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Thermally stable organic diradicals with a triplet ground state along with large singlet-triplet energy gap have significant potential for advanced technological applications. A series of phenylene-bridged diradicals with oxoverdazyl and nitronyl nitroxide units were synthesized via a palladium-catalyzed cross-coupling reaction of iodoverdazyls with a nitronyl nitroxide-2-ide gold(I) complex with high yields. The diradicals exhibit high stability and do not decompose in an inert atmosphere up to 180 °C. For the diradicals, both substantial AF (ΔEST ≈-64 cm-1 ) and FM (ΔEST ≥25 and 100 cm-1 ) intramolecular exchange interactions were observed. The sign of the exchange interaction is determined both by the bridging moiety (para- or meta-phenylene) and by the type of oxoverdazyl block (C-linked or N-linked). Upon crystallization, diradicals with the triplet ground state form unique one-dimensional exchange-coupled chains with strong intra- and weak inter-diradical ferromagnetic coupling.

Diethylaminovinyl derivatives of halogenated 1,4-quinones (enaminoquinones) are produced by the interaction of halogenated 1,4-quinones with N,N-diethyl-N-vinylamine obtained in situ from Et2NH and MeCHO. Molecular and crystal structures of enaminoquinones halogenated in the quinone fragment are determined. It is shown that in the solid phase, atoms of the entire push-pull system of enaminoquinones lie practically in one plane.

Thermally resistant air-stable organic triradicals with a quartet ground state and a large energy gap between spin states are still unique compounds. In this work, we succeeded to design and prepare the first highly stable triradical, consisting of oxoverdazyl and nitronyl nitroxide radical fragments, with a quartet ground state. The triradical and its diradical precursor were synthesized via a palladium-catalyzed cross-coupling reaction of diiodoverdazyl with nitronyl nitroxide-2-ide gold(I) complex. Both paramagnetic compounds were fully characterized by single-crystal X-ray diffraction analysis, superconducting quantum interference device magnetometry, EPR spectroscopy in various matrices, and cyclic voltammetry. In the diradical, the verdazyl and nitronyl nitroxide centers demonstrated full reversibility of redox process, while for the triradical, the electrochemical reduction and oxidation proceed at practically the same redox potentials, but become quasi-reversible. A series of high-level CASSCF/NEVPT2 calculations was performed to predict inter- and intramolecular exchange interactions in crystals of di- and triradicals and to establish their magnetic motifs. Based on the predicted magnetic motifs, the temperature dependences of the magnetic susceptibility were analyzed, and the singlet-triplet (135 ± 10 cm-1) and doublet-quartet (17 ± 2 and 152 ± 19 cm-1) splitting was found to be moderate. Unique high stability of synthesized verdazyl-nitronylnitroxide triradical opens new perspectives for further functionalization and design of high-spin systems with four or more spins.

A 4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl lithium derivative was found to react with 2-methoxypentafluoro-1,4-naphthoquinone to form a product of addition at the carbonyl function: radical 2-(3,5,6,7,8-pentafluoro-1-hydroxy-2-methoxy-4-oxo-1,4-dihydronaphthalen-1-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl. The yield of the addition product increased with temperature and reached 84% at 0 °C. The reaction of the lithium derivative with hexafluoro-1,4-naphthoquinone gave rise to a product of addition at both carbonyl groups, namely, nitronyl nitroxide diradical 2,3,5,6,7,8-hexafluoro-1,4-bis(4,4,5,5-tetramethyl-3-oxide-1-oxyl-4,5-dihydro-1H-imidazole-2-yl)-1,4-dihydronaphthalene-1,4-diol in a 16% yield. The structures of both mono- and diradical were solved by X-ray diffraction analysis, which revealed formation of an intramolecular H-bond between the OH group and nitroxide oxygen. According to electron paramagnetic resonance (EPR) spectroscopy, the obtained mono- and dinitroxide are prone to spontaneous deoxygenation in a toluene solution to give corresponding iminonitroxides. In water, they are much more stable.

