Ferrocenophanium Stability and Catalysis

Molecules. 2023 Mar 17;28(6):2729. doi: 10.3390/molecules28062729.

Abstract

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 ansa-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.

Keywords: catalyst stability; ferrocenophanium cations; propargylic substitution reactions.

Grants and funding

Support of this research by funds from the Banavali Green and Sustainable Chemistry Fund in Arts and Science at the University of Missouri – Saint Louis is gratefully acknowledged. The Office of the Vice Chancellor for Research and Economic & Community Development at UMSL is also gratefully acknowledged for support.