A new stable perfluoroalkyl radical

Conclusions The radiolysis of perfluoro-4-methyl-2-pentene gives a stable radical whose ESR spectrum corresponds to (CF₃)₂CFFCF(CF₃)₂.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1667–1669, July, 1985.The authors express their gratitude to Yu. L. Bakhmutov for assistance in this work.     

A stable aminothioketyl radical in the gas phase

We report the first preparation of a stable aminothioketyl radical, CH(3)C(?)(SH)NHCH(3) (1), by fast electron transfer to protonated thioacetamide in the gas phase. The radical was characterized by neutralization-reionization mass spectrometry and ab initio calculations at high levels of theory. The unimolecular dissociations of 1 were elucidated with deuterium-labeled radicals CH(3)C(?)(SD)NHCH(3) (1a), CH(3)C(?)(SH)NDCH(3) (1b), CH(3)C(?)(SH)NHCD(3) (1c), and CD(3)C(?)(SH)NHCH(3) (1d). The main dissociations of 1 were a highly specific loss of the thiol H atom and a specific loss of the N-methyl group, which were competitive on the potential energy surface of the ground electronic state of the radical. RRKM calculations on the CCSD(T)/aug-cc-pVTZ potential energy surface indicated that the cleavage of the S-H bond in 1 dominated at low internal energies, E(int) < 232 kJ mol(-1). The cleavage of the N-CH(3) bond was calculated to prevail at higher internal energies. Loss of the thiol hydrogen atom can be further enhanced by dissociations originating from the B excited state of 1 when accessed by vertical electron transfer. Hydrogen atom addition to the thioamide sulfur atom is calculated to have an extremely low activation energy that may enable the thioamide group to function as a hydrogen atom trap in peptide radicals. The electronic properties and reactivity of the simple aminothioketyl radical reported here may be extrapolated and applied to elucidate the chemistry of thioxopeptide radicals and cation radicals of interest to protein structure studies.     

Fullerenols revisited as stable radical anions

The first exhaustive purification and characterization of the much-studied "fullerenols", prepared by reaction of C(60) in toluene with an oxygenated, aqueous NaOH solution using tetrabutylammonium hydroxide as a phase transfer catalyst, has been performed. The resulting fullerenol is not simply polyhydroxylated C(60) but rather is a structurally and electronically complex C(60) radical anion with a molecular formula of Na(+)(n)[C(60)O(x)(OH)(y)](n)(-) (where n = 2-3, x = 7-9, and y = 12-15) for three different, but identical, preparations. Surprisingly, Na(+)-fullerenol is paramagnetic, exhibiting mu(B) values in aqueous solution of 1.9-2.1 B.M. at 0.5 T and 300 K and R(1) proton relaxivities of 0.55-0.77 mM(-1)s(-1) at 20 MHz and 40 degrees C, values both slightly higher than those expected for a pure S = 1/2 spin system. ESR studies (ESE-FS and 2D nutation) of frozen aqueous solutions at 1.5 and 5.0 K establish that Na(+)-fullerenol is mainly S = 1/2 with a minor, but significant, component of S = 1. Thus, this is the first report to characterize these widely studied, water-soluble fullerenols as stable radical anions. The stability of the S = 1/2 Na(+)-fullerenol radical is likely due to a highly derivatized C(60) surface that protects a cyclopentadienyl radical center on the fullerene.     

Molecular recognition in a uradinyl-functionalized stable radical

Stable radical 2-(6-uradinyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-1-oxyl (1) binds to hydrogen-bonding complement 2,6-di(propylamido)pyridine (DAP) in chloroform with Ka=220 M(-1) at 33 degrees C; ESI-MS shows not only 1:DAP complementary dyad formation, but also 1:(DAP)2 formation at higher concentrations of DAP.     

A stable radical-substituted radical cation with strongly ferromagnetic interaction: nitronyl nitroxide-substituted 5,10-diphenyl-5,10-dihydrophenazine radical cation

A stable radical-substituted radical ion with strongly ferromagnetic intramolecular interaction (J) between the radical and radical ion sites is an attractive spin building block of organic magnets. We prepared 2-nitronyl nitroxide-substituted 5,10-diphenyl-5,10-dihydrophenazine radical cation, 1+. The 1+ salt was stable under aerated conditions at room temperature and had a large J/kB value (>/=+700 K).     

