Isotope Effect in the Activation of a Mechanophore

Abstract

In mechanochemistry, molecules under tension can react in unexpected ways. The reactivity of mechanophores (mechanosensitive molecules) can be controlled using various geometric or electronic factors. Often these factors affect the rate of mechanical activation but sometimes give rise to alternative reaction pathways. Here we show that a simple isotope substitution (H to D) leads to a reversal of selectivity in the activation of a mechanophore. Remarkably this isotope effect is not kinetic in nature but emerges from dynamic effects in which deuteration reduces the ability of the reactant to follow a post-transition-state concerted trajectory on the bifurcated force-modified potential energy surface. These results give a new insight into the reactivity of molecules under tension.

Heterocyclic Mechanophores in Polymer Mechanochemistry

“…The weak bonds are defined as chemical bonds with a bond-dissociation energy (BDE) of less than 72 kcal mol -1 ; they are generally found in acyclic structures. These include covalent bonds such as diazo, 23,47 C-S, [48][49][50] C-C (in tetraarylsuccinonitrile), 25,28,[51][52][53][54][55][56] C-O, 50,57,58 S-S, [59][60][61][62] (Figure 2a), and coordinative bonds such as Ru-carbene, Ag-carbene, or Cucarbene bonds, 16,63 Fe-Cp (in ferrocene), [64][65][66] Pt-acetylide, 67 Fe-pyridine, 68 Cu-naphthalene, 69 Pd-phosphine, 70 and Pdcarbene (Figure 2b). 71 Covalent bonds in strained ring structures have lower BDEs than the analogous linear structures and can respond to mechanical forces.…”

“…Indeed, as shown in Figure 1 , research on polymer mechanochemistry has exploded over the last ten years. This should be credited to Craig and other researchers (Boulatov, 24 Otsuka­, 25 Sijbesma, 16 Göstl, 8 Herrmann, 9 Robb, 26 Boydston, 27 De Bo, 28 Sottos 29 , Wang 4 and Xia, 30 among others).…”

A Perspective on the Force-Induced Heterolytic Bond Cleavage in Triarylmethane Mechanophores

“…Motifs that undergo the concerted cleavage of two or more weak bonds and afford neutral species are referred to as concerted. 28,29 Mechanophores creating radicals are subjected to homolytic cleavage, whereas the term heterolytic is conventionally invoked when charged species are generated. 1,30 All these descriptions are compatible with both scissile and non-scissile pathways.…”

Mechanochemical Organocatalysis: Do High Enantioselectivities Contradict What We Might Expect?

“…Mechanochemical processes use the input of mechanical force to affect a reaction. Typically, applied forces are either opposing in direction and result in the application of pulling forces to a mechanophore (using sonication devices or atomic force microscopes) or the forces converge on the reaction centre through impact [1–9] . Such converging forces can be achieved with a mortar and pestle, a simple hammer, a diamond anvil cell or perhaps most typically by a ball mill [10–31] .…”