Lactide Polymerisation with Air‐Stable and Highly Active Zinc Complexes with Guanidine–Pyridine Hybrid Ligands

Börner, Janna; Flörke, Ülrich; Huber, Klaus; Döring, Artjom; Kuckling, Dirk; Herres‐Pawlis, Sonja

doi:10.1002/chem.200802128

Cited by 151 publications

(111 citation statements)

References 55 publications

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“…As initiating systems, a co-initiator, which can be benzyl alcohol or water, has the task of starting the polymerization catalyzed by the zinc guanidine complexes. In comparison to other zinc N,N-guanidine complexes, these systems show by far the highest activity in polymerization [65,69,70,72]. N gua ,O zinc chlorido complexes show the same reaction constants but yield polymers with molar masses, in good accordance with the theoretical ones, which demonstrates excellent reaction control [71].…”

Section: Polymerization Experimentssupporting

confidence: 69%

Reactivity of Zinc Halide Complexes Containing Camphor-Derived Guanidine Ligands with Technical rac-Lactide

et al. 2017

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Abstract:Three new zinc complexes with monoamine-guanidine hybridligands have been prepared, characterized by X-ray crystallography and NMR spectroscopy, and tested in the solvent-free ring-opening polymerization of rac-lactide. Initially the ligands were synthesized from camphoric acid to obtain TMGca and DMEGca and then reacted with zinc(II) halides to form zinc complexes. All complexes have a distorted tetrahedral coordination. They were utilized as catalysts in the solvent-free polymerization of technical rac-lactide at 150 • C. Colorless polylactide (PLA) can be produced and after 2 h conversion up to 60% was reached. Furthermore, one zinc chlorido complex was tested with different qualities of lactide (technical and recrystallized) and with/without the addition of benzyl alcohol as a co-initiator. The kinetics were monitored by in situ FT-IR or 1 H NMR spectroscopy. All kinetic measurements show first-order behavior with respect to lactide. The influence of the chiral complexes on the stereocontrol of PLA was examined. Moreover, with MALDI-ToF measurements the end-group of the obtained polymer was determined. DFT and NBO calculations give further insight into the coordination properties. All in all, these systems are robust against impurities and water in the lactide monomer and show great catalytic activity in the ROP of lactide.

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Section: Polymerization Experimentssupporting

confidence: 69%

Reactivity of Zinc Halide Complexes Containing Camphor-Derived Guanidine Ligands with Technical rac-Lactide

et al. 2017

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“…[41][42][43][44][45][46] For PYE-type compounds, conjugation between the pyridine and imine moieties suggests that, as ligands, these compounds could exhibit strong donation owing to a contribution of the pyridinium-amido resonance structure to the metal-ligand bond (B in Scheme 1). In this regard, a recent report by Johnson describes the selective nickel-mediated C À F activation of aryl fluorides by using isopropyl(1-methyl-1H-pyridin-4-ylidene)amine (Scheme 2) and direct comparison is made with strong donors such as N-heterocyclic carbenes (NHCs).…”

Section: Introductionmentioning

confidence: 98%

Synthesis, Coordination Chemistry and Bonding of Strong N‐Donor Ligands Incorporating the 1H‐Pyridin‐(2E)‐Ylidene (PYE) Motif

Qiu

Thatcher

Slattery

et al. 2009

Chemistry A European J

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A range of N-donor ligands based on the 1H-pyridin-(2E)-ylidene (PYE) motif have been prepared, including achiral and chiral examples. The ligands incorporate one to three PYE groups that coordinate to a metal through the exocyclic nitrogen atom of each PYE moiety, and the resulting metal complexes have been characterised by methods including single-crystal X-ray diffraction and NMR spectroscopy to examine metal-ligand bonding and ligand dynamics. Upon coordination of a PYE ligand to a proton or metal-complex fragment, the solid-state structures, NMR spectroscopy and DFT studies indicate that charge redistribution occurs within the PYE heterocyclic ring to give a contribution from a pyridinium-amido-type resonance structure. Additional IR spectroscopy and computational studies suggest that PYE ligands are strong donor ligands. NMR spectroscopy shows that for metal complexes there is restricted motion about the exocyclic C-N bond, which projects the heterocyclic N-substituent in the vicinity of the metal atom causing restricted motion in chelating-ligand derivatives. Solid-state structures and DFT calculations also show significant steric congestion and secondary metal-ligand interactions between the metal and ligand C-H bonds.

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“…Keywords: copolymerization · density functional calculations · P ligands · ring-opening polymerization · zinc works have involved the use of zinc complexes bearing a wider variety of anionic and neutral ligand frameworks, such as b-diketiminates, [21][22][23][24][25][26] phosphinimine, [27] guanidine-pyridine, [28] and tris(pyrazolyl)borates. [29] All of these ligands include nitrogen-based hard donor groups.…”

Section: Introductionmentioning

confidence: 99%

Coordination Chemistry and Reactivity of Zinc Complexes Supported by a Phosphido Pincer Ligand

D’Auria

Lamberti

Mazzeo

et al. 2012

Chemistry A European J

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The preparation and characterization of new Zn(II) complexes of the type [(PPP)ZnR] in which R = Et (1) or N(SiMe(3))(2) (2) and PPP is a tridentate monoanionic phosphido ligand (PPP-H = bis(2-diphenylphosphinophenyl)phosphine) are reported. Reaction of ZnEt(2) and Zn[N(SiMe(3))(2)](2) with one equivalent of proligand PPP-H produced the corresponding tetrahedral zinc ethyl (1) and zinc amido (2) complexes in high yield. Homoleptic (PPP)(2) Zn complex 3 was obtained by reaction of the precursors with two equivalents of the proligand. Structural characterization of 1-3 was achieved by multinuclear NMR spectroscopy ((1)H, (13)C, and (31)P) and X-ray crystallography (3). Variable-temperature (1)H and (31)P NMR studies highlighted marked flexibility of the phosphido pincer ligand in coordination at the metal center. A DFT calculation on the compounds provided theoretical support for this behavior. The activities of 1 and 2 toward the ring-opening polymerization of ε-caprolactone and of L- and rac-lactide were investigated, also in combination with an alcohol as external chain-transfer agent. Polyesters with controlled molecular parameters (M(n), end groups) and low polydispersities were obtained. A DFT study on ring-opening polymerization promoted by these complexes highlighted the importance of the coordinative flexibility of the ancillary ligand to promote monomer coordination at the reactive zinc center. Preliminary investigations showed the ability of these complexes to promote copolymerization of L-lactide and ε-caprolactone to achieve random copolymers whose microstructure reproduces the composition of the monomer feed.

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Lactide Polymerisation with Air‐Stable and Highly Active Zinc Complexes with Guanidine–Pyridine Hybrid Ligands

Cited by 151 publications

References 55 publications

Reactivity of Zinc Halide Complexes Containing Camphor-Derived Guanidine Ligands with Technical rac-Lactide

Reactivity of Zinc Halide Complexes Containing Camphor-Derived Guanidine Ligands with Technical rac-Lactide

Synthesis, Coordination Chemistry and Bonding of Strong N‐Donor Ligands Incorporating the 1H‐Pyridin‐(2E)‐Ylidene (PYE) Motif

Coordination Chemistry and Reactivity of Zinc Complexes Supported by a Phosphido Pincer Ligand

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