Porous Co-SAC catalysed cyclopropanation via carbenoid C–C bond formation: an experimental and theoretical study

Abstract

Single-atom catalysts (SACs) have opened an emerging area in heterogeneous catalysis owing to their high substrate-specific designability and good recyclability. Till now, only three M-SACs (M = Rh, Ir, and Cu) have been explored for diazo activation, primarily towards N–H and O–H bond insertion reactions. However, Co-SAC-mediated diazo activation toward olefin cyclopropanation has not been reported yet. In this work, we present a Co-SAC system towards diazo activation, followed by electrophilic olefin cyclopropanation. Strategically designed silica template-mediated Co-SACs, having an electron-deficient cobalt center, offered exceptional catalytic activity compared to carbon-supported ones. The catalytic efficiency of the Co-SAC synthesized with a silica template (Cat 2) was found to be much higher than the carbon-supported one (Co1NC@C), as the Co(ii) center in Cat 2 was more electron-deficient than Co1NC@C, as reflected in XAS data with Cat 2 having a higher absorption energy and a shorter Co–N bond length. A wide range of aryl-substituted diazoesters and styrene derivatives were successfully converted into the corresponding intra- and intermolecular cyclopropanes in good to excellent yields. Various kinetic and control experiments were carried out to understand the plausible mechanism. DFT studies establish the thermodynamic feasibility of the reaction over the Co-SACs. Notably, the catalyst can be recycled up to 9 times without significant loss in catalytic activity. In this work, our intention was not to achieve the highest TON and TOF, but to investigate the feasibility of using a heterogeneous Co-SAC towards diazo activation and olefin cyclopropanation reactions. This journal is © The Royal Society of Chemistry, 2026.