Redox-switchable ring-opening polymerization by tridentate ONN-type titanium and zirconium catalysts

Doerr, Alicia M.; Burroughs, Justin M.; Legaux, Nicholas M.; Long, Brian K.

doi:10.1039/d0cy00642d

Cited by 21 publications

(35 citation statements)

References 78 publications

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“…By way of example, catalyst 3 shows that the titanium metal center adopts a distorted octahedral geometry, surrounded by one ONN chelating ligand and three isopropoxide groups. The Ti–O(alkoxide) bond lengths of 1.844(3), 1.838(3), and 1.813(4) Å are typical for titanium alkoxides of this type, ,, with the longest bond length corresponding to the alkoxide trans to the ligand phenoxide and the shortest bond length corresponding to the alkoxide trans to the imine moiety. The longest bond length surrounding the metal center is the Ti–N(Me) 2 at 2.400(3) Å.…”

Section: Resultsmentioning

confidence: 99%

“…Closely related derivatives have been reported containing a two, rather than three, carbon atom bridge between the imine and amine. These molecules prefer the mer isomer in the solid state, indicating the length of the ligand arm may play a significant role in determining the overall structure in the solid state. , …”

Section: Resultsmentioning

confidence: 99%

“…Titanium alkoxide catalysts supported by phenoxy-imine-amine, or ONN-chelating ligands, have not been widely reported in the literature. However, catalysts supported by various tridentate ONN-chelates have been shown to facilitate both the formation and the degradation of PLA with zinc metal centers and recently have been used with group four metals in a redox-switchable system . In addition, the installation of the amine arm has the potential to facilitate interesting mechanistic abnormalities that augment the standard coordination-insertion mechanism.…”

Section: Introductionmentioning

confidence: 99%

“…However, catalysts supported by various tridentate ONN-chelates have been shown to facilitate both the formation and the degradation of PLA with zinc metal centers 20 and recently have been used with group four metals in a redox-switchable system. 21 In addition, the installation of the amine arm has the potential to facilitate interesting mechanistic abnormalities that augment the standard coordination-insertion mechanism. For example, labile amine arms have been used in aluminum complexes to explore the role of monomer binding.…”

Section: ■ Introductionmentioning

confidence: 99%

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Titanium ONN-(phenolate) Alkoxide Complexes: Unique Reaction Kinetics for Ring-Opening Polymerization of Cyclic Esters

et al. 2021

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The synthesis, characterization, and polymerization kinetics of four new titanium ONN-(phenolate) alkoxide catalysts were studied. Each catalyst is fluxional at room temperature, suggesting the ligand amine arm may be labile, but adopts a fac geometry in solution at low temperature (223 K) and in the solid state. All catalysts are active for the ring-opening polymerization of both ε-caprolactone (CL) and rac-lactide (LA). GPC analysis indicates that the well-known coordination-insertion mechanism is being followed. However, whereas the typical first-order dependence on monomer concentration is observed in CL, an unexpected zeroth-order dependence is observed with LA. This suggests that, in the case of LA, catalyst saturation occurs and a Michaelis−Menten model can be used to explain the kinetics. An initial mechanism is discussed within this model that proposes CL polymerization proceeds by a 7-coordinate intermediate, whereas LA polymerization adopts a 6-coordinate intermediate, facilitated by the ligand amine arm. Attempts to isolate catalyst-monomer intermediates are ongoing.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: ■ Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Titanium ONN-(phenolate) Alkoxide Complexes: Unique Reaction Kinetics for Ring-Opening Polymerization of Cyclic Esters

et al. 2021

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“…The latter feature was largely responsible for the extensive use of titanium and zirconium alkoxidos in catalysis [1,2]. The high polarity of M-OR bonds led to the application of several families of early transition metal complexes in the ring opening polymerization (ROP) of cyclic esters [3][4][5][6][7][8][9][10][11][12]. Our previous research on cyclam-based Zr(IV) alkoxido, phenoxido and thiophenoxido derivatives [13][14][15] also disclosed new catalytic systems for the ROP of rac-lactide strongly influenced by the nature of the OR ligands [13].…”

Section: Introductionmentioning

confidence: 99%

Synthesis and Characterization of New Cyclam-Based Zr(IV) Alkoxido Derivatives

Alves¹,

Martins

2021

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In this study, new mono- and di-alkoxido zirconium(IV) complexes supported by tetradentate dianionic cyclam ligands were synthesized and characterized. These compounds were obtained by reaction of the parent Zr(IV) dichlorido species with one or two equivalents of the corresponding lithium alkoxido, whereas (3,5-Me2Bn2Cyclam)Zr(OPh)2 was prepared by protonolysis of the orthometallated species (3,5-Me-C6H4CH2)2Cyclam)Zr with phenol. The solid-state molecular structures of (Bn2Cyclam)ZrCl(OtBu) and (4-tBuBn2Cyclam)Zr(OiPr)2 show a trigonal prismatic geometry around the metal centers. (Bn2Cyclam)Zr(SPh)(OtBu) and (Bn2Cyclam)ZrMe(OiPr) were prepared by reaction of (Bn2Cyclam)ZrCl(OR) (R = iPr, tBu) with one equivalent of LiSPh or MeMgCl, respectively. The reactions of (Bn2Cyclam)Zr(OiPr)2 and (4-tBuBn2Cyclam)Zr(OiPr)2 with carbon dioxide suggested the formation of species that correspond to the addition of four CO2 molecules.

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Redox‐Switchable Catalysis

Regenauer

Doll

Roşca

2022

Encyclopedia of Inorganic and Bioinorganic Chemistry

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The ability to control catalytic properties, such as selectivity and rate during the reaction, represents an attractive tool which can potentially deliver the synthesis of specialized products from a large pool of building blocks. This can be achieved by the incorporation of an on / off switch into the backbone of (pre‐)catalysts. The electronic or solubility properties of the switch can be then reversibly modified through the action of external triggers, a process which in turn modulates the catalytic activity. Incorporation of switches that can be reversibly reduced or oxidized represents one of the most versatile methods for controlling the catalytic activity in situ. This article describes the current state of research in the field of redox‐switchable catalysis, with a focus on homogenous metal‐mediated processes. The first part presents an overview of the types of redox switches and of the methods employed for delivering the redox stimuli. The second part then focuses on the catalytic transformations which can be controlled in this fashion, which include polymerization catalysis, metathesis, hydroelementation, and other catalytic reactions for the synthesis of fine chemicals.

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Redox-switchable ring-opening polymerization by tridentate ONN-type titanium and zirconium catalysts

Abstract: A study designed to ascertain the impact that ligand symmetry, number of redox-active moieties, and identity of the active metal center have on the catalytic ring-opening polymerization performance of redox-switchable catalysts.

Cited by 21 publications

References 78 publications

Titanium ONN-(phenolate) Alkoxide Complexes: Unique Reaction Kinetics for Ring-Opening Polymerization of Cyclic Esters

Titanium ONN-(phenolate) Alkoxide Complexes: Unique Reaction Kinetics for Ring-Opening Polymerization of Cyclic Esters

Synthesis and Characterization of New Cyclam-Based Zr(IV) Alkoxido Derivatives

Redox‐Switchable Catalysis

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