Chiral salan aluminium ethyl complexes and their application in lactide polymerization

H(ongzhi) Du, Aldrik Velders, Pieter J. Dijkstra, Jingru Sun, Zhiyuan Zhong, Xuesi Chen, Jan Feijen

Research output: Contribution to journalArticleAcademicpeer-review

142 Citations (Scopus)

Abstract

Synthetic routes to aluminium ethyl complexes supported by chiral tetradentate phenoxyamine (salan-type) ligands [Al(OC6H2(R-6-R-4)CH2)2{CH3N(C6H10)NCH3}-C2H5] (4, 7: R=H; 5, 8: R=Cl; 6, 9: R=CH3) are reported. Enantiomerically pure salan ligands 1–3 with (R,R) configurations at their cyclohexane rings afforded the complexes 4, 5, and 6 as mixtures of two diastereoisomers (a and b). Each diastereoisomer a was, as determined by X-ray analysis, monomeric with a five-coordinated aluminium central core in the solid state, adopting a cis-(O,O) and cis-(Me,Me) ligand geometry. From the results of variable-temperature (VT) 1H NMR in the temperature range of 220–335 K, 1H–1H NOESY at 220 K, and diffusion-ordered spectroscopy (DOSY), it is concluded that each diastereoisomer b is also monomeric with a five-coordinated aluminium central core. The geometry is intermediate between square pyramidal with a cis-(O,O), trans-(Me,Me) ligand disposition and trigonal bipyramidal with a trans-(O,O) and trans-(Me,Me) disposition. A slow exchange between these two geometries at 220 K was indicated by 1H–1H NOESY NMR. In the presence of propan-2-ol as an initiator, enantiomerically pure (R,R) complexes 4–6 and their racemic mixtures 7–9 were efficient catalysts in the ring-opening polymerization of lactide (LA). Polylactide materials ranging from isotactically biased (Pm up to 0.66) to medium heterotactic (Pr up to 0.73) were obtained from rac-lactide, and syndiotactically biased polylactide (Pr up to 0.70) from meso-lactide. Kinetic studies revealed that the polymerization of (S,S)-LA in the presence of 4/propan-2-ol had a much higher polymerization rate than (R,R)-LA polymerization (kSS/kRR=10.1).
Original languageUndefined
Pages (from-to)9836-9845
JournalChemistry: a European journal
Volume15
Issue number38
DOIs
Publication statusPublished - 2009

Keywords

  • Chirality
  • Aluminum
  • Polymerization
  • IR-72591
  • salan
  • METIS-262785
  • lactide

Cite this

Du, H(ongzhi) ; Velders, Aldrik ; Dijkstra, Pieter J. ; Sun, Jingru ; Zhong, Zhiyuan ; Chen, Xuesi ; Feijen, Jan. / Chiral salan aluminium ethyl complexes and their application in lactide polymerization. In: Chemistry: a European journal. 2009 ; Vol. 15, No. 38. pp. 9836-9845.
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title = "Chiral salan aluminium ethyl complexes and their application in lactide polymerization",
abstract = "Synthetic routes to aluminium ethyl complexes supported by chiral tetradentate phenoxyamine (salan-type) ligands [Al(OC6H2(R-6-R-4)CH2)2{CH3N(C6H10)NCH3}-C2H5] (4, 7: R=H; 5, 8: R=Cl; 6, 9: R=CH3) are reported. Enantiomerically pure salan ligands 1–3 with (R,R) configurations at their cyclohexane rings afforded the complexes 4, 5, and 6 as mixtures of two diastereoisomers (a and b). Each diastereoisomer a was, as determined by X-ray analysis, monomeric with a five-coordinated aluminium central core in the solid state, adopting a cis-(O,O) and cis-(Me,Me) ligand geometry. From the results of variable-temperature (VT) 1H NMR in the temperature range of 220–335 K, 1H–1H NOESY at 220 K, and diffusion-ordered spectroscopy (DOSY), it is concluded that each diastereoisomer b is also monomeric with a five-coordinated aluminium central core. The geometry is intermediate between square pyramidal with a cis-(O,O), trans-(Me,Me) ligand disposition and trigonal bipyramidal with a trans-(O,O) and trans-(Me,Me) disposition. A slow exchange between these two geometries at 220 K was indicated by 1H–1H NOESY NMR. In the presence of propan-2-ol as an initiator, enantiomerically pure (R,R) complexes 4–6 and their racemic mixtures 7–9 were efficient catalysts in the ring-opening polymerization of lactide (LA). Polylactide materials ranging from isotactically biased (Pm up to 0.66) to medium heterotactic (Pr up to 0.73) were obtained from rac-lactide, and syndiotactically biased polylactide (Pr up to 0.70) from meso-lactide. Kinetic studies revealed that the polymerization of (S,S)-LA in the presence of 4/propan-2-ol had a much higher polymerization rate than (R,R)-LA polymerization (kSS/kRR=10.1).",
keywords = "Chirality, Aluminum, Polymerization, IR-72591, salan, METIS-262785, lactide",
author = "H(ongzhi) Du and Aldrik Velders and Dijkstra, {Pieter J.} and Jingru Sun and Zhiyuan Zhong and Xuesi Chen and Jan Feijen",
year = "2009",
doi = "10.1002/chem.200900799",
language = "Undefined",
volume = "15",
pages = "9836--9845",
journal = "Chemistry: a European journal",
issn = "0947-6539",
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Chiral salan aluminium ethyl complexes and their application in lactide polymerization. / Du, H(ongzhi); Velders, Aldrik; Dijkstra, Pieter J.; Sun, Jingru; Zhong, Zhiyuan; Chen, Xuesi; Feijen, Jan.

