Mechanochemical generation of nitrogen-centred radicals for the formation of tertiary amines in polymers

Abstract

Force-activated functional groups in polymers may inform the design of future smart materials in which mechanical events trigger productive chemistry. The availability of such mechanochemically active tools (mechanophores) is perpetually increasing, but the limited understanding of mechanochemical reactivity complicates the identification of new molecular motifs that render reactive groups accessible by force. Here, we expand the chemical scope of our previously reported carbamoyloxime mechanophore motif from latent secondary to tertiary amines by harnessing the reactivity of transient nitrogen-centred radicals formed in the mechanochemical reaction pathway. Carbamoyloximes are modified with an N-pentenyl substituent which undergoes a consecutive intramolecular 5-exo-trig ring-closing reaction with an aminyl radical generated upon force-induced homolytic scission of the mechanophore, thereby enabling the hitherto unexplored mechanochemical activation of latent tertiary amines. We therefore show that carbamoyloxime mechanophores are nitrogen-centred mechanoradical generators expanding the chemical space of polymer mechanochemistry.