Angewandte Chemie: Squarephaneic Tetraanhydride

Our article reporting the synthesis and functionalisation of squarephaneic tetraanhydride, a unique new molecular building block, has been accepted for publication in Angewandte Chemie. As shown by the conversion into five different square­phaneic tetraimides and sodium squarephaneate, the new building block can be functionalised efficiently, yielding materials with highly interesting properties. Among other interesting features, it can be used for the synthesis of redox-active porous organic materials.

We have added some exciting new data since posting the preprint of the article on ChemRxiv. In the preprint, we claimed that the dianions of our squarephaneic tetraimides are globally aromatic and the tetraanions globally Baird aromatic. We have now added experimental evidence for this aromaticity switching upon reduction in the form of NMR spectra and EPR spectroelectrochemical measurements:

In the NMR spectra, we see that the phenylene-H signal splits into two signals upon reduction to the dianion, as the global aromaticity results in deshielding of the external Hs and in shielding of the internal Hs. The aliphatic signals are also slightly shifted.

EPR spectroelectrochemical measurements confirmed that the tetraanion is EPR active, providing evidence for its triplet nature and global Baird aromaticity.

S. Eder,# B. Ding,# D. B. Thornton, D. Sammut, A. J. P. White, F. Plasser, I. E. L. Stephens, M. Heeney, S. Mezzavilla, F. Glöcklhofer,* Squarephaneic Tetraanhydride: A Conjugated Square-Shaped Cyclophane for the Synthesis of Porous Organic Materials, Angew. Chem., Int. Ed. 2022, accepted article, DOI:10.1002/anie.202212623. [Link, open access]

(# contributed equally)