Tin-centered radical and cation: stable and free

The first stable stannyl radical (tBu2MeSi)3Sn* (1) has been synthesized by the reaction of tBu2MeSiNa with SnCl2-dioxane in diethyl ether. The X-ray crystal structure and electron paramagnetic resonance (EPR) data of this radical show that 1 has a planar geometry, being a pi-radical in both the solid and the liquid states. One-electron oxidation of 1 with Ph3C+.B(C6F5)4- in benzene quantitatively produced the corresponding cation (tBu2MeSi)3Sn+.B(C6F5)4- (2), representing the stable free stannylium ion that has been fully characterized by X-ray analysis and NMR data. Being free, 2 features a record downfield shifted resonance for stannylium ions: +2653 ppm.     

Investigation of the macromolecular stable free nitroxide radical

Polystyrene containing t-butyl nitroxide groups was prepared via polymer-analogous reactions and characterized by ESR measurements. Polymerizations of MMA and styrene initiated by AIBN at 50° have been investigated in the presence of the polymeric radical samples. A definite inhibiting effect was observed without retardation of the polymerization of either monomer. A linear relationship was found between the concentration of the polymeric inhibitor and the inhibition period.     

Deuterated N-difluoromethylthiophthalimide: A stable,scalable reagent for radical and electrophilic deuteriodifluoromethylthiolations

A new, stable and scalable reagent for deuteriodifluoromethylthiolation (deuterated N-difluoromethylthiophthalimide, PhthSCF₂D) has been developed. This reagent can be applied for the photocatalytic radical deuteriodifluoromethylthiolation of various olefins and aldehydes (30 examples). Meanwhile, it can achieve the electrophilic deuteriodifluoromethylthiolation of a series of electrophilic substrates including electron-rich arenes, aryl/vinylboronicacids, alkynes, amines, thiols and β-ketoesters (22 examples). Some complex molecules can also be applied in both radical and electrophilic deuteriodifluoromethylthiolation using PhthSCF₂D as the reagent.     

Addition of stable nitroxide radical to stable divalent compounds of heavier group 14 elements

The reactions of stable cyclic dialkylgermylene 2 and dialkylstannylene 3 with 2,2,6,6-tetramethylpiperidinyl-1-oxy (TEMPO) radical (2 equiv) gave the corresponding 1:2 adducts 4 and 5, respectively, which were characterized by NMR, MS, and X-ray analyses. The kinetics of the stepwise addition of two TEMPO molecules to germylene 2 revealed that the initial addition of TEMPO to 2 was 1010 times slower than the second TEMPO addition to the resulting germyl radical. The origin of the rate difference was discussed on the basis of the qualitative perturbation theory. In contrast to the reactions of 2 and 3, the reaction of dialkylsilylene 1 with TEMPO gave an interesting 1,3-dioxadisiletane derivative.     

Complex macromolecular structures from stable radical containing block copolymers

A novel synthetic strategy for the synthesis of graft copolymers is reported. Block copolymers containing segments with stable nitroxyl radicals side groups were first prepared by anionic polymerization, which were then used as a precursor for the subsequent nitroxide-mediated radical polymerization (NMRP) of styrene. This way, block–graft copolymers with polystyrene side chains grafted from one of the blocks were successfully synthesized in a controlled manner. In addition, block–graft copolymers with grafted polystyrene chains and a poly(tert-butyl methacrylate) block were subjected to hydrolysis to yield the corresponding amphiphilic polymers. The structures and the molecular weight characteristics of the polymers were characterized by spectral and chromatographic analyses. The surface morphology of thus obtained polymers was also investigated by microscopic techniques. © 2019 Wiley Periodicals, Inc. J. Polym. Sci. 2020 , 58, 62–69     

Mechanically compliant single crystals of a stable organic radical

Mechanically compliant organic crystals are the foundation of the development of future flexible, light-weight single-crystal electronics, and this requires reversibly deformable crystalline organic materials with permanent magnetism. Here, we report and characterize the first instance of a plastically bendable single crystal of a permanent organic radical, 4-(4′-cyano-2′,3′,4′,5′-tetrafluorophenyl)-1,2,3,5-dithiadiazolyl. The weak interactions between the radicals render single crystals of the β phase of this material exceedingly soft, and the S–N interactions facilitate plastic bending. EPR imaging of a bent single crystal reveals the effect of deformation on the three-dimensional spin density of the crystal. The unusual mechanical compliance of this material opens prospects for exploration into flexible crystals of other stable organic radicals towards the development of flexible light-weight organic magnetoresistance devices based on weak, non-hydrogen-bonded interactions in molecular crystals.

