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.