Phenoxyimine Ligands Bearing Nitrogen-Containing Second Coordination Spheres for Zinc Catalyzed Stereoselective Ring-Opening Polymerization of <i>rac</i>-Lactide

Li, Min; Behzadi, Shabnam; Chen, Min; Pang, Wenmin; Wang, Fuzhou; Tan, Chen

doi:10.1021/acs.organomet.8b00788

Cited by 15 publications

(24 citation statements)

References 57 publications

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“…There is no doubt that the metal-based catalysts are dominant in the polymerization catalysis area, given their varying combinations of ligands and metals. In the past decades, a variety of aluminum, − magnesium and zinc, − iron, titanium, and zirconium, − and rare-earth-metal − complexes have been employed for the preparation of polyesters. Among these, Al complexes ligating ancillary ligands have gained considerable attention and have become promising candidates for ROP reactions due to their high activity, relatively low toxicity, and good control of the molecular weight (MW) and dispersity ( Đ = M w / M n ) of the resulting polyesters .…”

Section: Introductionmentioning

confidence: 99%

Aluminum Complexes Bearing Bidentate Amido–Phosphine Ligands for Ring-Opening Polymerization of ε-Caprolactone: Steric Effect on Coordination Chemistry and Reactivity

et al. 2019

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The aluminum complexes LAlMe2 (Al1–Al5: LH = 2,6-(R1)2-4-R2-C6H2NHCH2C6H4-2-PPh2; Al1, R1 = H, R2 = H; Al2, R1 = Me, R2 = H; Al3, R1 = i Pr, R2 = H; Al4, R1 = Ph2CH, R2 = i Pr; Al5, R1 = Cl, R2 = H) have been synthesized and characterized by elemental analysis and 1H, 13C, and 31P NMR. NMR analysis in solution reveals an interesting hemilabile coordination of the soft P donor. The molecular structures of Al2–Al4 were defined by X-ray diffraction studies, showing a distorted-tetrahedral geometry around the aluminum center in all structures. Careful comparison of these crystal structures suggested that different substituents on the ligands could lead to unignorable changed coordination environments around the Al center, thus affecting their catalytic properties. In the presence of BnOH, complexes Al1–Al5 efficiently catalyzed the ring-opening polymerization (ROP) of ε-caprolactone (ε-CL) with high conversions in a controlled manner, and high molecular weights (M n up to 118.6 kg mol–1) of polycaprolactones (PCLs) were readily prepared. Immortal polymerizations by Al4 having bulky Ph2CH groups were also studied with up to 20 equiv of alcohols and 2000 equiv of monomers, without sacrificing polymerization control.

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Section: Introductionmentioning

confidence: 99%

Aluminum Complexes Bearing Bidentate Amido–Phosphine Ligands for Ring-Opening Polymerization of ε-Caprolactone: Steric Effect on Coordination Chemistry and Reactivity

et al. 2019

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“…While ortho -2-imidazolylphenol ( L10 ) and ortho -pyrazolylphenol ( L11 ) did not outperform QNOL ligands, ortho -2-pyridinylphenol ( L12 ) gave the desired product in an improved 79% yield by GC-FID. Inspired by reports in the polymerization literature that phenoxyimine-based (FI) ligands performed similarly to QNOLs, the former class of ligands was explored for cobalt-catalyzed C(sp 2 )–C(sp 3 ) Suzuki-Miyaura cross-coupling. This ligand class has been previously studied in the context of cobalt-catalyzed C(sp 2 )–C(sp 2 ) Suzuki–Miyaura cross-coupling, and modest reactivity with yields up to 47% as judged by GC-MS using activated lithium borate nucleophiles was reported …”

Section: Resultsmentioning

confidence: 99%

Cobalt-Catalyzed C(sp²)–C(sp³) Suzuki–Miyaura Cross-Coupling Enabled by Well-Defined Precatalysts with L,X-Type Ligands

et al. 2022

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Cobalt(II) halides in combination with phenoxyimine (FI) ligands generated efficient precatalysts in situ for the C(sp2)–C(sp3) Suzuki–Miyaura cross-coupling between alkyl bromides and neopentylglycol (hetero)arylboronic esters. The protocol enabled efficient C–C bond formation with a host of nucleophiles and electrophiles (36 examples, 34–95%) with precatalyst loadings of 5 mol %. Studies with alkyl halide electrophiles that function as radical clocks support the intermediacy of alkyl radicals during the course of the catalytic reaction. The improved performance of the FI–cobalt catalyst was correlated with decreased lifetimes of cage-escaped radicals as compared to those of diamine-type ligands. Studies of the phenoxyimine–cobalt coordination chemistry validate the L,X interaction leading to the discovery of an optimal, well-defined, air-stable mono-FI–cobalt(II) precatalyst structure.