Reactions of hexafluoro-1,4-naphthoquinone with phosphorus-centered bis-phenylphosphanes with structure Ph2P(CH2)nPPh2 (where n = 1–5) and Et2P(CH2)2PEt2 in various solvents (anhydrous C6H6, aq. C6H6, aq. dioxane, aq. DMSO, or MeOH) were investigated. It was shown that the use of aqueous dioxane and DMSO leads to target products of phosphanodefluorination (i.e., phosphorus-containing betaines and bis-betaines) with high yields. We found that the betaines upon purification by thin-layer chromatography underwent various transformations such as a ring contraction (thus yielding novel polyfluorinated indenones) or addition of an acetone molecule at the C O bond of the fluorinated 1,4-naphthoquinone. According to X-ray diffraction analysis, there were intermolecular F⋯π interactions in the crystal packing of all the obtained betaines. The interactions are characterized by short distances F⋯Cg from 3.151(5) to 3.831(2) A (where Cg is a centroid of π-system).

WOS:000430904400002; Recently, we reported on the activation of the C-ON bond homolysis in alkoxyamines R1R2NOR3 using the coordination of the alkyl fragment R-3 with metal cations Cu(II) and Zn(II). Here, we report the selective coordination of the diethylphosphoryl group carried by the nitroxyl fragment by the oxophilic metal cation Tb(III). Coordination on the nitroxyl fragment afford a slight 2-fold decrease in the C-ON bond homolysis rate constant kd. (C) 2018 Elsevier B.V. All rights reserved.

WOS:000481879400050; International audience; Because the C-ON bond homolysis rate constant k(d) is an essential parameter of alkoxyamine reactivity, it is especially important to tune k(d) without a major alteration of the structure of the molecule. Recently, several approaches have become known, e.g., protonation of functional groups and formation of metal complexes. In this paper, coordination reactions of [Zn(hfac)(2)(H2O)(2)] with a series of new SG1-based alkoxyamines affording complexes with different structures are presented. The k(d) values of the complexed forms of the alkoxyamines were compared to those of free and protonated ones to reveal the contribution of the electron-withdrawing property and structure stabilization. Together with previously published data, this work provides clues to the design of alkoxyamines that can be effectively activated upon coordination with metal ions. Furthermore, our results provide insight into the mechanism underlying the influence of complexation on the reactivity of alkoxyamines. This led us to describe different types of coordination: intramolecular in nitroxyl fragment, intramolecular in alkyl fragment, intramolecular between alkyl and nitroxyl fragment, and intermolecular one. All of them exhibit different trends which are dramatically altered by changes in conformation.

Fluorinated derivatives of 1,4-naphthoquinones are highly potent inhibitors of Cdc25A and Cdc25B phosphatases; they suppress the growth of tumor cells. Four derivatives of phosphonium betaines derived from hexafluoro-1,4-naphthoquinone: (triphenyl[5,6,7,8-tetrafluoro-1-oxido-4-oxo-3-(phenylimino)-3,4-dihydronaphthalen-2-yl]phosphonium) (4), ((3,5-difluorophenyl)(methyl)phenyl(5,6,7,8-tetrafluoro-3-oxido-1,4-dioxo-1,4-dihydronaphthalen-2-yl)phosphonium) (5), ((2,5-difluorophenyl)(methyl)phenyl(5,6,7,8-tetrafluoro-3-oxido-1,4-dioxo-1,4-dihydronaphthalen-2-yl)phosphonium) (6) and ((3,5-difluorophenyl)diphenyl(5,6,7,8-tetrafluoro-3-oxido-1,4-dioxo-1,4-dihydronaphthalen-2-yl)phosphonium) (7) were synthesized for the first time. Their cytotoxicity toward human mammary adenocarcinoma, human myeloma, hamster and murine and fibroblasts as well as their antioxidant and mutagenic effects on a Salmonella tester strain were analyzed. All four substances showed comparable IC50 values in terms of suppression of tumor cell growth, which were from two- to ninefold lower comparing with those of fibroblasts. To identify the features of spatial orientation and noncovalent interactions of the new phosphonium betaines in the binding site of Cdc25B, a molecular docking analysis was carried out. It showed that the interactions of the analyzed compounds with a Cdc25B model binding site are characterized by the presence of a large number of acceptors (fluorine and oxygen atoms, forming halogen and hydrogen bonds) and by participation of pi-systems and phosphorus in specific electrostatic interactions that may result in inhibition of enzymes of the Cdc25 family. In addition, compounds 5 and 6 (especially the latter) were found to be effective antioxidants protecting bacterial cells from H2O2-induced and spontaneous and mutagenesis at significantly lower concentrations (IC50 = 0.09 to 1.8 μM) than those of derivatives 4 and 7 (86–92 μM). Taking into account these data (together with the good cytotoxic effect on cancer cells comparing with normal mammalian cells) we can propose compounds 5 and 6 as possible useful inhibitors of tumor cell growth and antioxidants.

