Single Component Iron Catalysts for Atom Transfer and Organometallic Mediated Radical Polymerizations: Mechanistic Studies and Reaction Scope

Allan, Laura E. N.; MacDonald, Jarret P.; Nichol, Gary S.; Shaver, Michael P.

doi:10.1021/ma402381x

Cited by 56 publications

(69 citation statements)

References 94 publications

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“…The size of k deact makes amine−bis(phenolate)iron an attractive catalyst system for well-controlled RDRPs. 12,13 ■ CONCLUSIONS Both the paramagnetic metal complexes and, with high time resolution, the propagating radicals may be detected via EPR. The SP−PLP−EPR technique has already been used to study Cu II -mediated deactivation rate as well as Cu I -and Fe IImediated organometallic reactions.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…2-Ethylhexyl methacrylate (EHMA, Aldrich, 98%) was treated with inhibitor remover (Aldrich) and degassed by several freeze−pump−thaw cycles. The amine−bis-(phenolate)iron(III) halide complex, Cl,Cl,NMe2 [O 2 NN′]Fe III Cl (see Figure 1A), was prepared following literature procedures 13 EPR Measurements. EPR measurements were performed on a Bruker EPR CW/transient spectrometer Elexsys-II 500T.…”

Section: ■ Introductionmentioning

confidence: 99%

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SP–PLP–EPR Measurement of Iron-Mediated ATRP Deactivation Rate

Schroeder

Buback

2015

Macromolecules

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The rate of ATRP deactivation was measured for the amine−bis(phenolate)iron-mediated polymerization of 2-ethylhexyl methacrylate (EHMA). EHMA radical concentration is monitored by highly time-resolved EPR spectroscopy after pulsed-laser-induced radical production. In addition, the concentration of the iron(III) complex was measured via EPR. The SP−PLP−EPR method allows for the analysis of ATRP deactivation rate without interference by potential organometallic reactions. Toward higher temperature, the ratio of deactivation to propagation rate increases, which is beneficial for ATRP control. ■ INTRODUCTIONReversible-deactivation radical polymerization (RDRP) has been extensively used for synthesizing polymeric materials with precisely tailored topology, architecture, chain length, functionality, and narrow molar-mass distribution. 1−3 Fe catalysts are attractive for RDRP due to the low toxicity and broad availability of iron. 4,5 Moreover, Fe catalysts may be used for two RDRP techniques, i.e., for atom-transfer radical polymerization (ATRP) 6 and for organometallic-mediated radical polymerization (OMRP). 7−11 Both methods are based on a metal-mediated activation−deactivation equilibrium of propagating radicals involving the Fe catalyst in different oxidation states and may even operate simultaneously. 7,10,12−17 Because of the kinetic complexity, the precise knowledge of the mechanism and of the individual rate coefficients is necessary for improving Fe-mediated RDRP. EPR spectroscopy is particularly useful for investigations into the kinetics of radical polymerization, as the relevant radical species may be quantitatively monitored online. 18−20 Highly time-resolved EPR spectroscopy in conjunction with laser pulsing has emerged as the state-of-the-art method, since even very fast reaction steps such as termination or deactivation may be accurately monitored. 18,19 In single-pulse−pulsed laser polymerization (SP−PLP), a high concentration of primary radicals is almost instantaneously produced by the laser-induced decomposition of a photoinitiator. The chain length, i, of radicals increases according to the relation i = k p × c M × t + 1, where k p is the propagation rate coefficient, c M the monomer concentration, and t the time after applying the laser pulse. The term +1 represents the initiator fragment which starts chain growth. SP−PLP is similar to RDRP in that i progressively increases with time and molar mass distribution of the propagating radicals is narrow. Time-resolved monitoring may be carried out for different types of radical species which may evolve after laser-induced production of primary radical fragments. For example, in acrylate polymerizations the concentration of both secondary propagating radicals (SPRs) and midchain radicals, formed from SPRs via backbiting, 21−24 was determined by EPR analysis at separate magnetic field positions. 25,26 Metal complexes with unpaired electrons such as Cu II or high-spin Fe III are 27 With both the propagating radicals and the Fe III -catalyst species bein...

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Section: ■ Results and Discussionmentioning

confidence: 99%

Section: ■ Introductionmentioning

confidence: 99%

SP–PLP–EPR Measurement of Iron-Mediated ATRP Deactivation Rate

Schroeder

Buback

2015

Macromolecules

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“…14 vs. 15 and 17 vs. 18), which manifests in higher % conversions, while the bromide-containing complexes generally provided better control over the polymerisation (lower Ð). Kinetic investigations of the CRP reaction mediated by one of the most efficient complexes in this family (14) gave a pseudo first-order rate constant of 1.02 h -1 (44), which is amongst the highest measured for iron catalysts in styrene polymerization (32,45).…”

Section: Copyright (2012) John Wiley and Sonsmentioning

confidence: 88%

“…In order to directly probe the OMRP mechanism (in the absence of R-ATRP), the polymerization of styrene using an in situ generated Fe II complex and conventional radical initiator (AIBN) was attempted (44). The Fe II complex was generated in situ since previous attempts at synthesising a stable and isolable Fe II -ABP complex had proved fraught with difficulty.…”

confidence: 99%

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The Interplay of ATRP, OMRP and CCT in Iron-Mediated Controlled Radical Polymerization

Lake

Shaver

2015

ACS Symposium Series

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Ligand‐Promoted Iron(III)‐Catalyzed Hydrofluorination of Alkenes

Xie

Sun

et al. 2019

Angewandte Chemie

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An iron-catalyzedhydrofluorination of unactivated alkenes has been developed. The use of am ultidentate ligand and the fluorination reagent N-fluorobenzenesulfonimide (NFSI) proved to be critical for this reaction, whicha fforded various fluorinated compounds in up to 94 %y ield.Scheme 2. Optimization of the reaction conditions. Reactionsw ere carried out with 1a (0.2 mmol) in EtOH (2.0 mL for conditions A; 1.0 mL for conditions B)u nder N 2 .Y ields are for the isolated product. Ln-FeCl 3 : Ln (5 mol %), FeCl 3 (5 mol %). Angewandte ChemieZuschriften 7172 www.angewandte.de Scheme 4. Scope of the reaction of di-and trisubstituted alkenes. Reactionsw ere carried out with 1 (0.2 mmol) in EtOH (1.0 mL) or EtOH/CH 2 Cl 2 (1:2, 1.0 mL) at 75 8 8Cunder N 2 for 3h.Yields are for the isolated product.[a] Ratio of trans/cis isomers (trans isomer is major).[b] Ratio of regioisomers.[c] The trisubstituted alkene 3-methylbut-2en-1-yl 2-naphthoate was used. Piv = pivaloyl.Scheme 5. Competition experiments. 2-Np = 2-naphthyl.

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Single Component Iron Catalysts for Atom Transfer and Organometallic Mediated Radical Polymerizations: Mechanistic Studies and Reaction Scope

Cited by 56 publications

References 94 publications

SP–PLP–EPR Measurement of Iron-Mediated ATRP Deactivation Rate

SP–PLP–EPR Measurement of Iron-Mediated ATRP Deactivation Rate

The Interplay of ATRP, OMRP and CCT in Iron-Mediated Controlled Radical Polymerization

Ligand‐Promoted Iron(III)‐Catalyzed Hydrofluorination of Alkenes

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