Cyclic amino(alkyl) and cyclic amino(aryl) carbenes (cAACs/cAArCs) have been established as very useful ligands for catalytic and photonic applications of transition metal complexes. Herein, we describe the synthesis of a structurally related sterically demanding, electrophilic [2.2]isoindolinophanyl-based carbene (iPC) with a [2.2]paracyclophane moiety. The latter leads to more delocalized frontier orbitals and intense green fluorescence of (HiPC)OTf (2) from an intra-ligand charge transfer (1ILCT) state in the solid state. Base-promoted synthesis of the free carbene led to an unusual ring expansion and subsequent dimerization reaction, but the beneficial ligand properties can be exploited by trapping in situ at a metal center. The iPC ligand is a very potent π-chromophore, which participates in low energy metal-to-ligand (ML)CT transitions in [RhCl(CO)2(iPC)] (4) and IL-“through-space”-CT transitions in [Au(iPC)2]OTf (5). The steric demand of the iPC leads to high stability of 5 against air, moisture, or solvent attack, and ultralong-lived green phosphorescence with a lifetime of 185 μs is observed in solution. The beneficial photophysical and electronic properties of the iPC ligand, including a large accessible π surface area, were exploited by employing highly efficient energy transfer (EnT) photocatalysis in a [2+2] styrene cycloaddition reaction using 5, which outperformed other established photocatalysts in comparison.

中文翻译：

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[2.2]异吲哚啉基卡宾 (iPC) 配体：合成、电子和光物理性质以及在光催化中的应用**


环状氨基（烷基）和环状氨基（芳基）卡宾（cAAC/cAArC）已被确定为过渡金属络合物催化和光子应用中非常有用的配体。在此，我们描述了具有[2.2]对环芳烷部分的结构相关的空间要求的、亲电子的基于[2.2]异吲哚啉基的卡宾（iPC）的合成。后者导致来自固态配体内电荷转移 (1ILCT) 状态的 (HiPC)OTf (2) 更加离域前沿轨道和强烈的绿色荧光。碱促进的游离卡宾的合成导致了不寻常的环膨胀和随后的二聚反应，但可以通过在金属中心原位捕获来利用有益的配体特性。 iPC 配体是一种非常有效的 π 发色团，参与 [RhCl(CO)2(iPC)] (4) 和 IL-“through-space”-CT 中的低能金属到配体 (ML)CT 跃迁[Au(iPC)2]OTf (5) 中的跃迁。 iPC 的空间需求导致对空气、湿气或溶剂侵蚀具有 5 的高稳定性，并且在溶液中观察到寿命为 185 μs 的超长绿色磷光。通过在使用 5 的 [2+2] 苯乙烯环加成反应中采用高效能量转移 (EnT) 光催化，充分利用了 iPC 配体的有益光物理和电子特性，包括较大的可接近 π 表面积，其性能优于其他已建立的光催化剂。比较。