Well-controlled ring-opening polymerization of cyclic esters initiated by dialkylaluminum β-diketiminates

Li, Di; Peng, Ying; Geng, Chao; Liu, Kaipeng; Kong, Dexu

doi:10.1039/c3dt50372k

Cited by 69 publications

(26 citation statements)

References 43 publications

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“…Catalytic systems employing complexes 7 , 9 , 10 and 11 outperformed the others at 110 °C, affording quantitative conversions in 13 min or less. For complexes 1 – 6 , the trend is for the methyl derivatives to outperform the ethyl derivatives at both 80 and 100 °C, a trend that has been seen previously, the opposite trend has also been reported. [6u] Within the series 1 – 6 , on changing the sterics of the precursor aniline, there is little change in the conversion rates for either the methylaluminium or ethylaluminium derivatives.…”

Section: Resultssupporting

confidence: 69%

Organoaluminium Complexes Derived from Anilines or Schiff Bases for the Ring‐Opening Polymerization of ε‐Caprolactone, δ‐Valerolactone and rac‐Lactide

et al. 2017

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Reaction of R 1 R 2 CHN=CH(3,5-tBu 2 C 6 H 2 -OH-2) (R 1 = R 2 = Me L 1 H; R 1 = Me, R 2 = Ph L 2 H; R 1 = R 2 = Ph L 3 H) with slightly greater than one equivalent of R 3 3 Al (R 3 = Me, Et) afforded the complexes [(L 1-3 )AlR 3 2 ] (L 1 , R 3 = Me 1, R 3 = Et 2; L 2 , R 3 = Me 3, R 3 = Et 4; L 3 R 3 = Me 5, R 3 = Et 6); complex 1 has been previously reported. Use of the N,O-ligand derived from 2,2′-diphenylglycine afforded either 5 or the byproduct [Ph 2 NCH 2 (3,5-tBu 2 C 6 H 2 -O-2)AlMe 2 ] (7). The known Schiff base complex [2-Ph 2 PC 6 H 4 CH 2 (3,5-tBu 2 C 6 H 2 -O-2)AlMe 2 ] (8) and the product of the reaction of 2-diphenylphosphinoaniline 1-NH 2 ,2-PPh 2 C 6 H 4 with Me 3 Al, namely {Ph 2 PC 6 H 4 N[(Me 2 Al) 2 μ-Me]-(μ-Me 2 Al)} (9), were also isolated. For structural and catalytic comparisons, complexes resulting from the interaction of Me 3 Al with diphenylamine (or benzhydrylamine), namely {Ph 2 N[(Me 2 Al) 2 μ-Me]} (10) and [Ph 2 CHNH(μ-Me 2 Al)] 2 ·MeCN (11), were prepared. The molecular structures of the Schiff proligands derived from Ph 2 CHNH 2 and 2,2′-Ph 2 C(CO 2 H)(NH 2 ), together with those of complexes 5, 7 and 9-11·MeCN were determined; 5 contains a chelating imino/phenoxide ligand, whereas 7 contains the imino function outside of the metallocyclic ring. Complex 9 contains three nitrogen-bound Al centres, two of which are linked by a methyl bridge, whilst the [a] Scheme 1. Compounds (proligands) employed herein. Scheme 2. Complexes studied herein.1952 tBu 2 C 6 H 2 -O-2)AlR 3 2 ] (R 1 = R 2 = R 3 = Me 1; R 1 = R 2 = R 3 = Et 2; R 1 = R 3 = Me, R 2 = Ph 3; R 1 = Me, R 2 = Ph, R 3 = Et 4; R 1 = R 2 = Ph, R 3 = Me 5; R 1 = R 2 = Ph, R 3 = Et 6) and compare their behaviour against organoaluminium complexes derived from the amine component only (i.e., minus the phenoxy-containing 3,5-di-tert-butylsalicyl motif, see Schemes 1 and 2). We note that Nomura and colleagues have previously investigated the effect of the imino substituent on the ROP of ε-caprolactone (CL) and observed greatly enhanced activity for aryl substituents (C 6 F 5 , 2,6-iPr 2 C 6 H 3 ) versus aliphatic substituents (adamantyl, tert-butyl). [7] Herein, we initially targeted diphenylglycine (dpg) and derivatives thereof given the tendency of related motifs to form highly crystalline products. [9] However, the loss of CO 2 during the formation L 3 H(dpg), see discussion below, led us to explore the family of proligands with both aliphatic and aromatic substituents bound to the N-bound CH group.

