Tautomerism-Induced Cis–Trans Isomerization of Pyridylethenyl N‑Confused Porphyrin

Pyridylethenyl-substituted N-confused porphyrins (NCPs) were synthesized, and their cis–trans isomerization was studied. Among four possible isomers, trans-3H and cis-2H types of structures, of which aromaticity and absorption/emission properties differ largely, were isolated. The cis-isomer was lar...

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Veröffentlicht in:Journal of organic chemistry 2017-08, Vol.82 (16), p.8686-8696
Hauptverfasser: Sakashita, Ryuichi, Oka, Yasutaka, Akimaru, Hisanori, Kesavan, Praseetha E, Ishida, Masatoshi, Toganoh, Motoki, Ishizuka, Tomoya, Mori, Shigeki, Furuta, Hiroyuki
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Sprache:eng
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Zusammenfassung:Pyridylethenyl-substituted N-confused porphyrins (NCPs) were synthesized, and their cis–trans isomerization was studied. Among four possible isomers, trans-3H and cis-2H types of structures, of which aromaticity and absorption/emission properties differ largely, were isolated. The cis-isomer was largely stabilized by the intramolecular hydrogen bonding between the pyrrolic-NH and the pyridinic-N in the vicinity. The thermal cis–trans isomerization proceeded even at 30 °C, which was significantly accelerated by the pyridine added to the system. The kinetic studies revealed that the isomerization reaction was second-order and the activation energy of the thermal isomerization from cis to trans isomer was ΔG 0 ⧧ cis→trans = 35.7 kcal/mol at 298 K, which is significantly smaller than that of Ni complex (42.3 kcal/mol). An intermolecular proton transfer induced cis–trans isomerization mechanism was proposed.
ISSN:0022-3263
1520-6904
DOI:10.1021/acs.joc.7b01770