from those observed solvothermally or under hydrostatic pressure. These results provide a framework for anticipating how experimental geometry, molecular confinement, and directed force contribute to mechanochemical kinetics.