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Atsuhiro Osuka - One of the best experts on this subject based on the ideXlab platform.
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coordination induced spin state switching of an Aminyl radical bridged nickel ii porphyrin dimer between doublet and sextet states
Angewandte Chemie, 2019Co-Authors: Daiki Shimizu, Yuki Ide, Takahisa Ikeue, Atsuhiro OsukaAbstract:A bis(NiII -porphyrinyl)Aminyl radical with meso-C6 F5 groups was prepared as a spin-delocalized stable Aminyl radical with a doublet spin state. Upon addition of pyridine, both NiII centers became hexacoordinated by accepting two axial pyridines, which triggered a spin-state change of the NiII centers from diamagnetic (S=0) to paramagnetic (S=1). The resulting high-spin NiII centers interact with the Aminyl radical ferromagnetically to give rise to an overall sextet state (S=5/2). Importantly, this coordination-induced spin-state switching can be conducted in a reversible manner, in that washing of the high-spin radical with aqueous hydrochloric acid regenerates the original doublet radical in good yield.
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Coordination‐Induced Spin‐State Switching of an Aminyl‐Radical‐Bridged Nickel(II) Porphyrin Dimer between Doublet and Sextet States
Angewandte Chemie (International ed. in English), 2019Co-Authors: Daiki Shimizu, Yuki Ide, Takahisa Ikeue, Atsuhiro OsukaAbstract:A bis(NiII -porphyrinyl)Aminyl radical with meso-C6 F5 groups was prepared as a spin-delocalized stable Aminyl radical with a doublet spin state. Upon addition of pyridine, both NiII centers became hexacoordinated by accepting two axial pyridines, which triggered a spin-state change of the NiII centers from diamagnetic (S=0) to paramagnetic (S=1). The resulting high-spin NiII centers interact with the Aminyl radical ferromagnetically to give rise to an overall sextet state (S=5/2). Importantly, this coordination-induced spin-state switching can be conducted in a reversible manner, in that washing of the high-spin radical with aqueous hydrochloric acid regenerates the original doublet radical in good yield.
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stable subporphyrin meso Aminyl radicals without resonance stabilization by a neighboring heteroatom
Angewandte Chemie, 2017Co-Authors: Daiki Shimizu, Ko Furukawa, Atsuhiro OsukaAbstract:Most Aminyl radicals studied so far are resonance-stabilized by neighboring heteroatoms, and those without such stabilization are usually short-lived. We report herein that subporphyrin meso-2,4,6-trichlorophenylAminyl radicals and a bis(5-subporphyrinyl)Aminyl radical are fairly stable under ambient conditions without such stabilization. The subporphyrin meso-2,4,6-trichlorophenylAminyl radical crystal structure displays a characteristically short Cmeso -N bond and a perpendicular arrangement of the meso-arylamino group. The stabilities of these radicals have been ascribed to extensive spin delocalization over the subporphyrin π-electronic network as well as steric protection around the Aminyl radical center.
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Stable Subporphyrin meso‐Aminyl Radicals without Resonance Stabilization by a Neighboring Heteroatom
Angewandte Chemie (International ed. in English), 2017Co-Authors: Daiki Shimizu, Ko Furukawa, Atsuhiro OsukaAbstract:Most Aminyl radicals studied so far are resonance-stabilized by neighboring heteroatoms, and those without such stabilization are usually short-lived. We report herein that subporphyrin meso-2,4,6-trichlorophenylAminyl radicals and a bis(5-subporphyrinyl)Aminyl radical are fairly stable under ambient conditions without such stabilization. The subporphyrin meso-2,4,6-trichlorophenylAminyl radical crystal structure displays a characteristically short Cmeso -N bond and a perpendicular arrangement of the meso-arylamino group. The stabilities of these radicals have been ascribed to extensive spin delocalization over the subporphyrin π-electronic network as well as steric protection around the Aminyl radical center.
Daiki Shimizu - One of the best experts on this subject based on the ideXlab platform.
