Stabilization and Structure of the cis Tautomer of a Free-Base Porphyrin
Journal Article
·
· Angewandte Chemie (International Edition)
- The Arctic University of Norway, Tromso (Norway)
- Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Advanced Light Source (ALS)
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.
- Research Organization:
- Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
- Grant/Contract Number:
- AC02-05CH11231
- OSTI ID:
- 1436613
- Journal Information:
- Angewandte Chemie (International Edition), Journal Name: Angewandte Chemie (International Edition) Journal Issue: 34 Vol. 56; ISSN 1433-7851
- Publisher:
- WileyCopyright Statement
- Country of Publication:
- United States
- Language:
- English
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