N‐Heterocyclic carbenes for metal‐free polymerization catalysis: an update

Naumann, Stefan; Dove, Andrew P.

doi:10.1002/pi.5034

Cited by 58 publications

(55 citation statements)

References 89 publications

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“…presented in 1991 the first successful isolation of a stable N‐heterocyclic carbene (NHC) . Since this achievement, NHCs have been at the forefront of organometallic chemistry, catalysis, and more recently polymerization . To date, the most frequently encountered NHCs are 1,3‐bis(mesityl)imidazol‐2‐ylidene (IMes, 1 ) and its saturated congener 1,3‐bis(mesityl)imidazolidin‐2‐ylidene (SIMes, 2 ) (Figure ).…”

Section: Introductionmentioning

confidence: 99%

“…In polymerization, they can replace organometallic compounds with advantages of reducing cost and toxicity. The range of NHC‐mediated polymerizations already covers ring‐opening polymerization (lactone, lactam, epoxide) as well as step‐growth polymerization for the synthesis of polybenzoin or polyurethane …”

Section: Introductionmentioning

confidence: 99%

“…[9] In addition, their strong nucleophilicity and Brønsted basicityh ave contributed to their use as organocatalysts. In polymerization, they can replaceo rganometallic compounds with advantages of reducing cost and toxicity.T he rangeo fN HC-mediated polymerizations [5,10,11] already covers ring-opening polymerization( lactone, [12] lactam, [13] epoxide [14] ) as well as step-growth polymerization for the synthesis of polybenzoin [15] or polyurethane. [16] Despite the wealth of research conducted to date,t he practical use of NHCs presents an umbero fc hallenges:N HCs are highlys ensitivet om oisture, and must be handled under ad ry atmosphere.M oreover,t hey reactw ith acidsd ue to their high pK a ,a nd are also prone to dimerization.…”

Section: Introductionmentioning

confidence: 99%

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Mixture of Azolium Tetraphenylborate with Isopropylthioxanthone: A New Class of N‐Heterocyclic Carbene (NHC) Photogenerator for Polyurethane, Polyester, and ROMP Polymers Synthesis

Trinh

Malval

Morlet‐Savary

et al. 2019

Chemistry A European J

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In the search of smarter routes to control the conditions of N‐heterocyclic carbene (NHCs) formation, a two‐component air‐stable NHC photogenerating system is reported. It relies on the irradiation at 365 nm of a mixture of 2‐isopropylthioxanthone (ITX) with 1,3‐bis(mesityl)imidazoli(ni)um tetraphenylborate. The photoinduced liberation of NHC is evidenced by reaction with a mesitoyl radical to form an NHC‐radical adduct detectable by electron spin resonance spectroscopy. The NHC yield can be determined by 1H NMR spectroscopy through the formation of a soluble and stable NHC–carbodiimide adduct. To deprotonate the azolium salt and liberate the NHC, a mechanism is proposed in which the role of base is played by ITX radical anion formed in situ by a primary photoinduced electron‐transfer reaction between electronically excited ITX (oxidant) and BPh4− (reductant). An NHC yield as high as 70 % is achieved upon starting with a stoichiometric ratio of ITX and azolium salt. Three different photoNHC‐mediated polymerizations are described: synthesis of polyurethane and polyester by organocatalyzed step‐growth polymerization and ring‐opening copolymerization, respectively, and generation of polynorbornene by ring‐opening metathesis polymerization using an NHC‐coordinated Ru catalyst formed in situ.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Mixture of Azolium Tetraphenylborate with Isopropylthioxanthone: A New Class of N‐Heterocyclic Carbene (NHC) Photogenerator for Polyurethane, Polyester, and ROMP Polymers Synthesis