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coordination induced spin state switching of an Aminyl radical bridged nickel ii porphyrin dimer between doublet and sextet states
Angewandte Chemie, 2019Co-Authors: Daiki Shimizu, Yuki Ide, Takahisa Ikeue, Atsuhiro OsukaAbstract:A bis(NiII -porphyrinyl)Aminyl radical with meso-C6 F5 groups was prepared as a spin-delocalized stable Aminyl radical with a doublet spin state. Upon addition of pyridine, both NiII centers became hexacoordinated by accepting two axial pyridines, which triggered a spin-state change of the NiII centers from diamagnetic (S=0) to paramagnetic (S=1). The resulting high-spin NiII centers interact with the Aminyl radical ferromagnetically to give rise to an overall sextet state (S=5/2). Importantly, this coordination-induced spin-state switching can be conducted in a reversible manner, in that washing of the high-spin radical with aqueous hydrochloric acid regenerates the original doublet radical in good yield.
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Coordination‐Induced Spin‐State Switching of an Aminyl‐Radical‐Bridged Nickel(II) Porphyrin Dimer between Doublet and Sextet States
Angewandte Chemie (International ed. in English), 2019Co-Authors: Daiki Shimizu, Yuki Ide, Takahisa Ikeue, Atsuhiro OsukaAbstract:A bis(NiII -porphyrinyl)Aminyl radical with meso-C6 F5 groups was prepared as a spin-delocalized stable Aminyl radical with a doublet spin state. Upon addition of pyridine, both NiII centers became hexacoordinated by accepting two axial pyridines, which triggered a spin-state change of the NiII centers from diamagnetic (S=0) to paramagnetic (S=1). The resulting high-spin NiII centers interact with the Aminyl radical ferromagnetically to give rise to an overall sextet state (S=5/2). Importantly, this coordination-induced spin-state switching can be conducted in a reversible manner, in that washing of the high-spin radical with aqueous hydrochloric acid regenerates the original doublet radical in good yield.
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stable subporphyrin meso Aminyl radicals without resonance stabilization by a neighboring heteroatom
Angewandte Chemie, 2017Co-Authors: Daiki Shimizu, Ko Furukawa, Atsuhiro OsukaAbstract:Most Aminyl radicals studied so far are resonance-stabilized by neighboring heteroatoms, and those without such stabilization are usually short-lived. We report herein that subporphyrin meso-2,4,6-trichlorophenylAminyl radicals and a bis(5-subporphyrinyl)Aminyl radical are fairly stable under ambient conditions without such stabilization. The subporphyrin meso-2,4,6-trichlorophenylAminyl radical crystal structure displays a characteristically short Cmeso -N bond and a perpendicular arrangement of the meso-arylamino group. The stabilities of these radicals have been ascribed to extensive spin delocalization over the subporphyrin π-electronic network as well as steric protection around the Aminyl radical center.
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Stable Subporphyrin meso‐Aminyl Radicals without Resonance Stabilization by a Neighboring Heteroatom
Angewandte Chemie (International ed. in English), 2017Co-Authors: Daiki Shimizu, Ko Furukawa, Atsuhiro OsukaAbstract:Most Aminyl radicals studied so far are resonance-stabilized by neighboring heteroatoms, and those without such stabilization are usually short-lived. We report herein that subporphyrin meso-2,4,6-trichlorophenylAminyl radicals and a bis(5-subporphyrinyl)Aminyl radical are fairly stable under ambient conditions without such stabilization. The subporphyrin meso-2,4,6-trichlorophenylAminyl radical crystal structure displays a characteristically short Cmeso -N bond and a perpendicular arrangement of the meso-arylamino group. The stabilities of these radicals have been ascribed to extensive spin delocalization over the subporphyrin π-electronic network as well as steric protection around the Aminyl radical center.
Suchada Rajca - One of the best experts on this subject based on the ideXlab platform.
