Three concomitant C–C dissociation pathways during the mechanical activation of an N-heterocyclic carbene precursor

Chemical reactions usually proceed through a radical, concerted or ionic mechanism; transformations in which all three mechanisms occur are rare. In polymer mechanochemistry, a mechanical force, transduced along polymer chains, is used to activate covalent bonds in mechanosensitive molecules (mechanophores). Cleavage of a C–C bond often follows a homolytic pathway, but some mechanophores have also been designed that react in a concerted or, more rarely, a heterolytic manner. Here, using 1 H- and 19 F-nuclear magnetic resonance spectroscopy in combination with deuterium labelling, we show that the dissociation of a mechanophore built around an N-heterocyclic carbene precursor proceeds with the rupture of a C–C bond through concomitant heterolytic, concerted and homolytic pathways. The distribution of products probably arises from a post-transition-state bifurcation in the reaction pathway, and their relative proportion is dictated by the polarization of the scissile C–C bond. Chemical reactions usually proceed through either a radical, concerted or ionic mechanism; transformations in which all three mechanisms occur are rare. Now, the mechanical dissociation of an N-heterocyclic carbene precursor has been shown to proceed with the rupture of a C–C bond through concomitant heterolytic, concerted and homolytic pathways.