Switched external magnetic field CIDNP studies of coupling reaction of carbon-centered radicals with TEMPO

Lebedeva, N. V.; Zubenko, Dmitry; Bagryanskaya, Elena G.; Sagdeev, R. Z.; Ananchenko, Gennady S.; Marque, Sylvain R. A.; Bertin, Denis; Tordo, Paul

doi:10.1039/b401093k

Cited by 31 publications

(25 citation statements)

References 38 publications

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“…k c given in Table 1 unless otherwise mentioned. i ) The influence of the ester-group size on k c was assumed to be insignificant, see [25]. j ) Estimated from E a A C H T U N G T R E N N U N G (1a) À 19.1 kJ/mol (see [28]).…”

Section: Experimental Partmentioning

confidence: 99%

2,5‐Dihydro‐1H‐imidazole‐Based Nitroxides as Prospective Mediators in Living Radical Polymerization

Zubenko

Kirilyuk

Roshchupkina

et al. 2006

Helvetica Chimica Acta

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Dedicated to the memory of Professor Hanns FischerA number of spectroscopic methods were applied to obtain kinetic parameters of reactions modelling the 2,5-dihydro-1H-imidazole 1-oxide mediated living polymerization of acrylates. The homolysis rate constants of alkoxyamines based on five nitroxides were measured by EPR spectroscopy at different temperatures. The recombination rate constants k c between the corresponding alkyl radicals and the nitroxides were measured by means of laser flash photolysis. The time-resolved chemically induced dynamic nuclear polarization (TR-CIDNP) experiments revealed the negligible contribution of disproportionation in the recombination reaction. In addition, the thermodecomposition of alkoxyamines in the NMR probe showed the absence of intramolecular elimination of hydroxylamines from the corresponding alkoxyamines. Analysis of the kinetic parameters showed that the 2,5-dihydro-1H-imidazole 1-oxide type radicals are promising mediators for the living polymerization of acrylates and methacrylates.Introduction. -Nitroxide-mediated polymerization [1] [2] (NMP) is a fine synthetic technique, which allows for the design of new types of homo-and copolymers with welldefined architectures and narrow molecular-mass distributions [3]. The principal mechanism of NMP (Scheme 1) involves the reversible dissociation of a dormant nitroxide end-capped polymer chain with rate constant k d , the propagation of C-centered radicals with rate constant k p , the cross-coupling reaction between the nitroxide and the growing polymer chain with rate constant k c , and simultaneous irreversible self-termination reactions of the C-centered radicals with rate constant k t .

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Section: Experimental Partmentioning

confidence: 99%

2,5‐Dihydro‐1H‐imidazole‐Based Nitroxides as Prospective Mediators in Living Radical Polymerization

Zubenko

Kirilyuk

Roshchupkina

et al. 2006

Helvetica Chimica Acta

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“…Coupling of R  with TEMPO (Eq. 5) was considered to be an irreversible reaction with a rate constant of 10 9 M -1 s -1[37,53,54]. ATRP equilibrium constants, K ATRP , for the 7×10 M -1 s -1 ).…”

mentioning

confidence: 99%

Electrochemical approaches to the determination of rate constants for the activation step in atom transfer radical polymerization

Fantin

Isse

Bortolamei

et al. 2016

Electrochimica Acta

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Direct determination of ATRP activation rate constant, kact, is typically limited to slow or moderately fast reactions: kact< 102 mol1dm3 s1 were determined by classical techniques, such as chromatography, spectrophotometry, NMR, etc. Therefore, these techniques are inadequate to study the fastest, and most useful, ATRP systems, such as the most frequently used Cu complexes with tris[2-(dimethylamino)ethyl] amine (Me6TREN), tris(2-pyridylmethyl)amine (TPMA) and substituted TPMA. In this study, electrochemical methods have been used to investigate the kinetics of activation of a series of typical ATRP initiators (RX) by [CuIL]+ (L = Me6TREN, TPMA or N,N,N0,N00,N0 0-pentamethyldiethylenetriamine, (PMDETA) in MeCN. Both high (>104 mol1dm3 s1) and low kact values have been measured. Analysis of the collected data showed that kact depends on E of the catalyst, molecular structure of RX, and nature of the halogen atom. Although usually values of kact increase with decreasing standard reduction potential of [CuIIL]2+, there is no well-defined correlation between the two parameters. Instead, kact gives good and\ud useful linear correlations with the standard reduction potential of [XCuIIL]+, and with KATRP or Gibbs free energy of C-X bond dissociation

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“…Nevertheless we failed to detect both the IH and ~3C CIDNP under the photolysis of DBK in SDS micelles at even such small bulk concentration of TEMPO as 1.5 mM. It is worthwhile to note that in benzene solutions the ~H CIDNP acquired from the photolysis products could be detected so easily that SEMF CIDNP allowed for measuring the recombination rate constants between TEMPO and benzyl radicals in low magnetic fields [41].…”

Section: Dbkmentioning

confidence: 99%

“…5 shows that addition of TEMPO not only decreases the CIDNP intensity of the products of recombination of the geminate radical pair, but the new nuclear polarized signal due to polarization transfer also appears in the NMR spectrum. This signal can be assigned to CH 3 protons of the alkoxyamine [41] produced in reaction of TEMPO and di-methyt isobutyrate-2-yl radical.…”

Section: 2'44'-tetramethyldimethyl Acetone Dicarboxylatementioning

confidence: 99%

Influence of nitroxides on CIDNP of micellised radical pairs and short-lived biradicals

Shakirov¹,

Lebedeva²,

Gorelik³

et al. 2006

Appl. Magn. Reson.

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The effects of stable nitroxide radicals on stimulated nuclear polarization (SNP) and chemically induced dynamic nuclear polarization (CIDNP) in short-lived consecutive biradicals and radical pairs in homogeneous solutions as well as spin-correlated radical pairs in micelles were studied in high and low magnetic fields. It is shown that experimentally observed effects of nitroxide additions on CIDNP and SNP can be well simulated taking into account only the increase in the rates of relaxation in the paramagnetic species constituting radical pairs or biradicals. Effects of coherent spin evolution in three-spin systems under study seem to be of negligible importante.

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Switched external magnetic field CIDNP studies of coupling reaction of carbon-centered radicals with TEMPO

Cited by 31 publications

References 38 publications

2,5‐Dihydro‐1H‐imidazole‐Based Nitroxides as Prospective Mediators in Living Radical Polymerization

2,5‐Dihydro‐1H‐imidazole‐Based Nitroxides as Prospective Mediators in Living Radical Polymerization

Electrochemical approaches to the determination of rate constants for the activation step in atom transfer radical polymerization

Influence of nitroxides on CIDNP of micellised radical pairs and short-lived biradicals

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