Lithium calix[4]arenes: structural studies and use in the ring opening polymerization of cyclic esters

Redshaw, Carl; Yamato, Takehiko; Teat, Simon J.; Elsegood, Mark R. J.; Santoro, Orlando

Abstract

We have structurally characterized a number of lithiated calix[4]arenes, where the bridge in the calix[4]arene is thia (–S–, LS H4), sulfinyl (–SO–, LSOH4), sulfonyl (–SO2–, LSO2H4), dimethyleneoxa (–CH2OCH2–, LCOCH4) or methylene (–CH2–, LH4). In the case of L4SH4, interaction with LiOtBu led to the isolation of the complex [Li8(L4S)2(THF)4]5THF (15THF), whilst similar interaction of L4SOH4 led to the isolation of [Li6(L4SOH)2(THF)2]5(THF) (2$5THF). Interestingly, the mixed sulfinyl/sulfonyl complexes [Li8(calix[4] arene(SO)(SO2) SO1.68)2)2(THF)6]8(THF) (38THF) and
Li5Na(LSO/3SO2H)2(THF)5]7.5(THF) (47.5(THF) have also been characterized. Interaction of LiOtBu with LSO2H4 and LCOCH4 afforded [Li5L4SO2(OH)(THF)4]2THF (5$2THF) and [Li6(LCOC)2(HOtBu)2]0.78THF1.22hexane (60.78THF1.22hexane), respectively. In the case of LH4, reaction with LiOtBu in THF afforded a monoclinic polymorph [LH2Li2(thf)(OH2)2]3THF (73THF) of a known triclinic form of the complex, whilst reaction of the de-butylated analogue of LH4, namely de-BuLH4, afforded a polymeric chain structure {[Li5(de-BuL)(OH)(NCMe)3]2MeCN}n (82MeCN). For comparative catalytic studies, the complex [Li6(LPr)2(H2O)2]hexane (9 hexane), where LPr2H2 ¼ 1,3-di-n-propyloxycalix[4]areneH2, was also prepared. The molecular crystal structures of 1–9 are reported, and their ability to act as catalysts for the ring opening (co-)/polymerization (ROP) of the cyclic esters 3-caprolactone, d-valerolactone, and rac-lactide has been investigated. In most of the cases, complex 6 outperformed the other systems, allowing for higher conversions and/or greated polymer Mn.

Citation

Redshaw, C., Yamato, T., Teat, S. J., Elsegood, M. R. J., & Santoro, O. (2021). Lithium calix[4]arenes: structural studies and use in the ring opening polymerization of cyclic esters. RSC advances, 11(19), 11304-11317. https://doi.org/10.1039/d1ra00175b

• Journal Article Type: Article
• Acceptance Date: Mar 8, 2021
• Online Publication Date: Mar 17, 2021
• Publication Date: Mar 17, 2021
• Deposit Date: Mar 17, 2021
• Publicly Available Date: Mar 19, 2021
• Journal: RSC Advances
• Print ISSN: 2046-2069
• Electronic ISSN: 2046-2069
• Publisher: Royal Society of Chemistry
• Peer Reviewed: Peer Reviewed
• Volume: 11
• Issue: 19
• Pages: 11304-11317
• DOI: https://doi.org/10.1039/d1ra00175b
• Keywords: General Chemistry; General Chemical Engineering
• Public URL: https://hull-repository.worktribe.com/output/3741945