Aim: Synthesis and analysis of antioxidant and antitumor properties of fluorinated phosphorus- containing derivatives of tetrafluoro-1,4-benzoquinone and hexafluoro-1,4-naphthoquinone. Methodology: All compounds were synthesized by amino- and phosphanodefluorination with corresponding amines and phosphanes. The cytotoxicity of these fluorinated benzoquinones and Original Research Article

International audience; The metal complexation reactions of bis(hexafluoroacetylacetonato)copper(II)(Cu(hfac)(2)) with alkoxyamines (diethyl(2,2-dimethyl-1-(tert-butyl-(1-(pyridine-4-yl)ethoxy)amino)propyl)phosphonate and diethyl (2,2-dimethyl-1-(tert-butyl-(1-(pyridine-2-yl)ethoxy)amino)propyl)phosphonate) were studied. According to X-ray analysis, the molecular and crystal structures of 1:1 complexes depend on the configuration of the free alkoxyamines, that is dimeric (RSSR) and chain-polymeric (RR/SS) structures for para-pyridyl-substituted alkoxyamines, and cyclic unimeric (RS/SR) structure for ortho-pyridyl derivative. The complex (2:1 ratio Cu(hfac)(2)/alkoxyamine) for ortho-pyridyl-substituted alkoxyamine is not resolved. Upon warming, ortho complexes decomposed into free alkoxyamines and only a weak activation was observed. Upon warming, para complexes decomposed into their corresponding unimers, and then, a 21-fold increase in the rate constant of the C-ON bond homolysis was observed compared to the corresponding free alkoxyamines. Tuning of the homolysis rate constant of the C-ON bond via addition of pyridine is also reported.

WOS:000432826800003; Preparation of materials by nitroxide-mediated polymerization (NMP) is well known nowadays. To increase the possible usefulness of NMP for the production of hybrid materials or polymer-decorated complexes, coordination-initiated NMP (CI-NMP) was developed and investigated here. CI-NMP was exemplified using the instantaneous and spontaneous reaction of alkoxyamines carrying a pyridyl moiety on the alkyl group and the Zn(hfac)(2) (hfac: hexafluoroacetylacetonate) complex as a metal centre. NMP of styrene and n-butyl acrylate was carried out with either previously or in situ-prepared complexes. Both approaches afforded NMP of the same quality. The positive influence of metal centre coordination is highlighted by efficient NMP at 90 degrees C.

International audience; A series of Zn(hfac)(2) alkoxyamines (diethyl(2,2-dimethyl-1-(tert-butyl-(1-pyridylethoxy)amino)propyl)phosphonate) coordinated at ortho, meta and para positions of their pyridyl moiety were prepared and their homolysis rate constants k(d) measured. Up to a 30-fold increase in k(d) was observed for the meta-(Zn-RR/SS) and para-(Zn-RR/SS) regioisomers. Moreover, the activation is also controlled by the amount of pyridine, used as a ligand competitor. XRD, H-1 and P-31 NMR spectra show very different structures for each complexes in solid state and in solution depending on the diastereosiomers and on the regioisomers.

International audience; Recently, new applications of trityl-nitroxide biradicals were proposed. In the present study, attachment of a trityl radical to alkoxyamines was performed for the first time. The rate constants k(d) of C-ON bond homolysis in these alkoxyamines were measured and found to be similar to those for alkoxyamines without a trityl moiety. The electron paramagnetic resonance (EPR) spectra of the products of alkoxyamine homolysis (trityl-TEMPO and trityl-SG1 biradicals) were recorded, and the corresponding exchange interactions were estimated. The decomposition of trityl-alkoxyamines showed more than an 80% yield of biradicals, meaning that the C-ON bond homolysis is the main reaction. The suitability of these labelled initiators/controllers for polymerisation was exemplified by means of a successful nitroxide-mediated polymerisation (NMP) of styrene. Thus, this is the first report of a spin-labelled alkoxyamine suitable for NMP.