Wydział Chemii

Ludmiła Szterenberg

Lechosław Latos-Grażyński

2001

Journal of Porphyrins and Phthalocyanines

5

474-480

10.1002/jpp.347

Naukowa

Angielski

Artykuł

The formation mechanism of the fused porphyrin (CTPPH-NF) involves a rotation of the N(2) pyrrole ring of 2-aza-21-carba-5,10,15,20-tetraarylporphyrin (CTPPH₂) which is subsequently followed by formation of the C(3)–N(24) bond to yield the macrocycle with the fused pyrrole tripentacyclic ring. To approach the problem of the relative stability of the prearranged transient species theoretical investigations have been performed applying density functional theory (DFT). The molecular structures and electronic energy have been studied for idealized 2-aza-21-carbaporphyrin (CPPH₂) and porphyrin (PH₂) macrocycles created by a replacement of phenyl or other substituents with hydrogen or methyl groups. The following forms of 2-aza-21-carbaporphyrin and porphyrin were studied: CPH₂-I, 2-NH-CPH-I and PH₂-I in relation to CPH₂-P, 2-NH-CPH-P and PH₂-P, respectively (P indicates regular geometry (N(21) or C(21) located in the inner perimeter) and I indicates inverted geometry (N(21) or C(21) located in the outer perimeter).A π delocalization exists through the inverted macrocycles: PH₂-I, CPH₂-I and 2-NH-CPH-I. The B3LYP/6-31G** optimized bond distances of I macrocycles reproduce the pattern of the P counterparts. The B3LYP/6-31G**//B3LYP/6-31G** calculated energy differences between the P and I structures are very similar for two considered 2-aza-21-carbaporphyrin tautomers: CPH₂-P → CPH₂-I, 18.50 kcal mol⁻¹, 2-NH-CPH-P → 2-NH-CPH-I, 17.55 kcal mol⁻¹; but essentially different for the regular porphyrin PH₂-P → PH₂-I, 45.56 kcal mol⁻¹. The methyl substitution at the 21-carbon or 5 and 20 meso positions preserved the order of stability as the calculated energy differences equal 21-CH₃-CPH₂-P → 21-CH₃-CPH₂-I, 13.39 kcal mol⁻¹; 5,20-CH₃-CPH₂-P → 5,20-CH₃-CPH₂-I, 17.87 kcal mol⁻¹.

https://doi.org/10.1002/jpp.347