Coordination-Initiated Nitroxide-Mediated Polymerization (CI-NMP)

WOS:000432826800003Preparation 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

AMOS-E

Abstract A homopolymer of N,N-bis(vinyloxyethyl)thiuramdisulphide was synthesized via cationic polymerization and investigated as a sorbent of the ions of mercury and precious metals. The effect of the nature and concentration of acid, phase contact time on the extraction of metals was revealed; sorption capacities of the polymer and metal partition coefficients were estimated. It was shown that the sorbent exhibits high sorption activity to metal ions in the cationic form: with respect to mercury (Hg 2+ ) from 1 M HNO 3 solution 1100 mg/g, 1M H 2 SO 4 990 mg/g, 1 M HCl 280 mg/g; with respect to silver (Ag + ) from 1 M HNO 3 850 mg/g, from 1 M H 2 SO 4 900 mg/g. A mechanism of the interaction of active groups of the sorbent with metal ions was proposed on the basis of IR spectroscopic data. The homopolymer of N,Nbis(vinyloxyethyl)thiuramdisulphide sorbs mercury and silver ions selectively from a mixture of copper, nickel, iron and zinc salts. The possibility to use the sorbent for concentrating precious metals and for an alytical purposes was demonstrated. A method of sorbent regeneration was developed

Zinc(II) Hexafluoroacetylacetonate Complexes of Alkoxyamines: NMR and Kinetic Investigations. First Step for a New Way to Prepare Hybrid Materials

International audienceA 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

C-ON bond homolysis of alkoxyamines triggered by paramagnetic copper(II) salts

International audienceThe 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

The effect of the oxophilic Tb(III) cation on C-ON bond homolysis in alkoxyamines

WOS:000430904400002Recently, 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

How intramolecular coordination bonding (ICB) controls the homolysis of the C-ON bond in alkoxyamines

WOS:000481879400050Because 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

Ferromagnetic Chain Based on Verdazyl-Nitroxide Diradical

Verdazyl-nitroxide diradicals were synthesized using the palladium-catalyzed cross-coupling reaction of the corresponding iodoverdazyls with a nitronyl nitroxide-2-ide gold(I) complex with high yields (up to 82%). The synthesized diradicals were found to be highly thermally stable and have a singlet (DEST » -64 cm–1) or triplet ground state (DEST ³ 25 and 100 cm–1), depending on which canonical hydrocarbon diradical type they belong to. Upon crystallization, triplet diradicals form unique one-dimensional (1D) spin S = 1 chains of organic diradicals with intrachain ferromagnetic coupling of J′/kB from 3 to 6 K.</p

Platform for High-Spin Molecules: A Verdazyl-Nitronyl Nitroxide Triradical with Quartet Ground State

Quartet verdazyl-nitronylnitroxide triradical was synthesized via palladium-catalyzed cross-coupling reaction of the corresponding diiodoverdazyls with a nitronyl nitroxide-2-ide gold(I) complex. The triradical is air-stable and possess good thermal stability with decomposition onset at ∼160 °C in an inert atmosphere. X-ray diffraction analysis of single crystals confirmed the presence of verdazyl and nitroxide radical centers. Magnetic properties were characterized by a SQUID magnetometry of polycrystalline powders and by EPR spectroscopy in different matrices. Collected data analyzed using of the high-level quantum chemical calculations confirmed that the triradical has high-spin ground states.<br /