Ultrarapid Cerium(III)–NHC Catalysts for High Molar Mass Cyclic Polylactide

Kerr, Ryan W. F.; Ewing, Paul M. D. A.; Raman, Sumesh K.; Smith, Andrew D.; Williams, Charlotte K.; Arnold, Polly L.

doi:10.1021/acscatal.0c04858

Cited by 33 publications

(45 citation statements)

References 48 publications

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“…41,44 In particular, the recent use of metal catalysts with NHC ligands has led to incredibly fast, controlled polymerizations, which is another advantage considering the lengthy reaction times involved in ring closure approaches. 45,46 While rapid progress has been made in the synthesis of cyclic polymers over the past decade, some synthetic questions remain. For instance, the possibility of catenanes being produced in these polymerizations has yet to be discussed in depth to our knowledge.…”

Section: ■ Scope Of Reviewmentioning

confidence: 99%

Synthesis, Properties, and Applications of Bio-Based Cyclic Aliphatic Polyesters

et al. 2021

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Cyclic polymers have long been reported in the literature, but their development has often been stunted by synthetic difficulties such as the presence of linear contaminants. Research into the synthesis of these polymers has made great progress in the past decade, and this review covers the synthesis, properties, and applications of cyclic polymers, with an emphasis on bio-based aliphatic polyesters. Synthetic routes to cyclic polymers synthesized from bioderived monomers, alongside mechanistic descriptions for both ring closure and ring expansion polymerization approaches, are reviewed. The review also highlights some of the unique physical properties of cyclic polymers together with potential applications. The findings illustrate the substantial recent developments made in the syntheses of cyclic polymers, as well as the progress which can be made in the commercialization of bio-based polymers through the versatility this topology provides.

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Section: ■ Scope Of Reviewmentioning

confidence: 99%

Synthesis, Properties, and Applications of Bio-Based Cyclic Aliphatic Polyesters

et al. 2021

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“…However, this weak bond may be enhanced by harnessing anionic linkers. This strategy has allowed the isolation of a number of interesting metal complexes − of the early transition metals, − the lanthanides, − and the actinides. − …”

Section: Introductionmentioning

confidence: 99%

Mesoionic Carbenes in Low- to High-Valent Vanadium Chemistry

et al. 2021

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We report the synthesis of vanadium(V) oxo complex 1 with a pincer-type dianionic mesoionic carbene (MIC) ligand L 1 and the general formula [VOCl(L 1 )]. A comparison of the structural (SC-XRD), electronic (UV–vis), and electrochemical (cyclic voltammetry) properties of 1 with the benzimidazolinylidene congener 2 (general formula [VOCl(L 2 )]) shows that the MIC is a stronger donor also for early transition metals with low d-electron population. Since electrochemical studies revealed both complexes to be reversibly reduced, the stronger donor character of MICs was not only demonstrated for the vanadium(V) but also for the vanadium(IV) oxidation state by isolating the reduced vanadium(IV) complexes [Co(Cp*) 2 ][1] and [Co(Cp*) 2 ][2] ([Co(Cp*) 2 ] = decamethylcobaltocenium). The electronic structures of the compounds were investigated by computational methods. Complex 1 was found to be a moderate precursor for salt metathesis reactions, showing selective reactivity toward phenolates or secondary amides, but not toward primary amides and phosphides, thiophenols, or aryls/alkyls donors. Deoxygenation with electron-rich phosphines failed to give the desired vanadium(III) complex. However, treatment of the deprotonated ligand precursor with vanadium(III) trichloride resulted in the clean formation of the corresponding MIC vanadium(III) complex 6 , which undergoes a clean two-electron oxidation with organic azides yielding the corresponding imido complexes. The reaction with TMS-N 3 did not afford a nitrido complex, but instead the imido complex 10 . This study reveals that, contrary to popular belief, MICs are capable of supporting early transition-metal complexes in a variety of oxidation states, thus making them promising candidates for the activation of small molecules and redox catalysis.

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“…The controlled ring-opening polymerization (ROP) of lactide by single-site metal coordination catalysts is an important method to produce polymers of high molecular weight, narrow polydispersity, and controlled microstructure . Recently, Arnold and co-workers reported that trivalent yttrium and cerium complexes featuring NHC tethered to an anionic group catalyzed the ROP of lactide to produce linear and cyclic PLA, respectively. , Herein, we aimed to study the catalytic behaviors of NHC-stabilized divalent lanthanide bis(amido) complexes and preliminarily investigate the influence of the ionic radii and types of NHCs. Complexes 2Ln can catalyze the ROP of rac -LA (Table , entries 1–3) with moderate molecular weights ( M n = 18.7–23.2 kDa) and narrow molecular weight distributions (PDI = 1.16–1.24).…”

Section: Resultsmentioning

confidence: 99%

Synthesis and Reactivity of N-heterocyclic Carbene Stabilized Lanthanide(II) Bis(amido) Complexes

et al. 2021

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Lanthanide amides are some of the most important reagents and catalysts in lanthanide organometallic chemistry because of their high stability. Nevertheless, the readily available homoleptic Ln[N(SiMe 3 ) 2 ] n (n = 2, 3) complexes lack feasible strategies to modulate their reactivity and selectivity. In this paper, monodentate N-heterocyclic carbenes (NHCs) were applied to synthesize the divalent lanthanide bis(amido) adducts 3,4Sm and 2− 4,7,8Eu. σ-bond metathesis reactions of (IiPr) 2 Yb[N(SiMe 3 ) 2 ] 2 (2Yb; IiPr = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene) with alkyne, aniline, and phenol yielded alkynyl-bridged [(IiPr)Yb[N-(SiMe 3 ) 2 ](μ-CCtBu)] 2 (9), monomeric (IiPr) 2 Yb[N(SiMe 3 ) 2 ]-(NHAr 1 ) (10; Ar 1 = 2,6-iPr 2 C 6 H 3 ), and (IiPr) 2 Yb(OAr 2 ) 2 (11; Ar 2 = 2,6-tBu 2 -4-MeC 6 H 2 ), respectively. All of the NHC adducts of lanthanide(II) complexes were structurally characterized by X-ray diffraction analysis. Moreover, 4Sm has high activity in the ROP of rac-LA without an alcohol initiator. Preliminary mechanism studies reveal that the ROP by 4Sm was initiated through a coordination−insertion mechanism, which involves electrophilic activation of the monomer by the metal center and nucleophilic attack of the amido group on the activated monomer. These studies demonstrate that the diverse NHCs could be potential ligands to not only suppress the ligand redistribution of heteroleptic Ln(II) complexes but also modulate the reactivity of lanthanide amide catalysts.

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Ultrarapid Cerium(III)–NHC Catalysts for High Molar Mass Cyclic Polylactide

Cited by 33 publications

References 48 publications

Synthesis, Properties, and Applications of Bio-Based Cyclic Aliphatic Polyesters

Synthesis, Properties, and Applications of Bio-Based Cyclic Aliphatic Polyesters

Mesoionic Carbenes in Low- to High-Valent Vanadium Chemistry

Synthesis and Reactivity of N-heterocyclic Carbene Stabilized Lanthanide(II) Bis(amido) Complexes

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