Trinh

Malval

Morlet‐Savary

et al. 2019

Chemistry A European J

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“…The widespread utility of these durable high-strength materials is manifested from the various applications in the form of fibers, industrial yarns, floor covering and engineering plastics or films. [21][22][23][24][25][26][27][28][29] In addition to intense energy requirements, these high-temperature reactions have several other drawbacks, including the formation of undesired side products. [2] With the increase in environmental regulation toward reduction of industrial energy consumption and carbon dioxide (CO 2 ) emission, significant efforts are being made to develop a greener and more efficient technology for making nylon.…”

mentioning

confidence: 99%

“…[2] With the increase in environmental regulation toward reduction of industrial energy consumption and carbon dioxide (CO 2 ) emission, significant efforts are being made to develop a greener and more efficient technology for making nylon. [21][22][23][24][25][26][27][28][29] In addition to intense energy requirements, these high-temperature reactions have several other drawbacks, including the formation of undesired side products. [11][12][13][14][15][16][17][18][19][20] Buchmeiser et al reported a series of N-heterocyclic carbenes (NHCs) as initiators at temperatures of 180-200°C for anionic ring-opening homo as well as copolymerization of lactams to give corresponding polyamide PA 12 and PA 6/12.…”

mentioning

confidence: 99%

Polymerization of ϵ‐Caprolactam to Nylon‐6 Catalyzed by Barium σ‐Borane Complex under Mild Condition

Bhattacharjee

Harinath

Sarkar³

et al. 2019

ChemCatChem

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A mild and low-temperature synthesis of nylon-6 is achieved through the ring-opening polymerization of ɛ-caprolactam using barium σ-borane complex as the catalyst. Due to the mild nature of the catalyst, this protocol provides an easy means of synthesizing nylon-6, for the first time with a precise and predictable molecular weight. From various model experiments, it is evident that the σ-coordinated boron hydride acts as a mild hydride donor in the first step of the reaction to generate lactamate anions, which then undergo ring-opening polymerization in-situ with the remaining caprolactam molecules under the influence of the dehydrogenated boron metal complex.Polyamides are among the most versatile synthetic polymers and are indispensable to modern life. The widespread utility of these durable high-strength materials is manifested from the various applications in the form of fibers, industrial yarns, floor covering and engineering plastics or films. [1] Among all the polyamides available today, poly (ɛ-caprolactam) or nylon-6 alone represents approximately 45 % of worldwide production in terms of volume. [2] With the increase in environmental regulation toward reduction of industrial energy consumption and carbon dioxide (CO 2 ) emission, significant efforts are being made to develop a greener and more efficient technology for making nylon. [3][4][5][6][7][8][9][10] The industrial production of nylon-6 is commonly carried out by means of anionic polymerization, which is performed hydrolytically at 250°C or at a relatively lower temperature of 150°C in the presence of an initiator. [11][12][13][14][15][16][17][18][19][20] Buchmeiser et al. reported a series of N-heterocyclic carbenes (NHCs) as initiators at temperatures of 180-200°C for anionic ring-opening homo as well as copolymerization of lactams to give corresponding polyamide PA 12 and PA 6/12. [21][22][23][24][25][26][27][28][29] In addition to intense energy requirements, these high-temperature reactions have several other drawbacks, including the formation of undesired side products. The properties of nylon-6 synthesized through anionic polymerization are often shaped by irregularities in the polymer chain because of side reactions such as Claisen-type condensations that occur during the polymerization of ɛ-caprolactam. These side reactions are strongly marked by weak heat exchange with the surrounding medium during typical bulk polymerization. [30] Ricco et al. have studied the influence of fast activators on the chain regularity and polymorphism of synthesized nylon-6. [31] At the same time, cationic initiation is not as useful as its anionic counterparts because of poor conversion and low molecular weight of the resultant polymer.Furthermore, while the use of an alkali or alkaline metal or alkali metal hydride enables the synthesis of nylon-6 in good proportion, the side reactions adulterate the product with amines and water, which destroy reactive initiator and propagate a species that often promotes polymer branching and chain irregularities. Therefo...

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