Photoinduced Ligand-to-Metal Charge Transfer of Cobaltocene: Radical Release and Catalytic Cyclotrimerization

Irradiation of cobalt metallocenes at the ligand-to-metal charge transfer energies results in the labilization of the cyclopentadienyl-cobalt bond and radical release. The cyclopentadienyl radical is detected by electron paramagnetic resonance (EPR) spectroscopy using a spin trap and can also be chemically trapped using hydrogen-atom-donating reagents. This reaction presents a new photochemical method of generating new cobalt complexes or of forming cyclopentadienyl cobalt(I) species that are active for catalytic [2 + 2 + 2] cyclotrimerization reactions. More importantly, these results also show that cobaltocene should not be considered as a photostable redox reagent under many conditions, including those relevant to photovoltaics or photocatalysis.

Automated summary

Irradiating cobalt metallocenes at specific energies causes the destabilization of the cyclopentadienyl-cobalt bond and the release of radicals. These radicals can be detected by EPR spectroscopy and chemically captured using hydrogen-atom-donating reagents. This reaction offers a new photochemical method for generating cobalt complexes or catalytic cyclopentadienyl cobalt(I) species for [2 + 2 + 2] cyclotrimerization reactions. Additionally, the results highlight that cobaltocene is not a photostable redox reagent under various conditions, including those relevant to photovoltaics or photocatalysis.