Synthesis of Triple-Stranded Complexes Using Bis(dipyrromethene) Ligands

The reaction of an α-free, β,β′-linked bis(dipyrromethene) ligand with Fe3+ or Co3+ led to noninterconvertible triple-stranded helicates and mesocates. In the present context, a stable α-free ligand 2 has been developed and complexation of ligands 1 and 2 with diamagnetic Co3+, Ga3+, and In3+ has been studied. The triple-stranded M213 (M = Ga, In) and M223 (M = Co, Ga, In) complexes were characterized using matrix-assisted laser desorption ionization time-of-flight spectrometry, 1H NMR and UV−vis spectroscopy, and X-ray crystallography. Again, the 1H NMR analysis showed that both the triple-stranded helicates and mesocates were generated in this metal-directed assembly. Consistent with our previous finding on coordinatively inert Co3+ complexes, variable-temperature NMR spectroscopy indicated that the triple-stranded helicate and mesocate of labile In3+ did not interconvert in solution, either. However, the diastereoselectivity of the M223 complexes was found to improve with an increase in the reaction temperature. Taken together, this study complements the coordination chemistry of poly(dipyrromethene) ligands and provides further insight into the formation of helicates versus mesocates.

无α位取代、β,β′-连接的双(二吡咯甲烯)配体（bis(dipyrromethene) ligand）与Fe³+或Co³+发生反应，可生成无法相互转化的三链螺旋配合物（triple-stranded helicates）与介旋配合物（mesocates）。本研究开发了一种稳定的无α位取代配体2，并对配体1和2分别与抗磁性Co³+、Ga³+及In³+的配位反应进行了探究。研究团队通过基质辅助激光解吸电离飞行时间质谱（matrix-assisted laser desorption ionization time-of-flight spectrometry）、核磁共振氢谱（¹H NMR）、紫外-可见光谱（UV−vis spectroscopy）以及X射线晶体学，对三链结构的M₂L₁₃（M=Ga、In）与M₂L₂₃（M=Co、Ga、In）配合物进行了表征。核磁共振氢谱分析结果进一步证实，在该金属导向组装过程中，三链螺旋配合物与介旋配合物均可形成。与此前关于配位惰性Co³+配合物的研究结论一致，变温核磁共振波谱分析显示，配位活性In³+形成的三链螺旋配合物与介旋配合物在溶液中同样无法相互转化。不过，M₂L₂₃配合物的非对映选择性随反应温度升高而显著提升。综上，本研究丰富了聚(二吡咯甲烯)配体的配位化学研究体系，并为螺旋配合物与介旋配合物的形成机理提供了更为深入的理论认知。