Data from: Distal conformational locks on ferrocene mechanophores guide reaction pathways for increased mechanochemical reactivity

When incorporated into polymeric materials, mechanophores can be used to produce strain-dependent covalent chemical responses, including stress-strengthening, stress-sensing and network remodeling. In general, it is desirable for mechanophores to be highly inert in the absence of force but highly reactive under applied tension. Metallocenes possess remarkable combinations of force-free stability and force-coupled reactivity, but the mechanistic basis of this reactivity remains largely unexplored. Here, we use single molecule force spectroscopy to probe the mechanical reactivity of a series of ferrocenophanes and elucidate the mechanistic factors that dictate their mechanochemical activity. The force-coupled rate of cyclopentadiene (Cp) dissociation among various ferrocene derivatives varies by several orders of magnitude at ~1 nN, and the differences in reactivity are not correlated with ring strain in the reactants, but the extent of rotational realignment of the two Cp ligands. Mechanophores with pulling points that are conformationally restricted by distal attachments to an eclipsing orientation are most labile, whereas conformationally unrestricted ligands reorient under force to effectively superpose "catch bond" like contributions onto the overall mechanically assisted dissociation reaction. The ability to program the mechanism of ferrocene dissociation to proceed through ligand "peeling", as opposed to the more conventional "shearing" mechanism of the parent ferrocene, leads to enhanced macroscopic, multi-responsive behavior including mechanochromism and force-induced crosslinking in ferrocenophane-containing polymers.