Aluminium salophen and salen initiators in the ring-opening polymerisation of rac-lactide and rac-β-butyrolactone: Electronic effects on stereoselectivity and polymerisation rates

Abstract

The financial support of the Natural Sciences and Engineering Research Council of Canada, the Canada Foundation for Innovation, the Atlantic Canada Opportunities Agency and the Universities of Prince Edward Island and Edinburgh is acknowledged. We also thank Professor Rabin Bissessur for DSC analyses, Dr. Laura Allan for GPC analyses, Dr. Fabrice Berrue and Patricia Boland for ESI-MS analyses and Mr. Stephen Scully for NMR analyses.

Mechanistic Studies of ε-Caprolactone Polymerization by (salen)AlOR Complexes and a Predictive Model for Cyclic Ester Polymerizations

“…The X-ray structure ( Figure 2 ) confirms the anticipated five-coordinate formulation with a τ value of 0.84, 7 close to idealized trigonal bipyramidal (τ =1) and similar to that of related complexes of salen ligands also featuring the 2,2-dimethylpropyl linker. 4 , 8 The τ value differs from that previously determined for 1 (R = OMe; τ = 0.52) 6 and other closely related congeners with a two-carbon linker (τ = 0.48–0.56). 4 , 8a , 8b Density functional theory optimization of 2 (R = H; see Density Functional Calculations for theoretical details) provided a τ value of 0.85, which is in excellent agreement with that determined from crystallography, suggesting that crystal packing forces do not significantly influence the intrinsic coordination geometry at the aluminum center.…”

“…Such fluxionality was reported for other complexes of related salen ligands with the 2,2-dimethylpropyl linker. 4 , 8 The NMR spectra of the complexes 2 with different R groups are generally similar, except for differences in the aryl region (imine hydrogens and two aromatic hydrogens adjacent to R). The 27 Al NMR spectra contain a single resonance at 35, 34, and 33 ppm for the complexes with R = OMe, Br, NO 2 , respectively.…”

Exploiting Noncovalent Interactions for Room-Temperature Heteroselective rac-Lactide Polymerization Using Aluminum Catalysts

“…22 Interestingly, examples of Al complexes leading to highly heterotactic PLA (Pr > 0.80) are scarce and formation of isotactic PLA usually prevails. [25][26][27][28][29][30][31][32] Gibson and co-workers reported PLA with Pr up to 0.98 using an aluminium salan-type catalyst. 33 More recently, Jones and Kol separately reported a series of aluminium pyrolidine Schiff base catalysts affording highly heterotactic PLA with Pr = 0.87 and Pr = 0.98, respectively.…”

Aluminum Salen and Salan Polymerization Catalysts: From Monomer Scope to Macrostructure Control

“…Rac-β-BL polymerziation also operated under immortal conditions with catalysts 17 or 43 , even with extremely high amounts of chain transfer agent: [β-BL] 0 :[Al] 0 :[ROH] 0 = 1000:1:50. Our subsequent report on ortho-adamantyl substituted complexes also investigated rac-β-BL polymerization with a particular focus on polymerization kinetics (57). Polymerization of rac-β-BL with phenylene bridged complexes 62 -64 as well as isopentyl bridged complex 61 were not good catalysts for β-BL polymerization (Đ = 1.37 -2.21).…”