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

Chemical reactions usually proceed through radical, concerted, or ionic mechanisms, yet transformations in which these three mechanisms take place at the same time 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 1H- and 19F-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 likely arises from a post- transition-state bifurcation in the reaction pathway, and their relative proportion is dictated by the polarisation of the scissile C–C bond.