1. Improvement of catalytic activity of aluminum complexes for the ring-opening polymerization of ε-caprolactone: aluminum thioamidate and thioureidate systems.
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Ganta, Prasanna Kumar, Teja, Mallemadugula Ravi, Chang, Chun-Juei, Sambandam, Anandan, Kamaraj, Rajiv, Chu, Yu-Ting, Ding, Shangwu, Chen, Hsing-Yin, and Chen, Hsuan-Ying
- Subjects
RING-opening polymerization ,CATALYTIC activity ,ALUMINUM catalysts ,ALUMINUM ,DENSITY functional theory ,ACTIVATION energy - 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
Pr -Al exhibited a higher catalytic activity than OPr -Al (3.2 times as high for CL polymerization; [CL] : [SPr -Al] : [BnOH] = 100 : 0.5 : 2; [SPr -Al] = 10 mM, conv. = 93% after 14 min at 25 °C), and USCl -Al exhibited a higher catalytic activity than UCl -Al (4.6 times as high for CL polymerization; [CL] : [USCl -Al] : [BnOH] = 100 : 0.5 : 2; [USCl -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 [SPr -AlOMe2 ]2 decomposed into the four-membered ring SPr -AlOMe2 . However, [OPr -AlOMe2 ]2 did not decompose because of its strong bridging Al–O bond. The overall activation energy required for CL polymerization was lower when using [SPr -AlOMe2 ]2 (18.1 kcal mol−1 ) as a catalyst than when using [OPr -AlOMe2 ]2 (23.9 kcal mol−1 ). This is because the TS2a transition state of SPr -AlOMe2 had a more open coordination geometry with a small N–Al–S angle (72.91°) than did TS3c of [OPr -AlOMe2 ]2 , the crowded highest-energy transition state of [OPr -AlOMe2 ]2 with a larger N–Al–O angle (99.63°). [ABSTRACT FROM AUTHOR]- Published
- 2023
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