Taming transient radical couplings by preassembling organophotocatalytic dyads

We report two organophotocatalytic dyads with distinct mechanisms that enable metal-free generation—and tame couplings—of transient carbon-centered radical partners. After forming their planar charge-transfer or charge-separated states, the dyads assemble non-covalently with radical precursors, and electron transfer reactivity is triggered by photoexcitation. Modulating the dyad's donor substituent diverts the mechanism from (1) consecutive photoinduced electron transfer via a radical anion catalyst/electron-acceptor substrate binary assembly to (2) a ternary assembly of a charge-separated catalyst and both partner substrates. In both cases, reductively generated alkenyl and alkynyl radicals couple with oxidatively activated trialkylamines in high efficiency, exquisite chemoselectivity, and excellent atom economy without the need for any transition metal co-catalyst—improving the sustainability of cross-couplings. Key to success was the intra-assembly generation and stabilization of transient radicals, preventing homocoupling/decomposition and furnishing a broad scope of products, including late-stage-functionalized drug molecules.