Electron rich (salen)AlCl catalysts for lactide polymerisation: Investigation of the influence of regioisomers on the rate and initiation efficiency

Rae, Annabel; Gaston, Anand J.; Greindl, Zoe; Garden, Jennifer A.

doi:10.1016/j.eurpolymj.2020.109917

Cited by 10 publications

(9 citation statements)

References 50 publications

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“…This supports the polymerization activity trend. Lastly, the k obs value of complex 4 (aniline) is smaller than 1 (3,4,5-trimethoxy) which suggests that ligands with electron donating groups on the Schiff-base ligand enhance the catalytic activity, which is in agreement with observations for ortho-OMe-substituted (salen)AlCl [34] End-group analysis was carried out using 1 H NMR spectroscopy and MALDI-TOF mass spectrometry (Figures 5 and 6). The 1 H NMR spectrum of the PCL produced by 1 (Table 3, entry 1) indicated the presence of one benzyl group (peaks k and m) and L 1 (peak g, f) group (Figure 5).…”

Section: Ring Opening Polymerization (Rop)supporting

confidence: 81%

Alkoxy-Functionalized Schiff-Base Ligation at Aluminum and Zinc: Synthesis, Structures and ROP Capability

et al. 2021

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The Schiff-base compounds 2,4-di-tert-butyl-6-(((3,4,5-trimethoxyphenyl)imino)methyl)phenol (L1H), 2,4-di-tert-butyl-6-(((2,4,6-trimethoxyphenyl)imino)methyl)phenol (L2H), 2,4-di-tert-butyl-6-(((2,4-trimethoxyphenyl)imino)methyl)phenol) (L3H) derived from anilines bearing methoxy substituents have been employed in the preparation of alkylaluminum and zinc complexes. Molecular structure determinations reveal mono-chelate aluminum complexes of the type [Al(Ln)(Me)2] (L1, 1; L2, 2; L3, 3), and bis(chelate) complexes for zinc, namely [Zn(Ln)2] (L1, 5; L2, 6; L3, 7). All complexes have significant activity at 50 °C and higher activity at 100 °C for the ring-opening polymerization (ROP) of ε-caprolactone (ε-CL) with good control over the molar mass distribution (Mw/Mn < 2) and molecular weight. Complex 1 was found to be the most active catalyst, achieving 99% conversion within 18 h at 50 °C and giving polycaprolactone with high molecular weight; results are compared against aniline-derived (i.e., non-methoxy containing) complexes (4 and 8). Aluminum or zinc complexes derived from L1 exhibit higher activity as compared with complexes derived from L2 and L3. Complex 1 was also tested as an initiator for the copolymerization of ε-CL and glycolide (GL). The CL-GL copolymers have various microstructures depending on the feed ratio. The crosslinker 4,4′-bioxepane-7,7′-dione was used in the polymerization with ε-CL using 1, and well-defined cross-linked PCL was afforded of high molecular weight.

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Section: Ring Opening Polymerization (Rop)supporting

confidence: 81%

Alkoxy-Functionalized Schiff-Base Ligation at Aluminum and Zinc: Synthesis, Structures and ROP Capability

et al. 2021

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“…The 1 H imine resonances of C1a – d correlate with the heterometal electropositivity (Figure S8), with an upfield shift relative to monometallic C1 (δ = 8.81 ppm; C1b , 8.43 ppm, χ Zn = 1.65; C1c , 8.40 ppm, χ Mg = 1.31; C1d , 8.24 ppm, χ Ca = 1.00; C1a , 8.20 ppm χ Li = 0.98). Incorporating a heterometal can thus modify the electronics of the complex, akin to the better explored use of electron-withdrawing/electron-donating ligand substituents to modulate catalyst activity in ROP. ,, Unfortunately, crystals of complexes C1 – C3 and C1a – d suitable for X-ray diffraction studies could not be obtained due to limited complex solubility.…”

Section: Resultsmentioning

confidence: 99%

“…Incorporating a heterometal can thus modify the electronics of the complex, akin to the better explored use of electron withdrawing/electron donating ligand substituents to modulate catalyst activity in ROP. 28,29,63 Unfortunately, crystals of complexes C1 and C1a-d suitable for X-ray diffraction studies could not be obtained due to limited complex solubility.…”

Section: Resultsmentioning

confidence: 99%

Cooperative Heterometallic Catalysts for Lactide Ring-Opening Polymerization: Combining Aluminum with Divalent Metals

et al. 2021

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While homometallic (salen)Al catalysts display excellent performance in lactide ring-opening polymerization (ROP), heterometallic (salen)Al complexes have yet to be reported. Herein, we describe four heterobimetallic (salen)Al catalysts and show that the choice of the heterometal is key. Cooperative Al/Mg and Al/Zn combinations improved the catalyst activity by a factor of up to 11 compared to the mono-Al analogue, whereas the mono-Mg and mono-Zn analogues were completely inactive. In contrast, Al/Li and Al/Ca heterocombinations stunted the polymerization rate. Kinetic and computational studies suggest that Al/Mg and Al/Zn cooperativity arises from the close intermetallic proximity facilitating chloride bridging (thus enhancing initiation), which promotes a rigid square pyramidal geometry around the Al center and further increases the available monomer coordination sites. This work also translates the use of ab initio molecular dynamics calculations to ROP, introducing a useful method of investigating catalyst flexibility and revealing that ligand strain and molecular rigidity can enhance heterometallic catalyst performance.

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“…66 Recently, the same o-vanillin ligands coordinated to Al(III) were reported for lactide ROP catalysis (TOF = 800 h −1 , 1 mol%, 120°C). 67 We have also reported bidentate o-vanillin Ti(IV) catalysts, coordinated by two chelating ligands, which showed very high rates in caprolactone ROP (CL ROP, TOF = 1800 h −1 , 0.5 mol%, 80°C). 68 Here, we target the effective tetradentate ortho-vanillin ligand for coordination with metal centres known to catalyse both lactone ROP and epoxide/anhydride ROCOP, i.e.…”

Section: Introductionmentioning

confidence: 91%

Ortho-vanillin derived Al(iii) and Co(iii) catalyst systems for switchable catalysis using ε-decalactone, phthalic anhydride and cyclohexene oxide

Diment

Stößer

Kerr

et al. 2021

Catal. Sci. Technol.

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Electron rich (salen)AlCl catalysts for lactide polymerisation: Investigation of the influence of regioisomers on the rate and initiation efficiency

Cited by 10 publications

References 50 publications

Alkoxy-Functionalized Schiff-Base Ligation at Aluminum and Zinc: Synthesis, Structures and ROP Capability

Alkoxy-Functionalized Schiff-Base Ligation at Aluminum and Zinc: Synthesis, Structures and ROP Capability

Cooperative Heterometallic Catalysts for Lactide Ring-Opening Polymerization: Combining Aluminum with Divalent Metals

Ortho-vanillin derived Al(iii) and Co(iii) catalyst systems for switchable catalysis using ε-decalactone, phthalic anhydride and cyclohexene oxide

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