Mechanochemical Regulation of Oxidative Addition to a Palladium(0) Bisphosphine Complex

Here,
we report the effect of force applied to the biaryl backbone
of a bisphosphine ligand on the rate of oxidative addition of bromobenzene
to a ligand-coordinated palladium center. Local compressive and tensile
forces on the order of 100 pN were generated using a stiff stilbene
force probe. A compressive force increases the rate of oxidative addition,
whereas a tensile force decreases the rate, relative to that of the
parent complex of strain-free ligand. Rates vary by a factor of ∼6
across ∼340 pN of force applied to the complexes. The crystal
structures and DFT calculations support that force-induced perturbation
of the geometry of the reactant is negligible. The force-rate relationship
observed is mainly attributed to the coupling of force to nuclear
motion comprising the reaction coordinate. These observations inform
the development of catalysts whose activity can be tuned by an external
force that is adjusted within a catalytic cycle.