NDLI: Metal influence on the iso- and hetero-selectivity of complexes of bipyrrolidine derived salan ligands for the polymerisation of <i>rac</i>-lactide

Content Provider	Royal Society of Chemistry (RSC)
Author	Schäfer, Pascal M. Jones, Matthew D. Brady, Lauren Buchard, Antoine Woodman, Timothy J. McKeown, Paul Thomas, Lynne H. Mahon, Mary F. Lowe, John P.
Copyright Year	2015
Abstract	In this paper we have prepared a series of Ti(IV), Hf(IV) and Al(III) complexes based on bipyrrolidine salan pro-ligands. The Hf(IV) complexes have all been characterised in the solid-state, the chiral ligands coordinate to Hf(IV) in an α-cis manner whereas the meso ligand coordinates in a β-cis geometry. The Hf(IV) complexes are all active for the ROP of rac-lactide in the melt, with the fluxional meso complex affording a strong isotactic bias Pm = 0.84. As expected Hf(3)(OiPr)2 polymerised L-LA faster than rac-LA (kapp = 5.9 × 10−3 min−1vs. 3.8 × 10−3 min−1). For Ti(IV) complexes atactic PLA was formed. The salan pro-ligands have also been complexed to Al(III), and the novel Al–Me and Al-OiPr complexes were characterised in the solid and solution state. Al(1)(OiPr) was fluxional on the NMR timescale, whereas Al(3)(OiPr) was locked in solution with no exchange. Interestingly, the Al(III) complexes of 3H2 produce PLA with a very strong heterotactic bias Pr upto 0.87, whereas atactic PLA is produced with 1H2. For Al(3)(OiPr) a linear relationship is observed with Mn and conversion. Experiments with the addition of an equivalent of rac-LA to the selective initiators have also been performed and are discussed.
Starting Page	5034
Ending Page	5039
Page Count	6
File Format	HTM / HTML PDF
ISSN	20416520
Volume Number	6
Issue Number	8
Journal	Chemical Science
DOI	10.1039/c5sc01819f
Language	English
Publisher	Royal Society of Chemistry
Access Restriction	Subscribed
Subject Keyword	Tacticity Kapp Records PLA Ti Ligand Chirality Al Nuclear magnetic resonance Molecular geometry
Content Type	Text
Resource Type	Article
Subject	Chemistry

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