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

Abstract

Room-temperature luminescent Co III complexes (1 and 2)a re presented that exhibit intense ligand-to-metal and ligand-to-ligand charge transfer absorption in the low-energy UV region (l abs % 360-400 nm) and low-negative quasi-reversible reduction events (E 1/2 (red) = À0.58 Vand À0.39 Vvs. SCE for 1 and 2,respectively). The blue emission of 1 and 2 at RT is due to the large bite angles and strong s-donation of the ligands,t he combined effect of whichh elps 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 (E Co III * =Co II = 2.26 V and 2.75 Vvs. 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 %).

Ultrafast and long-time excited state kinetics of an NIR-emissive vanadium(iii) complex I: synthesis, spectroscopy and static quantum chemistry

“…[13][14][15][16][17][18] The 3d transition metals possess a weaker ligand eld splitting 10 and smaller SOCs 11 posing severe challenges to the design of the excited state landscape, 14 yet several recent breakthroughs have been reported, e.g. on copper(I), 23,24 nickel(0,II), 25,26 cobalt(III), 27 iron(II,III), [28][29][30][31] chromium(0/III) [32][33][34][35] and vanadium(III). 36 Beyond the conventionally exploited MLCT excited states, 12 LMCT states of the low-spin d 5 electron conguration of iron(III) 18 and spin-ip states of the d 3 electron conguration of chromium(III) 15 are emerging as novel paradigmatic excited states useful for photoapplications.…”

Microsecond Photoluminescence and Photoreactivity of a Metal-Centered Excited State in a Hexacarbene–Co(III) Complex

“…Earth-abundant transition metal complexes have received increasing attention in recent years as photoactive components in prospective large-scale approaches for solar energy conversion and photocatalysis. − Several first-row transition metals are interesting in this context, but unfortunately many 3d metal complexes suffer from short excited-state lifetimes compared to their 4d and 5d congeners. , This is due to the presence of low-lying metal-centered (MC) states that facilitate fast, radiationless deactivation which limits their use in light-driven applications. − Nevertheless, significant progress has recently been made to extend the excited-state lifetimes of 3d metal complexes, for example, by innovative ligand design to destabilize MC states by imposing a strong ligand field , or by expanding investigations to a range of unconventional excited-state schemes beyond the common triplet metal-to-ligand charge transfer ( 3 MLCT) state in d 6 complexes. , Though MC states are interesting for spin crossover (SCO) and light-induced excited-state spin trapping (LIESST) applications, , in contrast to charge transfer (CT) states they are typically too low in energy to be interesting for photochemical applications or to display visible emission. , As a rare case among the d 6 complexes, very weak emission was reported from the 3 MC state in [Co­(CN) 6 ] 3– , , while such states have only rarely been possible to observe in Ru­(II) and Fe­(II) complexes. , Recently, remarkable photoproperties for Co­(III) complexes were reported by Hannan and Zysman-Coleman and co-workers . Excited states of mixed triplet ligand-to-metal charge transfer/ligand centered ( 3 LMCT/LC) character showed up to 8.7 ns blue emission in solution at room temperature.…”

“…19,20 Recently, remarkable photoproperties for Co(III) complexes were reported by Hannan and Zysman-Coleman and co-workers. 21 Excited states of mixed triplet ligand-to-metal charge transfer/ligand centered ( 3 LMCT/LC) character showed up to 8.7 ns blue emission in solution at room temperature. The photophysical properties of these complexes were related to the strong σ-donor ligands they contain.…”

An Earth-abundant cobalt based photocatalyst: visible light induced direct (het)arene C–H arylation and CO2 capture

“…16 Similarly, Eli Zysman-Colman et al designed a blue-emissive cobalt(III) complex which was further utilized for the photocatalytic trifluoromethylation of polycyclic aromatic hydrocarbons. 17 Despite remarkable advances, 7,8,18 only a few or limited examples involving cobalt complexes as photocatalysts toward organic transformations under ambient reaction conditions have been reported so far, [19][20][21] among which Co(PPz) 3 and Co(BPy) 3 have been successfully employed in the field of solar cells. 22,23 Although homogeneous photocatalysts exhibit superior catalytic performance, the cost associated with them, difficulty in recovering the catalyst from the reaction mixture, their toxicity profiles and complicated synthetic procedures present major barriers to applicability on a commercial scale.…”

“…2b). 17,42,43 The powder X-ray diffraction (PXRD) technique has been utilized to determine the crystal phase structure of the fabricated photo nanocatalyst. It can be seen in Fig.…”