Journal
CHEMICAL SCIENCE
Volume 6, Issue 8, Pages 5034-5039Publisher
ROYAL SOC CHEMISTRY
DOI: 10.1039/c5sc01819f
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Funding
- EPSRC [EP/G03768X/1]
- EPSRC UK National Service for Computational Chemistry Software (chem752)
- Corbion
- University of Bath
- Engineering and Physical Sciences Research Council [1223532, EP/J003921/1] Funding Source: researchfish
- EPSRC [EP/J003921/1] Funding Source: UKRI
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In this paper we have prepared a series of Ti(IV), Hf(IV) and Al(III) complexes based on bipyrrolidine salan proligands. The Hf(IV) complexes have all been characterised in the solid-state, the chiral ligands coordinate to Hf(IV) in an alpha-cis manner whereas the meso ligand coordinates in a beta-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 P-m = 0.84. As expected Hf(3)(OPr)(2) polymerised L-LA faster than rac-LA (k(app) = 5.9 x 10(-3) min(-1) vs. 3.8 x 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)(OPr) was fluxional on the NMR timescale, whereas Al(3)((OPr)-Pr-i) was locked in solution with no exchange. Interestingly, the Al(III) complexes of 3H(2) produce PLA with a very strong heterotactic bias P-r upto 0.87, whereas atactic PLA is produced with 1H(2). For Al(3)(OPr) a linear relationship is observed with M-n and conversion. Experiments with the addition of an equivalent of rac-LA to the selective initiators have also been performed and are discussed.
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