Department of Chemistry and Biochemistry, University of Missouri, One University Boulevard, St. Louis, MO 63121, USA.
Molecules. 2023 Mar 17;28(6):2729. doi: 10.3390/molecules28062729.
Ferrocenium catalysis is a vibrant research area, and an increasing number of ferrocenium-catalyzed processes have been reported in the recent years. However, the ferrocenium cation is not very stable in solution, which may potentially hamper catalytic applications. In an effort to stabilize ferrocenium-type architectures by inserting a bridge between the cyclopentadienyl rings, we investigated two ferrocenophanium (or -ferrocenium) cations with respect to their stability and catalytic activity in propargylic substitution reactions. One of the ferrocenophanium complexes was characterized by single crystal X-ray diffraction. Cyclic voltammetry experiments of the ferrocenophane parent compounds were performed in the absence and presence of alcohol nucleophiles, and the stability of the cations in solution was judged based on the reversibility of the electron transfer. The experiments revealed a moderate stabilizing effect of the bridge, albeit the effect is not very pronounced or straightforward. Catalytic propargylic substitution test reactions revealed decreased activity of the ferrocenophanium cations compared to the ferrocenium cation. It appears that the somewhat stabilized ferrocenophanium cations show decreased catalytic activity.
二茂铁翁催化是一个活跃的研究领域，近年来已有越来越多的二茂铁催化过程被报道。然而，二茂铁阳离子在溶液中不太稳定，这可能会对催化应用造成潜在的阻碍。为了通过在茂环之间插入桥来稳定二茂铁型结构，我们研究了两个带有正电荷的茂铁（或二茂铁阳离子），以评估它们在丙炔基取代反应中的稳定性和催化活性。其中一个茂铁翁配合物通过单晶 X 射线衍射进行了表征。在不存在和存在醇亲核试剂的情况下，对茂铁翁母体化合物进行了循环伏安实验，并根据电子转移的可逆性来判断阳离子在溶液中的稳定性。实验表明，桥具有中等程度的稳定化作用，尽管这种作用不是非常显著或直接。与 ferrocenium 阳离子相比，催化丙炔基取代测试反应表明 ferrocenophanium 阳离子的活性降低。似乎稍微稳定的茂铁翁阳离子显示出降低的催化活性。
