Bis-Spiro-Oxetane and Bis-Spiro-Tetrahydrofuran Pyrroline Nitroxide Radicals: Synthesis and Electron Spin Relaxation Studies

Huang, Sheng‐Dian; Pink, Maren; Ngendahimana, Thacien; Rajca, Suchada; Eaton, Gareth R.; Rajca, Andrzej

doi:10.1021/acs.joc.1c01670

Cited by 9 publications

(8 citation statements)

References 47 publications

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“…Such effects have been observed in a variety of other methyl-containing systems. [55][56][57][58] The decrease of the stretch exponent at low temperatures corroborates this interpretation. S5, SI.…”

Section: Resultssupporting

confidence: 69%

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Thermally Ultra-Robust S = ½ Tetrazolinyl Radicals: Synthesis, Electronic Structure, Magnetism, and Nanoneedle Assemblies on Silicon Surface.

Yang

Pink

Nowik-Boltyk

et al. 2023

Preprint

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Open-shell organic molecules, including S = ½ radicals, may provide enhanced properties for several emerging technologies, however, relatively few synthesized to date possess robust thermal stability and processability. We report synthesis of S = ½ biphenylene-fused tetrazolinyl radicals 1 and 2. Both radicals possess near-perfect planar structures based on their X-ray structures and DFT computations. Radical 1 possesses an outstanding thermal stability as indicated by the onset of decomposition at 269 °C, based on thermogravimetric analysis (TGA) data. Both radicals possess very low oxidation potentials < 0 V (vs. SCE) and their electrochemical energy gaps, Ecell 0.9 eV, are rather low. Magnetic properties of polycrystalline 1 are characterized by SQUID magnetometry revealing a one-dimensional S = ½ antiferromagnetic Heisenberg chain with exchange coupling constant J’/k –22.0 K. Radical 1 in toluene glass possesses a long electron spin coherence time, Tm ≈ 7 μs in the 40 – 80 K temperature range, a property advantageous for potential applications as a molecular spin qubit. Radical 1 is evaporated under ultrahigh vacuum (UHV) forming assemblies of intact radicals on a silicon substrate, as confirmed by high-resolution X-ray photoelectron spectroscopy (XPS). Scanning electron microscope (SEM) images indicate that the radical molecules form nanoneedles on the substrate. The nanoneedles are stable for at least 64 hours under air as monitored by using X-ray photoelectron spectroscopy. EPR studies of the thicker assemblies, prepared by UHV evaporation, indicate radical decay according to first-order kinetics with a long half-life of 50 +/-4 days at ambient conditions.

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Section: Resultssupporting

confidence: 69%

“…4 and 4 -5 s in the 40 -80 K range for typical gem-dimethyl and optimized spirocyclic pyrroline nitroxide radicals, respectively,58 or Tm = 4 -6 s and Tm < 4 s in the 40 -80 K range for Blatter radicals immobilized on silica and optimized vanadium complexes in protiated solvents/matrices, respectively 12,59,60. SQUID magnetometry.…”

mentioning

confidence: 99%

Thermally Ultra-Robust S = ½ Tetrazolinyl Radicals: Synthesis, Electronic Structure, Magnetism, and Nanoneedle Assemblies on Silicon Surface.

Yang

Pink

Nowik-Boltyk

et al. 2023

Preprint

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“…Protons on these methyl groups are responsible for enhancing decoherence. Such effects have been observed in a variety of other methyl-containing systems. − The decrease of the stretch exponent at low temperatures corroborates this interpretation.…”

Section: Resultsmentioning

confidence: 99%

“…One of the key prerequisites for the use of paramagnetic molecules as spin qubits for potential quantum sensing applications is a long coherence time T m . , For 1 in toluene- h 8 , the value of T m ≈ 7 μs in the 40–80 K temperature range is comparable to T m = 7.2 μs for a Blatter radical derivative measured in toluene- d 8 at 25 K . The value of T m ≈ 7 μs is significantly longer than T m = 3–4 and 4–5 μs in the 40–80 K range for typical gem -dimethyl and optimized spirocyclic pyrroline nitroxide radicals, respectively, or T m = 4–6 μs and T m < 4 μs in the 40–80 K range for Blatter radicals immobilized on silica and optimized vanadium complexes in protiated solvents/matrices, respectively. ,, …”

