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Title: Stabilization and Structure of the cis Tautomer of a Free-Base Porphyrin

Single-crystal X-ray analysis of the β-heptakis(trifluoromethyl)-meso-tetrakis(p-fluorophenyl)porphyrin, H 2[(CF 3) 7T pFPP], 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 H 2[(CF 3) 7T pFPP]∙ 2H 2O and cognate structures may act as supramolecular synthons, which, given their chirality, may even be amenable to resolution into optically pure enantiomers.
Authors:
 [1] ;  [2] ;  [1] ; ORCiD logo [1]
  1. The Arctic University of Norway, Tromso (Norway)
  2. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Advanced Light Source (ALS)
Publication Date:
Grant/Contract Number:
AC02-05CH11231
Type:
Accepted Manuscript
Journal Name:
Angewandte Chemie (International Edition)
Additional Journal Information:
Journal Name: Angewandte Chemie (International Edition); Journal Volume: 56; Journal Issue: 34; Journal ID: ISSN 1433-7851
Publisher:
Wiley
Research Org:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
OSTI Identifier:
1436613

Thomas, Kolle E., McCormick, Laura J., Vazquez-Lima, Hugo, and Ghosh, Abhik. Stabilization and Structure of the cis Tautomer of a Free-Base Porphyrin. United States: N. p., Web. doi:10.1002/anie.201701965.
Thomas, Kolle E., McCormick, Laura J., Vazquez-Lima, Hugo, & Ghosh, Abhik. Stabilization and Structure of the cis Tautomer of a Free-Base Porphyrin. United States. doi:10.1002/anie.201701965.
Thomas, Kolle E., McCormick, Laura J., Vazquez-Lima, Hugo, and Ghosh, Abhik. 2017. "Stabilization and Structure of the cis Tautomer of a Free-Base Porphyrin". United States. doi:10.1002/anie.201701965. https://www.osti.gov/servlets/purl/1436613.
@article{osti_1436613,
title = {Stabilization and Structure of the cis Tautomer of a Free-Base Porphyrin},
author = {Thomas, Kolle E. and McCormick, Laura J. and Vazquez-Lima, Hugo and Ghosh, Abhik},
abstractNote = {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]∙2H2O and cognate structures may act as supramolecular synthons, which, given their chirality, may even be amenable to resolution into optically pure enantiomers.},
doi = {10.1002/anie.201701965},
journal = {Angewandte Chemie (International Edition)},
number = 34,
volume = 56,
place = {United States},
year = {2017},
month = {3}
}

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