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

Abstract

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 bis-lophine-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.