Substituted epoxy alcohols and amines allow substrate-controlled conversion of CO2 into a wide range of heterocyclic structures through different mechanistic manifolds. This new approach results in an unusual scope of CO2-derived products by initial activation of CO2 through either the amine or alcohol unit, thus providing nucleophiles for intramolecular epoxy ring opening under mild reaction conditions. Control experiments support the crucial role of the amine/alcohol fragment in this process with the nucleophile-assisted ring-opening step following an SN i pathway, and a 5-exo-tet cyclization, thus leading to heterocyclic scaffolds.

The interplay of opposing stabilities between terminal and N-bridging carbene (radical) moieties dictated by the Co II/IIIredox cycle plays an important role, and explains the unique active participation of the otherwise catalytically inactive N-enolate species. We envision that further application of these unique Co III -carbene radicals has the potential to unlock new scaffolds via the superior facile activation of acceptor-acceptor iodonium ylides over diazo compounds. Supporting InformationExperimental details; synthetic procedures; catalytic studies; XRD, EPR, NMR, UV/Vis, in-situ ATR-FT-IR and CSI + -MS spectroscopic data, (additional) DFT and NEVPT2-CASSCF calculations.

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Discovered as organometallic curiosities in the 1970s, carbene radicals have become a staple in modern-day homogeneous catalysis. Carbene radicals exhibit nucleophilic radical-type reactivity orthogonal to classical electrophilic diamagnetic Fischer carbenes. Their successful catalytic application has led to the synthesis of a myriad of carbo- and heterocycles, ranging from simple cyclopropanes to more challenging eight-membered rings. The field has matured to employ densely functionalized chiral porphyrin-based platforms that exhibit high enantio-, regio-, and stereoselectivity. Thus far the focus has largely been on cobalt-based systems, but interest has been growing for the past few years to expand the application of carbene radicals to other transition metals. This Perspective covers the advances made since 2011 and gives an overview on the coordination chemistry, reactivity, and catalytic application of carbene radical species using transition metal complexes and catalysts.