Li<sup>+</sup>-Catalyzed Radical Polymerization of Simple Terminal Alkenes

Vyakaranam, Kamesh; Barbour, Josiah B.; Michl, Josef

doi:10.1021/ja060087+

Cited by 71 publications

(86 citation statements)

References 28 publications

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“…However, for a ring-closure-type radical clock, we [19] were able to show that complexation of the double bond of the intermediate hex-1-en-6-yl radical [20] to a lithium cation decreases the calculated activation barrier for the ring-closing rearrangement significantly. This effect is supported indirectly by recent work of Michl and co-workers, [21,22] who showed that "naked" lithium cations have a catalyzing effect on the radical polymerization of terminal olefins, in accord with a proposal made 20 years ago on the basis of ab initio calculations [23] and a recent more-detailed study at higher theoretical levels. [24] However, all these observations pertain to radicals that contain a double bond, which can complex the lithium cation moderately well.…”

Section: Introductionsupporting

confidence: 56%

The Effect of a Complexed Lithium Cation on a Norcarane‐Based Radical Clock

Jäger

Hennemann

Clark

2009

Chemistry A European J

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Density-functional theory (DFT) and ab initio calculations have been used to investigate the effect of a complexed lithium cation on the radical-clock rearrangement of the 2-norcaranyl radical to the 3-cyclohexenylmethyl radical. As found earlier for ring-closing radical clocks, complexation with a metal ion leads to a significant lowering of the barrier to rearrangement. DFT calculations on a model for the norcaranyl clock in cytochrome P450 confirm the two-state reactivity proposal of Shaik et al. and indicate that the porphyrin exerts little or no electrostatic effect on the rearrangement barrier.

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Section: Introductionsupporting

confidence: 56%

The Effect of a Complexed Lithium Cation on a Norcarane‐Based Radical Clock

Jäger

Hennemann

Clark

2009

Chemistry A European J

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“…LiCl induced heterotactic specificity in CF 3 CH 2 OH, which was the same as LiNTf 2 . 59 The addition of an equimolar amount of NaNTf 2 or KNTf 2 also enhanced the polymer yields and molecular weights when the DMAAm polymerization reaction was conducted in polar solvents, except for KNTf 2 in CF 3 CH 2 OH (Table 4, runs [30][31][32][33][34][35]. The r diad content reached up to 65% in THF, which is comparable to the highest r diad content of 69% reported to date for radically prepared poly (DMAAm)s. 58 On the other hand, LiOTf exhibited a different effect to that of LiNTf 2 and LiCl, in that it gave syndiotactic-Scheme 2 Relationship between the stoichiometry of the DMAAm-Li + complex and the stereospecificity of the DMAAm polymerization.…”

Section: Relationship Between Complex Structure and Stereospecificitymentioning

confidence: 55%

Dual role for alkali metal cations in enhancing the low-temperature radical polymerization of N,N-dimethylacrylamide

et al. 2015

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The radical polymerization of N,N-dimethylacrylamide (DMAAm) has been investigated in the presence of several alkali metal salts, including lithium bis(trifluoromethanesulfonyl)imide (LiNTf 2 ). The addition of an alkali metal salt led to a significant increase in the yield and molecular weight of the resulting polymer.NMR analysis of mixtures of DMAAm and LiNTf 2 suggested that DMAAm was being activated by the coordination of Li + to its CvO group. Electron spin resonance analysis of the DMAAm polymerization in the presence of LiNTf 2 suggested that the propagating radical was being stabilized by Li + through a single-electron lithium bond, because a signal for the propagating radical of the acrylamide derivatives was observed for the first time in solution when LiNTf 2 was added. Based on these results, we have proposed a mechanism for this polymerization, where the propagation steps occur between a lithium ionstabilized propagating radical and a lithium ion-activated incoming monomer. Furthermore, polymers with a wide range of stereoregularities, such as isotactic, syndiotactic and heterotactic systems, were successfully prepared using this method by carefully selecting the appropriate combination of solvent and alkali metal salt. † Electronic supplementary information (ESI) available: Dependence of polymer yield on the added amount of LiNTf 2 in toluene, additional 1 H NMR spectra of the main-chain methylene groups of the poly(DMAAm)s prepared in this study and changes in the chemical shifts of DMAAm in the presence of MNTf 2 . See View Article Online a [Monomer] 0 = 1.0 mol L −1 , [MAIB] 0 = 1.0 × 10 −2 mol L −1 , [alkali metal salts] 0 = 1.0 mol L −1 . b Determined from 1 H NMR signals. c Determined by SEC (PMMA standards). d Alkali metal salt was not completely dissolved. e Polymer precipitated during polymerization reaction. Polymer Chemistry PaperThis journal is

