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A diazulenylmethane dialdehyde reacted with dipyrrylmethanes in the presence of HCl or HBr, followed by oxidation with FeCl(3), to give aromatic adj-diazuliporphyrins. The free base structures must exist as mesoionic species, although these porphyrinoids were isolated as salts of the monoprotonated macrocycles. Reaction with Pd(OAc)(2) gave an unprecedented zwitterionic palladium(II) complex that was characterized by X-ray crystallography.
Zhang et al. (2008) studied this question.
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