Acridine PNP-Pincer Ligands Enabling Transition Metal-Catalyzed Photoreactions

Transition metal-catalyzed reactions are developed together with ligands. While transition metal-catalyzed photoreactions have been extensively reported in recent years, the development of ligands for photoreactions is limited to only a few cases. Therefore, establishing ligands that shed light on transition metal-catalyzed photoreactions is an important research goal. We successfully synthesized four acridine-containing PNP-pincer ligands and formed transition metal complexes with Ni, Pd, Pt, Cu, and Co. We found that the platinum complex induced photoreactions of olefins under visible light irradiation: transfer hydrogenation, which required only a stoichiometric amount of hydrogen source, and hydroxy/alkoxy alkylation of olefins. These reactions did not proceed with existing well-known ligands, demonstrating that the development of photoreaction-oriented ligands reveals unknown reactivities of transition metals.

过渡金属催化反应的研发通常与配体的开发协同推进。尽管近年来过渡金属催化光反应已有大量报道，但针对光反应的配体开发仅局限于少数案例。因此，研发可揭示过渡金属催化光反应内在机制的配体，是一项重要的研究目标。本研究成功合成了4种含吖啶（acridine）的PNP钳型配体（PNP-pincer ligand），并与镍（Ni）、钯（Pd）、铂（Pt）、铜（Cu）及钴（Co）形成了过渡金属配合物。研究发现，该铂配合物可在可见光照射下诱导烯烃发生两类光反应：仅需化学计量氢源的转移氢化反应，以及烯烃的羟基/烷氧基烷基化反应。现有经典配体无法触发此类反应，这表明针对光反应开发的配体，能够揭示过渡金属此前未被发现的反应活性。