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PEGylated, Water-Soluble, Stable Aminyl Radical
2017Co-Authors: Ying Wang, Suchada Rajca, Andrzej RajcaAbstract:We report the synthesis and kinetic study of PEGylated, water-soluble Aminyl radical 2. The radical possesses four mPEG-3 groups replacing four methyl groups in the tert-butyl groups at the 3- and 6-positions of 1,3,6,8-tetra-tert-butyl carbazyl (TTBC). This structure is designed to mitigate the rapid decomposition of the radical via intramolecular 1,5-hydrogen atom transfer (1,5-HAT) that was observed in its constitutional isomer 1-H with four mPEG-3 groups in the vicinity of the nitrogen-centered radical (1- and 8-positions of TTBC). In dry, degassed acetone at 295 K, the radical 2 has a half-life, τ1/2 = 49 h (ΔH‡ = 17.9 ± 0.8 kcal mol–1), which is 3 orders of magnitude longer than that for 1-H, which decays via 1,5-HAT (τ1/2 = 48 s, ΔH‡ = 10.0 ± 0.3 kcal mol–1). Aminyl radical 2 aggregates at ambient conditions in water and has a half-life, τ1/2 = 2 h
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Aza-m-Xylylene Diradical with Increased Steric Protection of the Aminyl Radicals
The Journal of organic chemistry, 2015Co-Authors: Arnon Olankitwanit, Suchada Rajca, Andrzej RajcaAbstract:Aminyl diradical 3, a derivative of aza-m-xylylene, is expected to be more stable than diradical 1, due to increased steric protection of the radicals by additional methyl groups in the pendant group. Here we report synthesis and characterization of diradical 3. The structure of diamine precursor 6 is characterized by high-field 1H NMR spectroscopy in which the two diastereomers (meso and ± pair) are distinguishable. In addition, correlation between the DFT-calculated and experimental 1H and 13C NMR chemical shifts provides evidence in support of the diamine structure. Electrochemistry of the diamine is carried out to explore redox properties and stability of the corresponding aminium diradical dications. The ground state and ΔEST for 3 are established by statistical analyses of mean χT determined by EPR spectroscopy. Decay kinetics of Aminyl diradical 3 indicates that the decay of 3 is faster than that of 1, possibly due to intramolecular hydrogen atom abstraction from benzylic methyl groups in 3, follow...
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triplet s 1 ground state Aminyl diradical
Journal of the American Chemical Society, 2007Co-Authors: Andrzej Rajca, Maren Pink, Kouichi Shiraishi, Suchada RajcaAbstract:Aminyl diradical, which is stable in solution at low temperatures, is prepared. EPR spectra and SQUID magnetometry indicate that the diradical is planar and it possesses triplet ground state, with strong ferromagnetic coupling.
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Triplet (S = 1) Ground State Aminyl Diradical
Journal of the American Chemical Society, 2007Co-Authors: Andrzej Rajca, Maren Pink, Kouichi Shiraishi, Suchada RajcaAbstract:Aminyl diradical, which is stable in solution at low temperatures, is prepared. EPR spectra and SQUID magnetometry indicate that the diradical is planar and it possesses triplet ground state, with strong ferromagnetic coupling.
Andrzej Rajca - One of the best experts on this subject based on the ideXlab platform.
