THROUGH THE CHALLENGING SYNTHESIS OF TETRAPHENYLPORPHYRIN DERIVATIVES BEARING NITROXIDE MOIETIES
5
para-position of the meso-phenyl substituent for TPP-
CHO, TPP-NOH, TPP-NN, TPP-IN induces a small
bathochromic effect (4 nm) and a hyperchromic effect
(represented by the increase of the molar absorptivity e
of the band, Table 2).
TPP-NN and TPP-IN were also characterized by
MALDI-TOF mass spectroscopy. Both compounds
presented similar fragmentation of the radical moieties
(Figs 2 and 3). TPP-NN was detected as [M]+ whereas
TPP-IN was detected as [M + 2H]+ ion peaks at m/z =
769.751 and m/z = 755.814, respectively.
20-triphenylporphyrin (TPP-CHO), 5-[4-(4,4,5,5-tetra-
methyl-1,3-dihydroxy-2-imidazoline-2-yl)]-phenyl-
10,15,20-triphenyl-porphyrin (TPP-NOH), 5-[4-(4,4,5,5-
tetramethyl-2-imidazoline-3-oxide-1-oxyl-2-yl)]-phenyl-
10,15,20-triphenyl-porphyrin (TPP-NN), 5-[4-(4,4,5,5-
tetramethyl-1-oxyl-2-imidazoline-2-yl)]-phenyl-
10,15,20-triphenyl-porphyrin (TPP-IN).
Supporting information
Detailed experimental procedures and Figs (S1–
S7) not included in the text for brevity are given in the
supplementary material. This material is available free of
jpp/jpp.shtml.
CONCLUSION
In summary, for the first time free-base tetra-
phenylporphyrins bearing NN and IN on the para-
position of the meso-phenyl substituent were prepared.
This is an advancement towards achieving promising
novel radical architectures. TPP-CHO was obtained by
lithium–halogen exchange in 35% yield. Conversely,
the challenging incorporation of NN and IN moieties
was a success in spite of the high porphyrin aromaticity
and low solubility of TPP-CHO in methanol. The use
of a co-solvent, toluene, overcomes these disadvantages.
Moreover, the oxidation either by PbO2 or NaIO4 allows
access specifically to one targeted radical. The novel
compounds were non-ambiguously characterized by EPR
and UV-vis spectroscopy as well as MALDI-TOF mass
spectrometry. Further studies are underway to obtain
some metallated counterpart porphyrins and to study the
metal–radical interaction.
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Financial support from the Scientific and Technolo-
gical Research Council of Turkey-TÜBİTAK (project
113Z005) is gratefully acknowledged. The authors
declare no competing financial interest.
ABBREVIATIONS
Dimethylformamide (DMF), dichloromethane (DCM),
n-buthyllithium (n-BuLi), 5-(4-bromophenyl)-10,15,20-
triphenylporphyrin (TPP-Br), 5-(4-formylphenyl)-10,15,
Copyright © 2019 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2019; 23: 5–5