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“…After a day on the benchtop, these microcrystalline powders spontaneously turn into an oligomeric gummy material whose NMR no longer shows any vinylic protons. 15 This transformation does not occur in the absence of air, and it was ultimately proposed that oxygen acts as a radical initiator, 16 likely by oxidizing the carborate anion to a radical, which in turn initiates polymerization. Our group has since used oxygen to initiate other alkene radical polymerizations in the presence of LiCB 11 (CH 3 ) 12 under ambient conditions.…”

Section: Methodsmentioning

confidence: 99%

Highly Branched Polypropylene via Li⁺-Catalyzed Radical Polymerization

et al. 2011

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b S Supporting Information W hile radical polymerization techniques are well suited for polar monomers, they are not used to polymerize simple R-olefins as the allylic hydrogens on the latter are subject to chain transfer in the presence of a reactive propagating radical. 1 Thus, with the exception of ethylene produced commercially at very high pressures and temperatures (and a few reports of propylene under similar intense conditions 2,3 ), only short oligomers of simple alkenes such as propylene or 1-hexene can be obtained using conventional radical polymerization techniques. Against this backdrop, our group recently reported that a variety of simple alkenes could, in fact, be polymerized under radical conditions at ambient temperatures and pressures in the presence of a lithium cation in the form of LiCB 11 (CH 3 ) 12 . 4 By all indications, including the use of radical and ionic traps, the polymerization proceeds as a radical process. We believe that Li þ coordination to the alkene in weakly ligating organic media alters the relative rates of propagation and degradative chain transfer in favor of propagation (Scheme 1).Following these initial reports, we began investigating this system more fully with isobutylene, whose six allylic hydrogens render it a most unlikely candidate for radical polymerization. 5 This system proved quite unique, as it appears that both a radical process and a cationic one can be induced simultaneously. Under nonoxidative conditions, the radical process produced a polyisobutylene (b-PIB) with a highly branched architecture, unlike anything previously reported or prepared commercially. Under oxidative conditions, the radical process still occurred and produced b-PIB, while a concurrent cationic one generated perfectly linear l-PIB that differed from ordinary PIB only in that a carborate anion was covalently attached at the chain end. 6 Under these conditions, LiCB 11 (CH 3 ) 12 acted not only as a catalyst but also as a reagent and could not be recovered from the reaction mixture quantitatively or at all. A concurrent study of LiCB 11 (CH 3 ) 12 -catalyzed radical polymerization of 1-hexene and 1-octene has so far only revealed the formation of low molecular weight oligomers. 7 The contrast to the polymerization of propene described below is striking, and other reaction conditions are still being examined.Here, we report on our investigation of the nature and architecture of polypropylene (PP) that is generated under nonoxidizing conditions in the weakly ligating solvent 1,2-dichloroethane (DCE), using azo-tert-butane (ATB) initiator. Figure 1 illustrates the 13 C NMR spectrum of a sample of b-PP generated at moderate pressures (15 atm) and temperatures (80°C) in DCE solvent with ATB initiation under LiCB 11 (CH 3 ) 12 catalysis (for precise experimental conditions see Supporting Information). Polymer yield in this reaction was around 40%. The b-PP formed is very highly branched, as can be seen by the plethora of resonances observed in the spectrum between 10 and 45 ppm, which is unli...

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Li⁺-Catalyzed Radical Polymerization of Simple Terminal Alkenes

Cited by 71 publications

References 28 publications

The Effect of a Complexed Lithium Cation on a Norcarane‐Based Radical Clock

The Effect of a Complexed Lithium Cation on a Norcarane‐Based Radical Clock

Dual role for alkali metal cations in enhancing the low-temperature radical polymerization of N,N-dimethylacrylamide

Highly Branched Polypropylene via Li⁺-Catalyzed Radical Polymerization

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Li+-Catalyzed Radical Polymerization of Simple Terminal Alkenes

Cited by 71 publications

References 28 publications

The Effect of a Complexed Lithium Cation on a Norcarane‐Based Radical Clock

The Effect of a Complexed Lithium Cation on a Norcarane‐Based Radical Clock

Dual role for alkali metal cations in enhancing the low-temperature radical polymerization of N,N-dimethylacrylamide

Highly Branched Polypropylene via Li+-Catalyzed Radical Polymerization

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Product

Resources

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Li⁺-Catalyzed Radical Polymerization of Simple Terminal Alkenes

Highly Branched Polypropylene via Li⁺-Catalyzed Radical Polymerization