Light Induced Cobalt(III) Carbene Radical Formation from Dimethyl Malonate As Carbene Precursor

Radical-type carbene transfer catalysis is an efficient method for the direct functionalization of C–H and C═C bonds. However, carbene radical complexes are currently formed via high-energy carbene precursors, such as diazo compounds or iodonium ylides. Many of these carbene precursors require additional synthetic steps, have an explosive nature, or generate halogenated waste. Consequently, the utilization of carbene radical catalysis is limited by specific carbene precursors that access the carbene radical intermediate. In this study, we generate a cobalt(III) carbene radical complex from dimethyl malonate, which is commercially available and bench-stable. EPR and NMR spectroscopy were used to identify the intermediates and showed that the cobalt(III) carbene radical complex is formed upon light irradiation. In the presence of styrene, carbene transfer occurred, forming cyclopropane as the product. With this photochemical method, we demonstrate that dimethyl malonate can be used as an alternative carbene precursor in the formation of a cobalt(III) carbene radical complex.