Spirocyclic Nitroxide Biradicals: Synthesis and Evaluation as Dynamic Nuclear Polarizing Agents

A method for the synthesis of rigid nitroxide biradicals with various spatial orientations between the radical centers is reported. Diketones were employed as substrates for tin amine protocol (SnAP) reagents to provide the parent spirocyclic diamines. Oxidation by peroxyacids provided the correspon...

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Bibliographic Details
Published in:Helvetica chimica acta 2020-12, Vol.103 (12), p.n/a
Main Authors: Jackl, Moritz K., Gordon, Christopher P., Copéret, Christophe, Bode, Jeffrey W.
Format: Article
Language:English
Subjects:
Angles (geometry)
biradicals
Crystallography
Diamines
Diketones
DNP
EPR
Nitroxide
Oxidation
Polarization
Reagents
SnAP
Spatial distribution
Spectroscopy
spiro compounds
Substrates
Synthesis
Tin
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Summary:A method for the synthesis of rigid nitroxide biradicals with various spatial orientations between the radical centers is reported. Diketones were employed as substrates for tin amine protocol (SnAP) reagents to provide the parent spirocyclic diamines. Oxidation by peroxyacids provided the corresponding nitroxide biradicals. A set of four different biradicals with various interelectron distances and torsion angles between the radical planes was synthesized using this method. The exact geometries were determined by X‐ray crystallography and the biradicals were investigated by EPR spectroscopy and evaluated for their dynamic nuclear polarization (DNP) performance. 1H‐DNP enhancements in the range of 1.2–2.1 at 14.1 Tesla (600 MHz spectrometer) were achieved. This synthetic methodology opens a promising alternative to access nitroxide biradicals with various torsional angles and inter radical distances.
ISSN:0018-019X
1522-2675
DOI:10.1002/hlca.202000179