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PEGylated, Water-Soluble, Stable Aminyl Radical
2017Co-Authors: Ying Wang, Suchada Rajca, Andrzej RajcaAbstract:We report the synthesis and kinetic study of PEGylated, water-soluble Aminyl radical 2. The radical possesses four mPEG-3 groups replacing four methyl groups in the tert-butyl groups at the 3- and 6-positions of 1,3,6,8-tetra-tert-butyl carbazyl (TTBC). This structure is designed to mitigate the rapid decomposition of the radical via intramolecular 1,5-hydrogen atom transfer (1,5-HAT) that was observed in its constitutional isomer 1-H with four mPEG-3 groups in the vicinity of the nitrogen-centered radical (1- and 8-positions of TTBC). In dry, degassed acetone at 295 K, the radical 2 has a half-life, τ1/2 = 49 h (ΔH‡ = 17.9 ± 0.8 kcal mol–1), which is 3 orders of magnitude longer than that for 1-H, which decays via 1,5-HAT (τ1/2 = 48 s, ΔH‡ = 10.0 ± 0.3 kcal mol–1). Aminyl radical 2 aggregates at ambient conditions in water and has a half-life, τ1/2 = 2 h
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Aza-m-Xylylene Diradical with Increased Steric Protection of the Aminyl Radicals
The Journal of organic chemistry, 2015Co-Authors: Arnon Olankitwanit, Suchada Rajca, Andrzej RajcaAbstract:Aminyl diradical 3, a derivative of aza-m-xylylene, is expected to be more stable than diradical 1, due to increased steric protection of the radicals by additional methyl groups in the pendant group. Here we report synthesis and characterization of diradical 3. The structure of diamine precursor 6 is characterized by high-field 1H NMR spectroscopy in which the two diastereomers (meso and ± pair) are distinguishable. In addition, correlation between the DFT-calculated and experimental 1H and 13C NMR chemical shifts provides evidence in support of the diamine structure. Electrochemistry of the diamine is carried out to explore redox properties and stability of the corresponding aminium diradical dications. The ground state and ΔEST for 3 are established by statistical analyses of mean χT determined by EPR spectroscopy. Decay kinetics of Aminyl diradical 3 indicates that the decay of 3 is faster than that of 1, possibly due to intramolecular hydrogen atom abstraction from benzylic methyl groups in 3, follow...
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triplet s 1 ground state Aminyl diradical
Journal of the American Chemical Society, 2007Co-Authors: Andrzej Rajca, Maren Pink, Kouichi Shiraishi, Suchada RajcaAbstract:Aminyl diradical, which is stable in solution at low temperatures, is prepared. EPR spectra and SQUID magnetometry indicate that the diradical is planar and it possesses triplet ground state, with strong ferromagnetic coupling.
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Triplet (S = 1) Ground State Aminyl Diradical
Journal of the American Chemical Society, 2007Co-Authors: Andrzej Rajca, Maren Pink, Kouichi Shiraishi, Suchada RajcaAbstract:Aminyl diradical, which is stable in solution at low temperatures, is prepared. EPR spectra and SQUID magnetometry indicate that the diradical is planar and it possesses triplet ground state, with strong ferromagnetic coupling.
R. J. Marmon - One of the best experts on this subject based on the ideXlab platform.
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Synthesis of pyrrolizidines using Aminyl radicals generated from sulfenamide precursors
Tetrahedron, 1994Co-Authors: W. Russell Bowman, D. N. Clark, R. J. MarmonAbstract:Abstract Tandem radical cyclisations of Aminyl radicals generated from sulfenamide precursors have been used for the synthesis of pyrrolizidines and other polycyclic nitrogen heterocycles. The Aminyl radicals are generated by reaction between sulfenamide precursors and Bu3SnH.
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Generation of Aminyl radicals using sulfenamides as synthetic precursors
Tetrahedron, 1994Co-Authors: W. Russell Bowman, D. N. Clark, R. J. MarmonAbstract:Abstract Sulfenamides are synthesised from reaction between amines and N -(benzenesulfenyl)-phthalimide or benzenesulfenyl chloride. The sulfenamides undergo reaction with tributyltin hydride to yield Aminyl radicals which can be cyclised onto suitable alkenes.
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Cyclisation of Aminyl radicals using sulfenamide precursors
Tetrahedron Letters, 1992Co-Authors: W. Russell Bowman, D. N. Clark, R. J. MarmonAbstract:Abstract Sulfenamides react readily with tributyltin hydride to yield Aminyl radicals, which undergo intramolecular addition to activated double bonds.
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Sulphenamides as synthetic precursors of Aminyl radicals
Tetrahedron Letters, 1991Co-Authors: W. Russell Bowman, D. N. Clark, R. J. MarmonAbstract:Abstract Sulphenamides, readily synthesised from reaction between benzenesulphenyl derivatives and amines, undergo facile reaction with radical generating reagents such as tributyltin hydride to yield Aminyl radicals.