Comparing a series of 8-quinolinolato complexes of aluminium, titanium and zinc as initiators for the ring-opening polymerization of rac-lactide

Abstract

The preparation and characterization of a series of 8-hydroxyquinoline ligands and their complexes with Ti(IV), Al(III) and Zn(II) centres is presented. The complexes are characterized using NMR spectroscopy, elemental analysis and, in some cases, by single crystal X-ray diffraction experiments. The complexes are compared as initiators for the ring-opening polymerization of racemic-lactide; all the complexes show moderate/good rates and high levels of polymerization control. In the case of the titanium or aluminium complexes, moderate iso-selectivity is observed (Pi = 0.75), whereas in the case of the zinc complexes, moderate hetero-selectivity is observed (Ps = 0.70).

Heterodinuclear titanium/zinc catalysis: synthesis, characterization and activity for CO2/epoxide copolymerization and cyclic ester polymerization

“…The selection of zinc was driven by the excellent precedent for zinc catalysts in CO 2 /CHO alternating copolymerization and in lactide or ε-caprolactone polymerizations. 30,[86][87][88][89][90][91][92][93][94][95] The addition of Et 2 Zn to a yellow solution of 2, in toluene, immediately formed a vivid orange solution (Scheme 1). Orange, block crystals were deposited from toluene solvent, after 24 hours at ambient temperature.…”

“…S11 and Table S2 †). [30][31][32][33] For example, 3 is 250 times faster, albeit at a higher concentration of monomer, than a related mono-titanium catalyst based on a diphenolate ligand scaffold (k obs = 16 × 10 −3 h −1 at 100°C, 1 mol% loading, [LA] -0.5 M in benzene, Fig. S11-E †).…”

Exploring Oxidation State-Dependent Selectivity in Polymerization of Cyclic Esters and Carbonates with Zinc(II) Complexes

“…Such interactions can be beneficial due to the hemilabile nature of the zinc-phosphine bond and may result in highly active polymerization systems. The use of redox-active ligands in combination with zinc for ring-opening polymerizations is even less common than the use of soft donor ligands despite the potential benefits ( Bakewell et al., 2015 ). Redox-active ligands provide a means of affecting the reactivity of the metal through changes in the oxidation state of the ligand.…”

ZnII Chlorido Complexes with Aliphatic, Chiral Bisguanidine Ligands as Catalysts in the Ring‐Opening Polymerisation of rac‐Lactide Using FT‐IR Spectroscopy in Bulk

“…Additionally, the tacticity can be controlled by these systems . Williams et al synthesised monozinc and dizinc catalysts containing bis(imino)diphenylamido ligands; these have outstanding activity . The high activity of these anionic ligand systems is often combined with a high sensitivity towards moisture, air and impurities in the monomer.…”