Development of Ir(III) Photocatalysts Enabling Blue-Light-Induced Hydrocarboxylation of Unactivated Alkenes and Arenes

Novel types of CCC pincer Ir(III) organometallics with ligands of flexible seven-membered ring N-heterocyclic carbene (NHC) and 1,4-diimine are designed and developed as photocatalysts (PC1–PC3), which show the characteristic maximum absorption at the farther blue light region (λabs = 485–499 nm) than the usual commercial Ir(III) catalysts. Photocatalytic hydrocarboxylation using PC1 and PC2 with HCO2Cs under irradiation of blue LEDs has proven to be well-effective particularly toward unactivated internal alkenes and arenes, presenting a broad scope (>50 examples) and up to 95% yields and >20:1 regioselectivity as well. A mechanistic study proposes a photocatalytic process, which involves hydrogen atom transfer (HAT) and O–Ir(III) homolysis to generate the active Ir(III)–H species for catalytic cycling. This achievement offers a valuable example for possibly exploring the more potential photocatalytic reactivity of this system.