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Improvement of catalytic activity of aluminum complexes for the ring-opening polymerization of ε-caprolactone: aluminum thioamidate and thioureidate systems.
- Source :
- Dalton Transactions: An International Journal of Inorganic Chemistry; 12/14/2023, Vol. 52 Issue 46, p17132-17147, 16p
- Publication Year :
- 2023
-
Abstract
- In this study, a series of Al complexes bearing amidates, thioamidates, ureidates, and thioureidates were synthesized and their catalytic activity for ε-caprolactone (CL) polymerization was evaluated. S<superscript>Pr</superscript>-Al exhibited a higher catalytic activity than O<superscript>Pr</superscript>-Al (3.2 times as high for CL polymerization; [CL] : [S<superscript>Pr</superscript>-Al] : [BnOH] = 100 : 0.5 : 2; [S<superscript>Pr</superscript>-Al] = 10 mM, conv. = 93% after 14 min at 25 °C), and US<superscript>Cl</superscript>-Al exhibited a higher catalytic activity than U<superscript>Cl</superscript>-Al (4.6 times as high for CL polymerization; [CL] : [US<superscript>Cl</superscript>-Al] : [BnOH] = 100 : 0.5 : 2; [US<superscript>Cl</superscript>-Al] = 10 mM, conv. = 90% after 15 min at 25 °C). Regardless of whether aluminum amidates or ureidates were present, thioligands improved the polymerization rate of aluminum catalysts. Density functional theory calculations revealed that the eight-membered ring [S<superscript>Pr</superscript>-AlOMe<subscript>2</subscript>]<subscript>2</subscript> decomposed into the four-membered ring S<superscript>Pr</superscript>-AlOMe<subscript>2</subscript>. However, [O<superscript>Pr</superscript>-AlOMe<subscript>2</subscript>]<subscript>2</subscript> did not decompose because of its strong bridging Al–O bond. The overall activation energy required for CL polymerization was lower when using [S<superscript>Pr</superscript>-AlOMe<subscript>2</subscript>]<subscript>2</subscript> (18.1 kcal mol<superscript>−1</superscript>) as a catalyst than when using [O<superscript>Pr</superscript>-AlOMe<subscript>2</subscript>]<subscript>2</subscript> (23.9 kcal mol<superscript>−1</superscript>). This is because the TS2a transition state of S<superscript>Pr</superscript>-AlOMe<subscript>2</subscript> had a more open coordination geometry with a small N–Al–S angle (72.91°) than did TS3c of [O<superscript>Pr</superscript>-AlOMe<subscript>2</subscript>]<subscript>2</subscript>, the crowded highest-energy transition state of [O<superscript>Pr</superscript>-AlOMe<subscript>2</subscript>]<subscript>2</subscript> with a larger N–Al–O angle (99.63°). [ABSTRACT FROM AUTHOR]
Details
- Language :
- English
- ISSN :
- 14779226
- Volume :
- 52
- Issue :
- 46
- Database :
- Complementary Index
- Journal :
- Dalton Transactions: An International Journal of Inorganic Chemistry
- Publication Type :
- Academic Journal
- Accession number :
- 173894982
- Full Text :
- https://doi.org/10.1039/d3dt03198e