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Studies toward the chemistry of N-confused porphyrins Xiao, Ziwei

Abstract

The objectives of this work were to study the chemistry of N-confused porphyrins, which is a porphyrin isomer with an inverted pyrrole ring, and to develop new photosensitizers based on N-confused porphyrins for photodynamic therapy (PDT). Alkylation reactions of N-confused porphyrins were studied. N-confused tetraarylporphyrins reacted with CH₃ I in the presence of Na₂C0₃ to yield N,N'-dimethylated N - confused porphyrin salts 103 - 107, which are mixtures of structural isomers. The structures of the major isomers (III) were determined by X-ray diffraction and NMR spectroscopic analyses. These N,N'-dimethylated N-confused tetraarylporphyrin salts can generate singlet oxygen when irradiated with light of the appropriate wavelengths and are potential photosensitizers for PDT. The peripheral carbon-nitrogen double bonds of Ni(II) N-confused porphyrins are partially isolated from the 18 π conjugated aromatic system and reacted as dienophiles in Diels- Alder reactions with o-benzoquinodimethane yielding novel Ni(II) N-confused isoquinoporphyrins 133 (a-c). Ni(II) N-confused tetraphenylisoquinoporphyrin, 133a, was structurally characterized by X-ray diffraction analysis. Reaction of Ni(II) N-confused tetrakis(p-tolyl)porphyrin with NaOCH₃ and DDQ resulted in the inner C(21) cyanide addition product 146. Minor product 145 was presumably formed by subsequent nucleophilic addition of CH₃O⁻ to 146 at C(3) followed by oxidation with DDQ. Structures of both complexes 145 and 146 were determined by X-ray diffraction analyses. The Ni(III) complex of N-confused porphyrin inner C-oxide 153 was synthesized from oxidation of the precursor Ni(II) N-confused porphyrin using OSO₄. This Ni(III) complex has been structurally characterized.

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