Leveraging Metallotropism-Enabled Substrate Activation in Cobalt-Catalyzed Annulation Chemistry: Protic NHC Template Is the Key

This study introduces the access of protic NHC (pNHC) complexes with Cp*Co­(III) species via metallotropism-triggered activation of ubiquitous azole substrates. These “Co^III-pNHC” templates were further explored in catalytic annulative functionalization of azoles with internal alkynes, providing a variety of π-extended polycyclic heteroarene compounds. Mechanistic investigations via isolation and structure elucidation of the key pNHC-Co intermediates followed by control stoichiometric and catalytic reactions highlighted the crucial electronic control on the azole C–H activation, alkyne insertion, and regiodivergent annulation steps involved in this catalytic protocol. These results demonstrate that the cobalt-based metallotropism can act as a potentially useful platform toward earth-abundant first-row transition metal-catalyzed C–H functionalization, complementary to the dominant noble metal-based strategies.