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

Journal Article · · Angewandte Chemie (International Edition)
 [1];  [2];  [1];  [1]
  1. The Arctic University of Norway, Tromso (Norway)
  2. 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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Cited By (8)

Molekulares Engineering freier Porphyrinbasen als Liganden - das N-H⋅⋅⋅X-Bindungsmotiv in Tetrapyrrolen journal November 2018
Molecular Engineering of Free-Base Porphyrins as Ligands-The N−H⋅⋅⋅X Binding Motif in Tetrapyrroles journal November 2018
Two Macrocycles in One Shot: Synthesis, Spectroscopy, Photophysics, and Tautomerism of 23-Oxahemiporphycene and 21-Oxacorrole-5-carbaldehyde journal June 2018
Incremental Introduction of Organocatalytic Activity into Conformationally Engineered Porphyrins: Incremental Introduction of Organocatalytic Activity into Conformationally Engineered Porphyrins journal February 2019
Porphyrins in troubled times: a spotlight on porphyrins and their metal complexes for explosives testing and CBRN defense journal January 2018
Multi-mode supermolecular polymerization driven by host–guest interactions journal January 2018
Positive shift in corrole redox potentials leveraged by modest β-CF 3 -substitution helps achieve efficient photocatalytic C–H bond functionalization by group 13 complexes journal January 2019
Free-base porphyrins with localized NH protons. Can substituents alone stabilize the elusive cis tautomer? journal January 2020


Figures / Tables (5)


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