Mechanically soft crystals are interesting candidates for single crystal electronics. Here, crystals of a stable dithiadiazolyl radical are shown to be plastically bendable and display a change in their spin density in response to mechanical force.     

Synthesis of diblock copolymers by combining stable free radical polymerization and atom transfer radical polymerization

A stable nitroxyl radical functionalized with an initiating group for atom transfer radical polymerization (ATRP), 4‐(2‐bromo‐2‐methylpropionyloxy)‐2,2,6,6‐tetramethyl‐1‐piperidinyloxy (Br‐TEMPO), was synthesized by the reaction of 4‐hydroxyl‐2,2,6,6‐tetramethyl‐1‐piperidinyloxy with 2‐bromo‐2‐methylpropionyl bromide. Stable free radical polymerization of styrene was then carried out using a conventional thermal initiator, dibenzoyl peroxide, along with Br‐TEMPO. The obtained polystyrene had an active bromine atom for ATRP at the ω‐end of the chain and was used as the macroinitiator for ATRP of methyl acrylate and ethyl acrylate to prepare block copolymers. The molecular weights of the resulting block copolymers at different monomer conversions shifted to higher molecular weights and increased with monomer conversion. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2468–2475, 2006     

Synthesis and radical polymerization of hydrolytically stable dentin bonding agents

Acrylic groups containing phosphonic acids were synthesized by ether formation of ethyl α‐chloromethylacrylate with hydroxyalkyl phosphonates and subsequent hydrolysis to the corresponding phosphonic acid α‐methylsubstituted acrylates. Furthermore, phosphonic acids derived from acrylonitrile and acrylamide were synthesized. The monomers are hydrolytically stable in aqueous ethanol. The radical polymerization of the monofunctional phosphonic acids results in water soluble polymers, whereas in case of a phosphonic acid diacrylate a cross‐linked polymer was formed. The most radical polymerizable phosphonic acids can be used to promote the adhesion to dentin.     

Characterization of a stable ruthenium complex with an oxyl radical

The ruthenium oxyl radical complex, [Ru(II)(trpy)(Bu(2)SQ)O(.-)] (trpy = 2,2':6',2"-terpyridine, Bu(2)SQ = 3,5-di-tert-butyl-1,2-benzosemiquinone) was prepared for the first time by the double deprotonation of the aqua ligand of [Ru(III)(trpy)(Bu(2)SQ)(OH(2))](ClO(4))(2). [Ru(III)(trpy)(Bu(2)SQ)(OH(2))](ClO(4))(2) is reversibly converted to [Ru(III)(trpy)(Bu(2)SQ)(OH-)](+) upon dissociation of the aqua proton (pK(a) 5.5). Deprotonation of the hydroxo proton gave rise to intramolecular electron transfer from the resultant O(2-) to Ru-dioxolene. The resultant [Ru(II)(trpy)(Bu(2)SQ)O(.-)] showed antiferromagnetic behavior with a Ru(II)-semiquinone moiety and oxyl radical, the latter of which was characterized by a spin trapping technique. The most characteristic structural feature of [Ru(II)(trpy)(Bu(2)SQ)O(.-)] is a long Ru-O bond length (2.042(6) A) as the first terminal metal-O bond with a single bond length. To elucidate the substituent effect of a quinone ligand, [Ru(III)(trpy)(4ClSQ)(OH(2))](ClO(4))(2) (4ClSQ = 4-chloro-1,2-benzosemiquinone) was prepared and we compared the deprotonation behavior of the aqua ligand with that of [Ru(III)(trpy)(Bu(2)SQ)(OH(2))](ClO(4))(2). Deprotonation of the aqua ligand of [Ru(III)(trpy)(4ClSQ)(OH(2))](ClO(4))(2) induced intramolecular electron transfer from OH- to the [Ru(III)(4ClSQ)] moiety affording [Ru(II)(trpy)(4ClSQ)(OH.)]+, which then probably changed to [Ru(II)(trpy)(4ClSQ)O(.-)]. The antiferromagnetic interactions (J values) between Ru(II)-semiquinone and the oxyl radical for [Ru(II)(trpy)(Bu(2)SQ)O(.-)] and for [Ru(II)(trpy)(4ClSQ)O(.-)] were 2J = -0.67 cm(-1) and -1.97 cm(-1), respectively.