Highly selective and immortal magnesium calixarene complexes for the ring-opening polymerization of rac-lactide

Walton, Mark J.; Lancaster, Simon J.; Redshaw, Carl

Abstract

The lithiation of 1,3-dipropoxy-p-tert-butylcalix[4]arene (LH₂) followed by reaction with nBuMgBr in THF resulted in the formation of the hetero-bimetallic complex [Li(THF)Mg(nBu)L] (1). By contrast, the treatment of tripropoxy-p-tert-butylcalix[4]arene (L′H) with nBu₂Mg afforded a mononuclear complex [L′Mg(nBu)] (2). Single-crystal XRD studies revealed that in both structures the calix[4]arene adopts a cone conformation, and a Li cation resides in the cavity for 1. Both 1 and 2 were active for the ring-opening polymerisation of rac-lactide. Compound 2 displayed not only exceptional activity (100 equivalents, 3 min, 92 % conversion, BnOH, room temperature) but also high selectivity (probability to form an r dyad, Pᵣ=0.85) and exhibited an immortal character in THF. Surprisingly, compound 2 also showed isotactic bias (Pr=0.30–0.36) and an immortal character if toluene was employed as the solvent; 2 D J-resolved ¹H NMR spectroscopy was employed for the assignment of the stereoselectivity.

Citation

Walton, M. J., Lancaster, S. J., & Redshaw, C. (2014). Highly selective and immortal magnesium calixarene complexes for the ring-opening polymerization of rac-lactide. ChemCatChem, 6(7), 1892-1898. https://doi.org/10.1002/cctc.201402041

• Acceptance Date: Feb 12, 2014
• Online Publication Date: May 21, 2014
• Publication Date: 2014-07
• Deposit Date: Apr 22, 2015
• Publicly Available Date: Apr 22, 2015
• Journal: ChemCatChem
• Print ISSN: 1867-3880
• Publisher: Wiley
• Peer Reviewed: Peer Reviewed
• Volume: 6
• Issue: 7
• Pages: 1892-1898
• DOI: https://doi.org/10.1002/cctc.201402041
• Keywords: Calixarenes, Heterometallic complexes, Magnesium, NMR spectroscopy, Ring-opening polymerization
• Public URL: https://hull-repository.worktribe.com/output/372874
• Publisher URL: http://onlinelibrary.wiley.com/doi/10.1002/cctc.201402041/abstract
• Additional Information: This is the peer reviewed version of the following article: ChemCatChem, 2014, v.6, issue 7, which has been published in final form at http://dx.doi.org/10.1002/cctc.201402041. This article may be used for non-commercial purposes in accordance With Wiley-VCH Terms and Conditions for self-archiving.
• Contract Date: Apr 22, 2015