Izquierdo-García Patricia, Fernández-García Jesús M, Perles Josefina, Martín Nazario
Departamento de Química Orgánica I, Facultad de Ciencias Químicas, Universidad Complutense de Madrid, 28040 Madrid, Spain.
Laboratorio DRX Monocristal, SIdI, Universidad Autónoma de Madrid, 28049 Madrid, Spain.
J Am Chem Soc. 2024 Dec 18;146(50):34943-34949. doi: 10.1021/jacs.4c14544. Epub 2024 Dec 6.
The semiconductor properties of nanosized graphene fragments, known as molecular nanographenes, position them as exceptional candidates for next-generation optoelectronics. In addition to their remarkable optical and electronic features, chiral nanographenes exhibit high dissymmetry factors in circular dichroism and circularly polarized luminescence measurements. However, the synthesis of enantiomerically pure nanographenes remains a significant challenge. Typically, these materials are synthesized in their racemic form, followed by separation of the enantiomers using high-performance liquid chromatography (HPLC). While effective, this method often requires expensive instrumentation, extensive optimization of separation conditions, and typically yields analytical quantities of the desired samples. An alternative approach is the enantioselective synthesis of chiral molecular nanographenes; however, to date, only two examples have been documented in the literature. In this work, we present a straightforward chemical method for the chiral resolution of helical bilayer nanographenes. This approach enables the effective and scalable preparation of enantiomerically pure nanographenes while avoiding the need for HPLC. The incorporation of a BINOL core into the polyarene precursor facilitates the separation of diastereomers through esterification with enantiomerically pure camphorsulfonyl chloride. Following the separation of the diastereomers by standard chromatographic column, the hydrolysis of the camphorsulfonyl group yields enantiomerically pure nanographene precursors. The subsequent graphitization, achieved through the Scholl reaction, occurs in an enantiospecific manner and with the concomitant formation of a furan ring and a heterohelicene moiety. The absolute configurations of the final enantiomers, - and -, have been determined using X-ray diffraction. Additionally, electrochemical, photophysical, and chiroptical properties have been thoroughly evaluated.
被称为分子纳米石墨烯的纳米级石墨烯片段的半导体特性，使其成为下一代光电子学的优异候选材料。除了其卓越的光学和电子特性外，手性纳米石墨烯在圆二色性和圆偏振发光测量中表现出高不对称因子。然而，对映体纯的纳米石墨烯的合成仍然是一个重大挑战。通常，这些材料以消旋形式合成，然后使用高效液相色谱（HPLC）分离对映体。虽然有效，但这种方法通常需要昂贵的仪器、广泛优化分离条件，并且通常只能得到分析量的所需样品。另一种方法是手性分子纳米石墨烯的对映选择性合成；然而，迄今为止，文献中仅记录了两个实例。在这项工作中，我们提出了一种直接的化学方法用于螺旋双层纳米石墨烯的手性拆分。这种方法能够有效且可扩展地制备对映体纯的纳米石墨烯，同时避免了对HPLC的需求。将联萘酚核心引入多芳烃前体中，通过与对映体纯的樟脑磺酰氯酯化促进非对映异构体的分离。通过标准色谱柱分离非对映异构体后，樟脑磺酰基的水解产生对映体纯的纳米石墨烯前体。随后通过肖尔反应实现的石墨化以对映体特异性方式发生，并伴随呋喃环和杂螺旋烯部分的形成。最终对映体 - 和 - 的绝对构型已通过X射线衍射确定。此外，还对电化学、光物理和手性光学性质进行了全面评估。
