Redox Control of Aluminum Ring-Opening Polymerization: A Combined Experimental and DFT Investigation

The synthesis, characterization,
and reactivity of an aluminum
alkoxide complex supported by a ferrocene-based ligand, (thiolfan*)­Al­(OtBu) (1red, thiolfan* = 1,1′-di­(2,4-di-tert-butyl-6-thiophenoxy)­ferrocene),
are reported. The homopolymers of l-lactide (LA), ε-caprolactone
(CL), δ-valerolactone (VL), cyclohexene oxide (CHO), trimethylene
carbonate (TMC), and their copolymers were obtained in a controlled
manner by using redox reagents. Detailed DFT calculations and experimental
studies were performed to investigate the mechanism. Mechanistic studies
show that, after the insertion of the first monomer, the coordination
effect of the carbonyl group, which has usually been ignored in previous
reports, can significantly change the energy barrier of the propagation
steps, thus playing an important role in polymerization and copolymerization
processes.