カルボラン触媒を用いたハロゲン化反応の開発

抄録

Haloarenes have been appreciated as one of the most fundamental and versatile compounds in the modern chemistry field because the halide functionality offers numerous possible transformations into valuable building blocks. Although classical halogenation using molecular halogens (mainly Cl₂ and Br₂) and acid activators is still a promising protocol, it suffers from handling difficulties, low selectivity, and limited practical application in fine-chemical synthesis. To address this issue, the development of highly active yet efficiently selective halogenation methods has long been desired. In this article, we introduce carborane-based sulfide catalysts for aromatic halogenation. Carboranes (C₂B₁₀H₁₂) are three-dimensional aromatic molecules with icosahedral geometry, high thermal and chemical stabilities, and unique electronic effects. We envisioned that these boron clusters would be a handle to modulate the electronic property of halonium species, whereas their spherical shape exerts a negligible change in steric factor. As a specific design, we synthesized a series of sulfur-substituted carboranes and systematically studied their activity. Density functional theory (DFT) calculations revealed that the m-carborane scaffold was most suitable for catalysis, and the possible fine-tuning by decorating the cluster vertices was important for modulating the electronic property of halonium species to maximize the catalytic performance.

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