Rational Synthesis of 5,10-Diazaporphyrins via Nucleophilic Substitution Reactions of α,α′-Dibromotripyrrin and Dihydrogenation to Give 5,10-Diazachlorins

We report here the
first rational synthesis of 5,10-diazaporphyrins
via nucleophilic substitution reactions of α,α′-dibromotripyrrin.
Uses of 1,3-diiminoisoindoline and 3,4-di­(ethylsulfanyl)­pyrrole-2,5-diimine
as nucleophiles allowed for synthesis of 5,10-diazabenzoporphyrin
(2) and 5,10-diaza-7,8-di­(ethylsulfanyl)­porphyrin (3).
3 was reduced to 5,10-diazaporphyrin (4), 5,10-diaza-2,3-dihydrogenated
porphyrin (5), and 5,10-diaza-7,8-dihydrogenated porphyrin
(6) with yields that were dependent upon reduction conditions.
All the structures of these products were confirmed by X-ray crystallographic
analysis. Their optical and electrochemical properties have been comparatively
studied with those of 5,15-diazaporphyrin (7) and 5,15-diazachlorin
(8). Furthermore, NH tautomers of 2 and 4 were observed as different species in solution, and the
dynamic NH tautomeric behavior was studied in 4.