Details

Autor(en) / Beteiligte

• Thomas, Kolle E.
• McCormick, Laura J.
• Vazquez‐Lima, Hugo
• Ghosh, Abhik

Titel

Stabilization and Structure of the cis Tautomer of a Free‐Base Porphyrin

Ist Teil von

• Angewandte Chemie (International ed.), 2017-08, Vol.56 (34), p.10088-10092

Ort / Verlag

Germany: Wiley

Erscheinungsjahr

2017

Link zum Volltext

Quelle

Alma/SFX Local Collection

Beschreibungen/Notizen

• Single‐crystal X‐ray analysis of the β‐heptakis(trifluoromethyl)‐meso‐tetrakis(p‐fluorophenyl)porphyrin, H2[(CF3)7TpFPP], has revealed the first example of a stable cis tautomer of a free‐base porphyrin, the long‐postulated intermediate of porphyrin tautomerism. The stability of the unique molecule appears to reflect a dual origin: a strongly saddled porphyrin skeleton, which alleviates electrostatic repulsion between the two NH protons, and two polarization‐enhanced, transannular N−H⋅⋅⋅O−H⋅⋅⋅N hydrogen bond chains, each involving a molecule of water. DFT calculations suggest that the observed tautomer has a lower energy than the alternative, doubly hydrated trans tautomer by some 8.3 kcal mol−1. A fascinating prospect thus exists that H2[(CF3)7TpFPP]⋅2 H2O and cognate structures may act as supramolecular synthons, which, given their chirality, may even be amenable to resolution into optically pure enantiomers. White whale of porphyrin researchers: The elusive cis tautomer of a free‐base porphyrin has been isolated and structurally characterized for the first time. X‐ray diffraction data show the presence of an unusual cis geometry. DFT calculations confirm the greater stability of this structure relative to the more commonly observed trans geometry.