Mechanical Force Modulated Organometallic Transformations

Ph.D. Defense Stephen Craig, Ph.D, Advisor Ross Widenhoefer, Ph.D., Advisor Abstract: Mechanical forces are known to drive a range of covalent chemical reactions and have a number of applications, including access to new reaction pathways, polymer transformations, degradable polymers, stress/strain sensing in bulk materials, and the release of small molecules/protons. In switchable catalysis, mechanical forces have been mainly exploited to activate latent catalysts by unplugging inhibiting ligands. However, mechanical forces offer more opportunities beyond breaking bonds due in part to the reversibility and continuous/wide adjustability. As an complementary strategy, force may be applied to a spectator ligand to toggle the structure and reactivity of the transition metal complex incrementally and reversibly between multiple states, without incurring scissile events. Here we study force-activity relationships of elementary steps and isolated catalytic transformations under this strategy, to build knowledge toward such multi-state mechanocatalysts. We introduce force probe ligands, a series of macrocyclic bis(phosphine) ligands containing stiff-stilbene photoswitch, as tools to quantify force effect in microscopic steps. The results suggest opportunities to experimentally map geometry changes associated with reactions in transition metal complexes and potential strategies for force-modulated catalysis.