In: Chemistry: a European journal, Vol. 15, No. 38, 2009, p. 9836-9845.

Research output: Contribution to journalArticleAcademicpeer-review

TY - JOUR

T1 - Chiral salan aluminium ethyl complexes and their application in lactide polymerization

AU - Du, H(ongzhi)

AU - Velders, Aldrik

AU - Dijkstra, Pieter J.

AU - Sun, Jingru

AU - Zhong, Zhiyuan

AU - Chen, Xuesi

AU - Feijen, Jan

PY - 2009

Y1 - 2009

N2 - Synthetic routes to aluminium ethyl complexes supported by chiral tetradentate phenoxyamine (salan-type) ligands [Al(OC6H2(R-6-R-4)CH2)2{CH3N(C6H10)NCH3}-C2H5] (4, 7: R=H; 5, 8: R=Cl; 6, 9: R=CH3) are reported. Enantiomerically pure salan ligands 1–3 with (R,R) configurations at their cyclohexane rings afforded the complexes 4, 5, and 6 as mixtures of two diastereoisomers (a and b). Each diastereoisomer a was, as determined by X-ray analysis, monomeric with a five-coordinated aluminium central core in the solid state, adopting a cis-(O,O) and cis-(Me,Me) ligand geometry. From the results of variable-temperature (VT) 1H NMR in the temperature range of 220–335 K, 1H–1H NOESY at 220 K, and diffusion-ordered spectroscopy (DOSY), it is concluded that each diastereoisomer b is also monomeric with a five-coordinated aluminium central core. The geometry is intermediate between square pyramidal with a cis-(O,O), trans-(Me,Me) ligand disposition and trigonal bipyramidal with a trans-(O,O) and trans-(Me,Me) disposition. A slow exchange between these two geometries at 220 K was indicated by 1H–1H NOESY NMR. In the presence of propan-2-ol as an initiator, enantiomerically pure (R,R) complexes 4–6 and their racemic mixtures 7–9 were efficient catalysts in the ring-opening polymerization of lactide (LA). Polylactide materials ranging from isotactically biased (Pm up to 0.66) to medium heterotactic (Pr up to 0.73) were obtained from rac-lactide, and syndiotactically biased polylactide (Pr up to 0.70) from meso-lactide. Kinetic studies revealed that the polymerization of (S,S)-LA in the presence of 4/propan-2-ol had a much higher polymerization rate than (R,R)-LA polymerization (kSS/kRR=10.1).

AB - Synthetic routes to aluminium ethyl complexes supported by chiral tetradentate phenoxyamine (salan-type) ligands [Al(OC6H2(R-6-R-4)CH2)2{CH3N(C6H10)NCH3}-C2H5] (4, 7: R=H; 5, 8: R=Cl; 6, 9: R=CH3) are reported. Enantiomerically pure salan ligands 1–3 with (R,R) configurations at their cyclohexane rings afforded the complexes 4, 5, and 6 as mixtures of two diastereoisomers (a and b). Each diastereoisomer a was, as determined by X-ray analysis, monomeric with a five-coordinated aluminium central core in the solid state, adopting a cis-(O,O) and cis-(Me,Me) ligand geometry. From the results of variable-temperature (VT) 1H NMR in the temperature range of 220–335 K, 1H–1H NOESY at 220 K, and diffusion-ordered spectroscopy (DOSY), it is concluded that each diastereoisomer b is also monomeric with a five-coordinated aluminium central core. The geometry is intermediate between square pyramidal with a cis-(O,O), trans-(Me,Me) ligand disposition and trigonal bipyramidal with a trans-(O,O) and trans-(Me,Me) disposition. A slow exchange between these two geometries at 220 K was indicated by 1H–1H NOESY NMR. In the presence of propan-2-ol as an initiator, enantiomerically pure (R,R) complexes 4–6 and their racemic mixtures 7–9 were efficient catalysts in the ring-opening polymerization of lactide (LA). Polylactide materials ranging from isotactically biased (Pm up to 0.66) to medium heterotactic (Pr up to 0.73) were obtained from rac-lactide, and syndiotactically biased polylactide (Pr up to 0.70) from meso-lactide. Kinetic studies revealed that the polymerization of (S,S)-LA in the presence of 4/propan-2-ol had a much higher polymerization rate than (R,R)-LA polymerization (kSS/kRR=10.1).

KW - Chirality

KW - Aluminum

KW - Polymerization

KW - IR-72591

KW - salan

KW - METIS-262785

KW - lactide

U2 - 10.1002/chem.200900799

DO - 10.1002/chem.200900799

M3 - Article

VL - 15

SP - 9836

EP - 9845

JO - Chemistry: a European journal

JF - Chemistry: a European journal

SN - 0947-6539

IS - 38

ER -