Facile dearomatisation of porphyrins using palladium-catalysed hydrazination: the 5, 15-diiminoporphodimethenes and their redox products

Louisa Esdaile, Grace Simpkins, Oliver Locos, Llew Rintoul, Martin Duriska, Peter Turner, John McMurtrie, Dennis Arnold

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    Abstract

    The synthesis, electronic absorption and 1H NMR spectra of a suite of novel porphyrinoids derived from meso-bromoporphyrins by palladium-catalysed aminations using ethyl and tert-butylcarbazates are reported. Instead of the expected carbazate-substituted porphyrins, a facile oxidative dearomatisation of the porphyrin ring occurs in high yield, especially for the nickel(II) complexes, resulting in high yields of 5,15- diiminoporphodimethenes (DIPDs). The analogous zinc(II) and free base DIPDs were also characterised, the former by X-ray crystallography. The oxidation and reduction reactions of DIPDs and their precursor carbazate porphyrins were studied. Density Functional Theory (DFT) was used to calculate the optimised geometries and frontier molecular orbitals of DIPD Ni8c and bis(azocarboxylate) 19c, and Time Dependent DFT calculations allowed the prediction of electronic absorption spectra, whose characteristics corresponded well with those of the observed solution spectra. In the latter case, the calculated low-energy absorptions were unlike those of a typical porphyrin, due to the near-degeneracy of the highest filled frontier orbitals, and the wide energy separation between the unfilled orbitals. This feature was present in the observed spectrum.

    Original languageEnglish
    Pages (from-to)517-532
    Number of pages16
    JournalTetrahedron
    Volume70
    Issue number2
    DOIs
    Publication statusPublished - 2014

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    Esdaile, L., Simpkins, G., Locos, O., Rintoul, L., Duriska, M., Turner, P., McMurtrie, J., & Arnold, D. (2014). Facile dearomatisation of porphyrins using palladium-catalysed hydrazination: the 5, 15-diiminoporphodimethenes and their redox products. Tetrahedron, 70(2), 517-532. https://doi.org/10.1016/j.tet.2013.11.006