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Issue 20, 2017
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Highly thermally stable and robust enantiopure zirconium NNN-scorpionates for the controlled ring-opening polymerization of rac-lactide

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Abstract

A series of enantiopure alkoxide and thioalkoxide zirconium derivatives [Zr(ER)33-R,R-fbpza)] (1–6) (E = O, R = CHMe21, CHMeEt 2, CH2SiMe33, 2,6-C6H3Me24, 4-tBuPh 5; E = S, R = 4-tBuPh 6) has been prepared for use as thermally stable and robust initiators in the ROP of rac-lactide. The compounds were prepared by alcoholysis or thioalcoholysis of the tris(amide) precursor [Zr(NMe2)33-R,R-fbpza)] [R,R-fbpzaH = N-p-fluorophenyl-(1R)-1-[(1R)-6,6-dimethylbicyclo[3.1.1]-2-hepten-2-yl]-2,2-bis(3,5-dimethylpyrazol-1-yl)ethylamine] with ROH and ArEH (E = O, S) in a 1 : 3 molar ratio. The structures of the different compounds were determined by spectroscopic methods and, in addition, the X-ray crystal structure of 6 was also established. Interestingly, the tris(amide) precursor and complexes 2, 5, and 6 act as single-site living initiators for the well-controlled ring-opening polymerization of rac-lactide both in solution and in the melt. These processes produce polymers with medium molecular weights in good agreement with theoretical values and with narrow dispersity ranges. The activity of all initiators increased markedly with temperature and, more importantly, complex 2 exhibits the highest activity reported to date for a group 4-based initiator in the ROP of rac-LA under the industrially preferred melt and solvent-free conditions. Surprisingly, complex 2 is still highly active in the melt when using an unpurified monomer and it shows an unprecedented tolerance to water and impurities (49% conv., 15 min, 130 °C). Microstructural analysis of the poly(rac-lactide)s revealed a moderate heteroactivity in solution, with a Ps value of up to 0.70.

Graphical abstract: Highly thermally stable and robust enantiopure zirconium NNN-scorpionates for the controlled ring-opening polymerization of rac-lactide

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Publication details

The article was received on 23 Mar 2017, accepted on 20 Apr 2017 and first published on 20 Apr 2017


Article type: Paper
DOI: 10.1039/C7DT01050H
Citation: Dalton Trans., 2017,46, 6654-6662
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    Highly thermally stable and robust enantiopure zirconium NNN-scorpionates for the controlled ring-opening polymerization of rac-lactide

    A. Otero, J. Fernández-Baeza, A. Garcés, L. F. Sánchez-Barba, A. Lara-Sánchez, J. Martínez-Ferrer, M. P. Carrión and A. M. Rodríguez, Dalton Trans., 2017, 46, 6654
    DOI: 10.1039/C7DT01050H

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