Highly thermally stable and robust enantiopure zirconium NNN-scorpionates for the controlled ring-opening polymerization of rac-lactide. Issue 20 (5th May 2017)

• Record Type: Journal Article
• Authors: Otero, Antonio; Fernández-Baeza, Juan; Garcés, Andrés; Sánchez-Barba, Luis F.; Lara-Sánchez, Agustín; Martínez-Ferrer, Jaime; Carrión, María P.; Rodríguez, Ana M.
• Is Part Of: Dalton transactions. Volume 46:Issue 20(2017)
• Page Start: 6654
• Page End: 6662
• Publication Date: 2017-05-05
• Subjects: Chemistry, Inorganic -- Periodicals; Chemistry, Physical and theoretical -- Periodicals; Chemistry, Inorganic -- Periodicals; 546.05
• DOI: 10.1039/c7dt01050h
• Languages: English
• ISSNs: 1477-9226

Abstract

Abstract : An enantiopure NNN-scorpionate zirconium alkoxide as the highest active group 4-based initiator in ROP of unpurified rac -LA under industrially preferred conditions. Abstract : A series of enantiopure alkoxide and thioalkoxide zirconium derivatives [Zr(ER)3 (κ 3 - R, R -fbpza)] (1–6 ) (E = O, R = CHMe2 1, CHMeEt2, CH2 SiMe3 3, 2, 6-C6 H3 Me2 4, 4- t BuPh5 ; E = S, R = 4- t BuPh6 ) 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 )3 (κ 3 - R, R -fbpza)] [ R, R -fbpzaH = N-p -fluorophenyl-(1 R )-1-[(1 R )-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 of6 was also established. Interestingly, the tris(amide) precursor and complexes2, 5, and6 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, complex2 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, complex2 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 P s value of up to 0.70.