Photocatalytic C–H Thiocyanation of Corroles: Development of Near-Infrared (NIR)-Emissive Dyes

Abstract

A new method of activating corrole macrocycles via an in situ generated SCN radical has been developed at very mild conditions at room temperature. This photoredox reaction resulted in the generation of tetrathiocyanatocorroles in good yields. The synthesis of tetrathiocyanatocorroles was never reported earlier. Single-crystal XRD analysis reveals that the insertion of four thiocyanate moieties at the four β-pyrrolic positions has imparted significant distortion to the corrole macrocycle. The generated tetrathiocyanatocorroles are different from the parent corroles in many ways. The photophysical properties of the newly synthesized tetrathiocyanatocorroles are dramatically altered from the parent corroles. The absorption feature of these modified corrole derivatives (both position and intensity) bears a nice similarity with the chlorophyll-a macrocycle. Thus, these newly synthesized molecules can be considered as spectroscopic model systems for chlorophyll-a pigments. The observed absorption and emission spectra of these tetrathiocyanatocorroles certainly point out that these newly developed ligand scaffolds and their various metal complexes will have immense potential as pigments in solar cells and also as NIR-emissive dyes. The observed C-H•••Au weak interactions in a representative Au(III)-corrole complex point out that these complexes are capable of activating the unfunctionalized C−H groups and thus will have potential implications in C-H activation reactions.

Oxo(corrolato)vanadium(iv) catalyzed epoxidation: oxo(peroxo)(corrolato)vanadium(v) is the true catalytic species

“…Corrole, a contracted porphyrin analog, is known to stabilize metals in a higher oxidation state. [30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49] Corrole has excellent chelating properties; many metal complexes across the periodic table bearing corrole ligand functionalities have already been reported in the literature. [50][51][52][53][54][55][56][57][58][59][60][61][62][63] Licoccia et al first synthesized oxo(corrolato)vanadium(IV) complexes bearing b-substitution at the corrole periphery.…”

Corroles at work: a small macrocycle for great applications

“…99). 278 The irradiation was carried out at room temperature in acetonitrile using a standard 20 W CFL (Compact Fluorescent Lamps) lamp. The tetra-thiocyanatocorrole was the main isolated compound after 5 hours of reaction.…”

“…A mechanism was proposed, involving radical species, and the formation of radical anion species was further confirmed by EPR. 278…”

Recent advances in photochemical and electrochemically induced thiocyanation: a greener approach for SCN-containing compound formation

“…Kar et al succeeded in developing a novel synthetic process for the simple synthesis of a novel class of corrole ligands 77 with four thiocyanate groups at the four surrounding β-positions in the corrole framework. 32 They used an SCN radical created in situ to activate corrole macrocycles 76 at ambient temperature and fabricate tetrathio-cyanatocorroles 77 in high to excellent yields. The absorption properties of the modified corrole derivatives are strikingly similar to those of chlorophyll-a macrocycle.…”