Carbaporphyrins, porphyrin analogues in which one or more of the internal nitrogen atoms have been replaced by methine units, have been widely investigated due to their intriguing chemical reactivity. Recently, the first example of an adj-dicarbaporphyrin 1a was reported and this reacted with Pd(OAc)2 to give a unique palladium(IV) sandwich complex. In this work, a series of adj-dicarbaporphyrins have been synthesized and the reactivity of this system has been further probed. 5-Unsubstituted pyrrole esters were prepared using the Barton-Zard reaction and converted into a series of dipyrrylmethane dialdehydes 2b-d. Base-catalyzed MacDonald condensation with bis(indenyl)methane 3 gave of dicarbaporphyrins 1b-d in 20-35% yield. These porphyrinoids exhibit strongly aromatic characteristics and the proton NMR spectra showed resonances for the internal CH and NH protons between -4 and -6 ppm. Reaction of 1a-d with di--chloro-tetracarbonyldirhodium(I) afforded the stable rhodium(III) complexes 4. The 1H NMR spectra of 4 clearly showed rhodium-hydrogen coupling and the retention of a strongly aromatic ring current.

Synthesis and metalation of adj-dicarbaporphyrins

253rd National Meeting (2017)

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