期刊
CHEMISTRY-A EUROPEAN JOURNAL
卷 27, 期 1, 页码 331-339出版社
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.202003414
关键词
atropisomers; crystallography; NMR; porphyrinoids; supramolecular chemistry
资金
- Technical University of Munich-Institute for Advanced Study
- European Union [764837]
- Irish Research Council [GOIPG 2017/1172]
- Science Foundation Ireland [IvP 13/IA/1894]
- Irish Research Council (IRC) [GOIPG/2017/1172] Funding Source: Irish Research Council (IRC)
This study sheds light on the fundamental issue of atropisomerism in porphyrins, using benzenesulfonic acid for host-guest interactions and NMR spectroscopy to characterize all four rotamers. The research suggests that charge-assisted complexation is key to unraveling the atropisomeric enigma in porphyrinoids. Additionally, X-ray structural analysis was used to investigate weak host-guest interactions in nonplanar porphyrins.
Atropisomerism is a fundamental feature of substituted biaryls resulting from rotation around the biaryl axis. Different stereoisomers are formed due to restricted rotation about the single bond, a situation often found in substituted porphyrins. Previously NMR determination of porphyrin atropisomers proved difficult, if not almost impossible to accomplish, due to low resolution or unresolvable resonance signals that predominantly overlapped. Here, we shed some light on this fundamental issue found in porphyrinoid stereochemistry. Using benzenesulfonic acid (BSA) for host-guest interactions and performing 1D, 2D NMR spectroscopic analyses, we were able to characterize all four rotamers of the nonplanar 5,10,15,20-tetrakis(2-aminophenyl)-2,3,7,8,12,13,17,18-octaethylporphyirin as restricted H-bonding complexes. Additionally, X-ray structural analysis was used to investigate aspects of the weak host-guest interactions. A detailed assignment of the chemical signals suggests charge-assisted complexation as a key to unravel the atropisomeric enigma. From a method development perspective, symmetry operations unique to porphyrin atropisomers offer an essential handle to accurately identify the rotamers using NMR techniques only.
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