Photoswitchable NHC-promoted ring-opening polymerizations

Neilson, Bethany M.; Bielawski, Christopher W.

doi:10.1039/c3cc42424c

Cited by 121 publications

(107 citation statements)

References 31 publications

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“…Although a variety of stimuli can be a priori envisioned for switchable catalysts, mostly redox chemo‐switchable metal catalysts24–29 have been described for the ROP of cyclic esters, although one example of allosteric control by non‐redox chemical switching of a metal‐based catalyst has also been reported 30. Moreover, some examples using chemo‐switchable31 and photo‐switchable32 organocatalysts have recently appeared, the concept and modus operandi of which can, in principle, be extended to metal‐based catalysts. Hence, all of these different switchable ROP systems are described hereafter.…”

Section: Switchable Catalysismentioning

confidence: 99%

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Beyond Stereoselectivity, Switchable Catalysis: Some of the Last Frontier Challenges in Ring‐Opening Polymerization of Cyclic Esters

Guillaume

Kirillov

Sarazin

et al. 2015

Chemistry A European J

229

119

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Metal-based catalysts and initiators have played a pivotal role in the ring-opening polymerization (ROP) of cyclic esters, thanks to their high activity and remarkable ability to control precisely the architectures of the resulting polyesters in terms of molar mass, dispersity, microstructure, or tacticity. Today, after two decades of extensive research, the field is slowly reaching maturity. However, several challenges remain, while original concepts have emerged around new types or new applications of catalysis. This Review is not intended to comprehensively cover all of these aspects. Rather, it provides a personal overview of the very recent progress achieved in some selected, important aspects of ROP catalysis--stereocontrol and switchable catalysis. Hence, the first part addresses the development of new metal-based catalysts for the isoselective ROP of racemic lactide towards stereoblock copolymers, and the use of syndioselective ROP metal catalysts to control the monomer sequence in copolymers. A second part covers the development of ROP catalysts--primarily metal-based catalysts, but also organocatalysts--that can be externally regulated by the use of chemical or photo stimuli to switch them between two states with different catalytic abilities. Current challenges and opportunities are highlighted.

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Section: Switchable Catalysismentioning

confidence: 99%

“…However, the use of photochemical switches remains essentially unexplored in cyclic ester ROP catalysis. To our knowledge, there is no such example with a metal‐based ROP catalyst and the only report consists in a photoswitchable organocatalyst reported by Neilson and Bielawski in 2013 32…”

Section: Switchable Catalysismentioning

confidence: 99%

Beyond Stereoselectivity, Switchable Catalysis: Some of the Last Frontier Challenges in Ring‐Opening Polymerization of Cyclic Esters

Guillaume

Kirillov

Sarazin

et al. 2015

Chemistry A European J

229

119

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“…[1] An attractive class of substrates for incorporating lightresponsive groups are the N-heterocyclic carbenes (NHCs) as they have been used in ab road range of organometallic and organocatalysts. [7] Similarly,aRh catalyst bearing the same NHC was found to catalyze hydroborations. [3] We recently developed ap hotoswitchable NHC by incorporating ap hotochromic [4] dithienylethene (DTE) [5] unit into an imidazolylidene backbone,and found that the corresponding carbene functioned as ap hotoswitchable organocatalyst for transesterification and transamidation [6] reactions as well as for ring-opening polymerizations.…”

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confidence: 99%

An Isolable, Photoswitchable N‐Heterocyclic Carbene: On‐Demand Reversible Ammonia Activation

et al. 2015

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The first isolable, photoswitchable N-heterocyclic carbene was synthesized and found to undergo reversible electrocyclic isomerization upon successive exposure to UV and visible radiation. The UV-induced ring closure afforded substantial changes to the electronic structure of the dithienylethene-based NHC, as evidenced by changes in the corresponding UV/Vis absorption and (13)C NMR spectra. Likewise, molecular orbital calculations revealed diminished electron density at the carbene nucleus upon photocyclization, consistent with the enhanced electrophilicity displayed by the ring-closed form. The photoswitchable NHC was successfully switched between its ring-opened and ring-closed states with high fidelity over multiple cycles. Furthermore, the ring-closed isomer was found to undergo facile N-H bond activation, allowing for the controlled capture and release of ammonia upon cycling between its isomeric states.

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“…Recent developments have focused on the latent ROP of cyclic esters to yield the desired polyesters, the majority of the examples again based on NHCs. Bielawski and Neilson presented a UV‐switchable NHC, where a change of light source induced a cyclization or opening of the NHC backbone . This results in a considerable change of electron density at the carbene center, rendering imidazolium derivative 15 active for the ROP of δ ‐valeroclactone and ε‐caprolactone in the presence of benzylic alcohol as co‐initiator, while derivative 16 is strongly deactivated ( k 15 / k 16 = 59, Scheme ).…”

Section: Polyestersmentioning

confidence: 99%

“…Preparation of a polyester by a photoswitchable NHC. UV irradiation entails formation of a large conjugated system, rendering 16 almost inactive …”

Section: Polyestersmentioning

confidence: 99%

Latent and Delayed Action Polymerization Systems

Naumann

Buchmeiser

2014

Macromol. Rapid Commun.

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Various approaches to latent polymerization processes are described. In order to highlight recent advances in this field, the discussion is subdivided into chapters dedicated to diverse classes of polymers, namely polyurethanes, polyamides, polyesters, polyacrylates, epoxy resins, and metathesis-derived polymers. The described latent initiating systems encompass metal-containing as well as purely organic compounds that are activated by external triggers such as light, heat, or mechanical force. Special emphasis is put on the different chemical venues that can be taken to achieve true latency, which include masked N-heterocyclic carbenes, latent metathesis catalysts, and photolatent radical initiators, among others. Scientific challenges and the advantageous application of latent polymerization processes are discussed.

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Photoswitchable NHC-promoted ring-opening polymerizations

Cited by 121 publications

References 31 publications

Beyond Stereoselectivity, Switchable Catalysis: Some of the Last Frontier Challenges in Ring‐Opening Polymerization of Cyclic Esters

Beyond Stereoselectivity, Switchable Catalysis: Some of the Last Frontier Challenges in Ring‐Opening Polymerization of Cyclic Esters

An Isolable, Photoswitchable N‐Heterocyclic Carbene: On‐Demand Reversible Ammonia Activation

Latent and Delayed Action Polymerization Systems

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