Section: Resultsmentioning

confidence: 99%

Thermally Ultrarobust S = 1/2 Tetrazolinyl Radicals: Synthesis, Electronic Structure, Magnetism, and Nanoneedle Assemblies on Silicon Surface

et al. 2023

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Open-shell organic molecules, including S = 1/2 radicals, may provide enhanced properties for several emerging technologies; however, relatively few synthesized to date possess robust thermal stability and processability. We report the synthesis of S = 1/2 biphenylene-fused tetrazolinyl radicals 1 and 2. Both radicals possess near-perfect planar structures based on their X-ray structures and density-functional theory (DFT) computations. Radical 1 possesses outstanding thermal stability as indicated by the onset of decomposition at 269 °C, based on thermogravimetric analysis (TGA) data. Both radicals possess very low oxidation potentials <0 V (vs. SCE) and their electrochemical energy gaps, E cell ≈ 0.9 eV, are rather low. Magnetic properties of polycrystalline 1 are characterized by superconducting quantum interference device (SQUID) magnetometry revealing a one-dimensional S = 1/2 antiferromagnetic Heisenberg chain with exchange coupling constant J′/k ≈ −22.0 K. Radical 1 in toluene glass possesses a long electron spin coherence time, T m ≈ 7 μs in the 40–80 K temperature range, a property advantageous for potential applications as a molecular spin qubit. Radical 1 is evaporated under ultrahigh vacuum (UHV) forming assemblies of intact radicals on a silicon substrate, as confirmed by high-resolution X-ray photoelectron spectroscopy (XPS). Scanning electron microscope (SEM) images indicate that the radical molecules form nanoneedles on the substrate. The nanoneedles are stable for at least 64 hours under air as monitored by using X-ray photoelectron spectroscopy. Electron paramagnetic resonance (EPR) studies of the thicker assemblies, prepared by UHV evaporation, indicate radical decay according to first-order kinetics with a long half-life of 50 ± 4 days at ambient conditions.

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“…Spirocyclic nitroxides such as 12 , , which also belong to the sterically highly hindered N -oxyl radicals, have been prepared. The steric shielding in such spiro systems can be further increased through conformational fixation, as shown for the menthone-derived nitroxide 13 . , Other spirocyclic compounds are known, , and the bis-spiro oxetane 14 is in our eyes an interesting member of this family …”

Section: Preparation Of Nitroxides and Selected Derivativesmentioning

confidence: 92%

Organic Synthesis Using Nitroxides

Leifert

Studer

2023

Chem. Rev.

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Nitroxides, also known as nitroxyl radicals, are long-lived or stable radicals with the general structure R 1 R 2 N−O • . The spin distribution over the nitroxide N and O atoms contributes to the thermodynamic stability of these radicals. The presence of bulky N-substituents R 1 and R 2 prevents nitroxide radical dimerization, ensuring their kinetic stability. Despite their reactivity toward various transient C radicals, some nitroxides can be easily stored under air at room temperature. Furthermore, nitroxides can be oxidized to oxoammonium salts (R 1 R 2 N�O + ) or reduced to anions (R 1 R 2 N−O − ), enabling them to act as valuable oxidants or reductants depending on their oxidation state. Therefore, they exhibit interesting reactivity across all three oxidation states. Due to these fascinating properties, nitroxides find extensive applications in diverse fields such as biochemistry, medicinal chemistry, materials science, and organic synthesis. This review focuses on the versatile applications of nitroxides in organic synthesis. For their use in other important fields, we will refer to several review articles. The introductory part provides a brief overview of the history of nitroxide chemistry. Subsequently, the key methods for preparing nitroxides are discussed, followed by an examination of their structural diversity and physical properties. The main portion of this review is dedicated to oxidation reactions, wherein parent nitroxides or their corresponding oxoammonium salts serve as active species. It will be demonstrated that various functional groups (such as alcohols, amines, enolates, and alkanes among others) can be efficiently oxidized. These oxidations can be carried out using nitroxides as catalysts in combination with various stoichiometric terminal oxidants. By reducing nitroxides to their corresponding anions, they become effective reducing reagents with intriguing applications in organic synthesis. Nitroxides possess the ability to selectively react with transient radicals, making them useful for terminating radical cascade reactions by forming alkoxyamines. Depending on their structure, alkoxyamines exhibit weak C−O bonds, allowing for the thermal generation of C radicals through reversible C−O bond cleavage. Such thermally generated C radicals can participate in various radical transformations, as discussed toward the end of this review. Furthermore, the application of this strategy in natural product synthesis will be presented.

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Bis-Spiro-Oxetane and Bis-Spiro-Tetrahydrofuran Pyrroline Nitroxide Radicals: Synthesis and Electron Spin Relaxation Studies

Cited by 9 publications

References 47 publications

Thermally Ultra-Robust S = ½ Tetrazolinyl Radicals: Synthesis, Electronic Structure, Magnetism, and Nanoneedle Assemblies on Silicon Surface.

Thermally Ultra-Robust S = ½ Tetrazolinyl Radicals: Synthesis, Electronic Structure, Magnetism, and Nanoneedle Assemblies on Silicon Surface.

Thermally Ultrarobust S = 1/2 Tetrazolinyl Radicals: Synthesis, Electronic Structure, Magnetism, and Nanoneedle Assemblies on Silicon Surface

Organic Synthesis Using Nitroxides

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