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Section: Resultssupporting

confidence: 69%

Organoaluminium Complexes Derived from Anilines or Schiff Bases for the Ring‐Opening Polymerization of ε‐Caprolactone, δ‐Valerolactone and rac‐Lactide

et al. 2017

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“…The β ‐diketiminate aluminum ethyl complexes were unreactive toward isopropanol or benzyl alcohol even under violent reaction conditions, whereas the treatment of the amindinate aluminum complexes with isopropanol led to the release of free amindines. Similar results were also reported by Peng's group: for aluminum complexes bearing N‐alkyl substituted β ‐diketiminate ligands, the addition of benzyl alcohol led to the dissociation of the ligand from metal center. Therefore, aluminum complexes bearing multidentate ligands with only N‐donors, which are also capable of initiating the ROP of cyclic esters in a well‐controlled manner, are still less explored.…”

Section: Introductionsupporting

confidence: 88%

“…According to the literature reports, it is widely accepted that in comparison with ε −CL, lactide is in general less active toward the catalytic ROP, that is, longer reaction time or higher polymerization temperature is required for equal amount of lactide to be polymerized. It is also the case in this work.…”

Section: Resultsmentioning

confidence: 99%

Well‐controlled ring‐opening polymerization of cyclic esters catalyzed by aluminum amido complexes: Kinetics and mechanism

Liu

2014

J. Polym. Sci. Part A: Polym. Chem.

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A series of aluminum dimethyl complexes 1–6 bearing N‐[2‐(pyrrolidinyl)benzyl]anilido ligands were synthesized and well characterized. The molecular structure of complex 1 determined by an X‐ray diffraction study indicates the bidentate chelating mode of the pyrrolidinyl‐anilido ligand. In the absence of a coinitiator, these complexes exhibited excellent control toward the polymerizations of ε‐caprolactone and rac‐lactide, affording polyesters with quite narrow molecular weight distributions (Mw/Mn = 1.04–1.26). The end group analysis of ε−CL oligomer via 1H NMR and ESI‐TOF MS methods gave strong support to the hypothesis that the polymerization catalyzed by these aluminum complexes proceeds via a coordination‐insertion mechanism involving a unique AlN (amido) bond initiation. Via 1H NMR scale oligomerization studies, it is suggested that the insertion of the first lactide monomer into AlN bond of the complex is much easier than the insertion of lactide monomer into the newly formed AlO (lactate) bond and might also be easier than the insertion of the first ε−CL monomer into AlN bond. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 3096–3106

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“…These facts can best be explained by the concept that in a polar solvent the monomer is solvated thus the approach of the monomer towards attacking the cationic species is prevented. Thereby, the propagation of the polymer chain is hindered …”

Section: Resultsmentioning

confidence: 99%

Zwitterionic Complexes of Group 4 Metal Chlorides Containing a Bis(imino)phenoxide Scaffold: Synthesis, Characterization and Polymerization Studies

et al. 2016

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Chlorides of group 4 metals containing the bis(imino)phenoxide ligand scaffold were synthesized from a direct reaction between the respective ligand and metal chlorides MCl 4 (M = Ti, Zr and Hf). These complexes were thoroughly characterized using various spectroscopic methods and single crystal X-ray diffraction studies. They are potent catalysts for the polymerization of rac-lactide (rac-LA), L-lactide (L-LA), e-caprolactone (e-CL), epoxides such as, rac-cyclohexene oxide (rac-CHO), racpropylene oxide (rac-PO), rac-styrene oxide (rac-SO) and ethylene, resulting in polymers with high number average molecular weights (M n ) and narrow molecular weight distributions (MWDs). The kinetic and mechanistic studies associated with the polymerization of lactide, e-CL and CHO has been investigated in details.[a] Prof.

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Well-controlled ring-opening polymerization of cyclic esters initiated by dialkylaluminum β-diketiminates

Cited by 69 publications

References 43 publications

Organoaluminium Complexes Derived from Anilines or Schiff Bases for the Ring‐Opening Polymerization of ε‐Caprolactone, δ‐Valerolactone and rac‐Lactide

Organoaluminium Complexes Derived from Anilines or Schiff Bases for the Ring‐Opening Polymerization of ε‐Caprolactone, δ‐Valerolactone and rac‐Lactide

Well‐controlled ring‐opening polymerization of cyclic esters catalyzed by aluminum amido complexes: Kinetics and mechanism

Zwitterionic Complexes of Group 4 Metal Chlorides Containing a Bis(imino)phenoxide Scaffold: Synthesis, Characterization and Polymerization Studies

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