Blue-Emissive Cobalt(III) Complexes and Their Use in the Photocatalytic Trifluoromethylation of Polycyclic Aromatic Hydrocarbons.

Room-temperature luminescent CoIII complexes (1 and 2) are presented that exhibit intense ligand-to-metal and ligand-to-ligand charge transfer absorption in the low-energy UV region (λabs ≈360-400 nm) and low-negative quasi-reversible reduction events (E1/2(red) =-0.58 V and -0.39 V vs. SCE for 1 and 2, respectively). The blue emission of 1 and 2 at RT is due to the large bite angles and strong σ-donation of the ligands, the combined effect of which helps to separate the emissive 3 LMCT (triplet ligand-to-metal charge transfer) and the non-emissive 3 MC (triplet metal-centered) states. 1 and 2 were found to be powerful photo-oxidants (ECoIII*/CoII =2.26 V and 2.75 V vs. SCE of 1 and 2, respectively) and were used as inexpensive photoredox catalysts for the regioselective mono(trifluoromethylation) of polycyclic aromatic hydrocarbons (PAHs) in good yields (ca. 40-58 %).