Synthesis and physicochemical characterization of a benzimidazole-phenol based Ir-complex and its evaluation on ketone-olefin coupling

HUNTER H. RIPBERGER; DANIEL A. HEREDIA; ANA L. MOORE; EMMANUEL ODELLA; THOMAS A. MOORE; S. JIMENA MORA; ROBERT R. KNOWLES

Colorado

Congreso; The 29th International Photochemistry Conference; 2019

The quantum efficiency of selected photoredox-based catalysis is frequently limited by the rapid charge recombination process between oxidizing equivalents (h+) and reducing equivalents (e-) formed upon initial illumination of the photocatalyst. An alternative to favor the forward processes over recombination reactions is the introduction of redox relays featuring proton-coupled electron transfer (PCET), which add fast redox-equivalent transfer steps that effectively compete against deleterious charge recombination at the charge-separating site.Herein we report the rational design, synthesis, electrochemical and spectroscopic characterization of a bioinspired Ir-based photocatalyst complex bearing a benzimidazole-phenol (BIP) moiety (Ir-BIP complex) and its evaluation on a model ketone-olefin cyclization.Preliminary results show remarkable fluorescence quenching of the Ir-BIP complex compared with the standard photocatalyst lacking the BIP moiety, suggesting a fast intramolecular PCET event, generating ground state Ir(II) and oxidized phenol. Initial evaluation of the Ir-BIP complex in a previously reported ketyl-olefin cyclization established that it is a competent photocatalyst in reductive PCET chemistry. Further spectroscopic characterization of the Ir-BIP complex, as well as a preliminary results in the application of the complex to improve quantum efficiency in the ketyl-olefin coupling, will be presented.In summary, we have developed a novel procedure for ketyl-olefin coupling allowed by PCET activation. These findings could be transferred to other photoinduced reactions, providing new strategies in the development of photocatalysts for reductive chemistry.