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“…More recently, zinc complexes supported by the anionic phenoxyimine ligands were also used in the ring-opening polymerization of lactide. 17 Despite the good catalytic performance, these zinc complexes and other ones supported by anionic spectator ligands are inherently sensitive to air, moisture, and potential protic impurities in the monomer feedstock. This necessitates polymerizations under stringent inert conditions with sublimed lactide, typically not used in commercial reactors.…”

Section: ■ Introductionmentioning

confidence: 99%

“…Bulky substituents on the β-diiminate were shown to enhance activities, further demonstrating the value of coordinating easily prepared tunable spectator ligands. More recently, zinc complexes supported by the anionic phenoxyimine ligands were also used in the ring-opening polymerization of lactide . Despite the good catalytic performance, these zinc complexes and other ones supported by anionic spectator ligands are inherently sensitive to air, moisture, and potential protic impurities in the monomer feedstock.…”

Section: Introductionmentioning

confidence: 99%

Lactide Polymerization Using Zinc Dichloride Complexes Containing a Neutral Bidentate Ligand with a Diacylated Cyclic Guanidine

et al. 2022

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Zinc complexes of neutral bidentate ligands that contain an electron-poor diacylated cyclic guanidine are reported, along with their reactivity in solvent-free polymerization of rac-lactide. The diacyl groups significantly decrease the electron-donating ability of the ligand compared to the corresponding nonacylated derivative. This manifested itself through restricted rotation about the formal C−N exo double bond, with the Gibbs free-energy rotational barrier (ΔG ‡) ranging from 47.4 to 59.6 kJ mol −1 . Restricted rotation was also observed for the isopropyl substituent syn to the N exo aryl ring with ΔG ‡ values of 47.5−51.9 kJ mol −1 . Coordination of the ligands to zinc caused further π-electron delocalization from the endocyclic to the exocyclic nitrogen, thereby decreasing the Wiberg bond index of the C−N exo bond from 1.67−1.70 to 1.48−1.50 and eliminating all restricted rotations at room temperature. All three complexes were active in the solvent-free polymerization of rac-lactide with the second-order polymerization rate constant for the anthranilate-based complex of 7.30 × 10 −3 M −1 s −1 . The resulting polymers had a slight heterotactic bias (P r = 0.60) with molecular weights lower than anticipated, possibly due to transesterification, as suggested by mass spectrometry. The mass spectrum of the polymer did not show evidence of the ligand dissociating from the metal during the initiation step and its incorporation into the polymer structure. The acylation of the cyclic guanidine thus imparts advantages to the ligand, with the second building block offering additional opportunities to further improve the catalytic performance of these zinc complexes.

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Phenoxyimine Ligands Bearing Nitrogen-Containing Second Coordination Spheres for Zinc Catalyzed Stereoselective Ring-Opening Polymerization of rac-Lactide

Cited by 15 publications

References 57 publications

Aluminum Complexes Bearing Bidentate Amido–Phosphine Ligands for Ring-Opening Polymerization of ε-Caprolactone: Steric Effect on Coordination Chemistry and Reactivity

Aluminum Complexes Bearing Bidentate Amido–Phosphine Ligands for Ring-Opening Polymerization of ε-Caprolactone: Steric Effect on Coordination Chemistry and Reactivity

Cobalt-Catalyzed C(sp²)–C(sp³) Suzuki–Miyaura Cross-Coupling Enabled by Well-Defined Precatalysts with L,X-Type Ligands

Lactide Polymerization Using Zinc Dichloride Complexes Containing a Neutral Bidentate Ligand with a Diacylated Cyclic Guanidine

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Phenoxyimine Ligands Bearing Nitrogen-Containing Second Coordination Spheres for Zinc Catalyzed Stereoselective Ring-Opening Polymerization of rac-Lactide

Cited by 15 publications

References 57 publications

Aluminum Complexes Bearing Bidentate Amido–Phosphine Ligands for Ring-Opening Polymerization of ε-Caprolactone: Steric Effect on Coordination Chemistry and Reactivity

Aluminum Complexes Bearing Bidentate Amido–Phosphine Ligands for Ring-Opening Polymerization of ε-Caprolactone: Steric Effect on Coordination Chemistry and Reactivity

Cobalt-Catalyzed C(sp2)–C(sp3) Suzuki–Miyaura Cross-Coupling Enabled by Well-Defined Precatalysts with L,X-Type Ligands

Lactide Polymerization Using Zinc Dichloride Complexes Containing a Neutral Bidentate Ligand with a Diacylated Cyclic Guanidine

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Cobalt-Catalyzed C(sp²)–C(sp³) Suzuki–Miyaura Cross-Coupling Enabled by Well-Defined Precatalysts with L,X-Type Ligands