One-pot photocatalytic transformation of indolines into 3-thiocyanate indoles with new Ir(iii) photosensitizers bearing β-carbolines

• Published in: Inorganic chemistry frontiers 2021-03, Vol.8 (5), p.1253-1270
• Main Authors: Sanz-Villafruela, Juan, Martínez-Alonso, Carmen, Echevarría, Igor, Vaquero, Mónica, Carbayo, Arancha, Fidalgo, Jairo, Rodríguez, Ana M, José Vicente Cuevas-Vicario, Lima, João C, Moro, Artur J, Manzano, Blanca R, Jalón, Félix A, Espino, Gustavo
• Format: Article
• Language: English
• Subjects: Chemical reactions; Crystallography; Electrochemical analysis; Heterocyclic compounds; Indoles; Inorganic chemistry; Oxidizing agents; Photocatalysis; Room temperature; Sustainability; Thiocyanates
• ISSN: 2052-1545; 2052-1553
• DOI: 10.1039/d0qi01307b

Current societies demand sustainable synthetic procedures and accordingly the combination of two photocatalytic reactions in a one-pot process is a very appealing chemical tool. In the present work, we report on the development of new Ir(iii) bis-cyclometallated photosensitizers with β-carboline ligands and disclose a simple and unprecedented photocatalytic one-pot two-step protocol for the chemoselective and C-3 regioselective oxidative thiocyanation of indolines to produce the corresponding 3-thiocyanato-indoles. The procedure is performed in THF at room temperature, in the presence of NH4SCN, O2 and the Ir(iii) photocatalysts under blue light exposure. Moreover, this methodology combines important advantages such as an outstanding efficiency, based on good yields for low catalyst loadings, along with an excellent sustainability founded on the use of O2 as a green oxidant and light as the energy source. In addition, DFT studies have allowed a clear interpretation of the photophysical and electrochemical properties of the Ir(iii) complexes and transient absorption experiments, along with other experimental proof, have demonstrated that the two photocatalytic processes are mediated by 1O2. Our results pave the way for future developments in the field of photocatalysis using Ir(iii) biscyclometallated complexes as photosensitizers.