Fast and living ring-opening polymerization of ε‑caprolactone by aluminum complexes bearing amino-quinoline ligands

Catalysts drive innovation in sustainable polymers because of their reactivity and selectivity. In this context, the synthesis and characterization of a series of Al complexes ( Al1  −  Al5 ) bearing N,N-bidentate amino-quinoline ligands are described, as well as their applications in ring-opening polymerization (ROP) of ε -caprolactone ( ε -CL). The amido-coordination Al complexes were directly synthesized by reactions of imino-quinoline compounds with AlMe 3 via methyl migration from Al to the carbon atom of imine, as indicated by both NMR spectroscopy and X-ray diffraction. In the presence of BnOH, complexes Al1  −  Al5 showed significant reactivity for ROP of ε -CL with good control over molar mass ( M n ) and dispersity ( Đ < 1.2), and polycaprolactones (PCLs) with high molecular weights ( M n up to 129 kDa) were readily synthesized. Remarkably, immortal catalysis with excess of BnOH (up to 20 equiv. to Al) was achieved to prepare PCLs with predictable M n s, low dispersities, and end groups using an extremely low loading of Al complex (0.05 mol% to ε -CL monomer).