Efficient IrIII Photosensitizer Incorporated in the Metal-Organic Framework with the Bis-lophine-bipyridine Motif for C(sp3)-C/N-H Cross-Coupling Reactions

Photocatalytic technology offers a potential solution to energy and environmental issues. The performance of photocatalysts directly affects the efficiency of photocatalysis. Iridium(III)-based catalysts have garnered attention due to their unique electronic structure and high catalytic activity. However, most Ir-III catalysts are homogeneous and face issues such as low stability and difficulty in recycling. The research on heterogeneous Ir-III catalysts has become a hot topic, aiming to improve their stability and recyclability. In this study, we designed a tetracarboxylate ligand containing bipyridine modified with a bilophthalene unit, constructed a Zr-based metal-organic framework (MOF) with a 2-fold interpenetrating structure, and introduced [Ir-III(ppy)(2)](+) units through postmodification to form Ir@Zr-MOF. The heterostructure enhanced the utilization of light energy and photocatalytic efficiency. Apart from the electron transfer pathway between the original zirconium clusters and the bislophine-bipyridine unit, comparative studies of theoretical models showed that the introduction of the [Ir-III(ppy)(2)](+) unit reduced the energy level and enhanced the absorption of visible light in the 500-550 nm range, corresponding to the charge transfer between the modified bis-lophine-bipyridine and [Ir-III(ppy)(2)](+) unit. Ir@Zr-MOF, as a photocatalyst, can facilitate the trifluoromethylation of coumarins and the oxidative dehydrogenative coupling reaction of ethers with aryl hydrazones. The conversion yields of the related reactions can reach up to 95%. The mechanism presumes that the generation of superoxide radicals and the corresponding holes produced by Ir@Zr-MOF are crucial for the photocatalytic reaction. The generation of superoxide radicals can be verified by ESR. The host-guest interactions and hole effects of Ir@Zr-MOF with reaction substrates were also explored through theoretical simulations. This work provides a strategy for the heterogenization of Ir-III catalysts, offering insights for the preparation of photosensitizers and the enhancement of light energy utilization.