365564-57-4Relevant academic research and scientific papers
Stabilization and Structure of the cis Tautomer of a Free-Base Porphyrin
Thomas, Kolle E.,McCormick, Laura J.,Vazquez-Lima, Hugo,Ghosh, Abhik
, p. 10088 - 10092 (2017)
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.
