Aluminium complexes containing N,N′-chelating amino-amide hybrid ligands applicable for preparation of biodegradable polymers

Abstract

Five aluminium complexes containing N,N'-chelating ligands ([2-(Me2NCH2)C6H4N(R)]−; R = H, SiMe3 or benzyl (Bn)) were prepared and structurally characterized by NMR and crystallographic techniques. Aluminium atoms in all compounds are pseudotetrahedrally coordinated with extremely short intramolecular interaction of the pendant amino group (d(Al–N) = 1.96–2.00 Å). The catalytic performance of selected complexes (∼0.1–0.2 mol. %), either with or without an external co-initiator, in ring opening (co)polymerization of ε-caprolactone, l-lactide and trimethylene carbonate was tested yielding satisfactory to excellent amount of polymeric material with Mn ∼ 15–70 kg/mol for ε-caprolactone, and ∼30 kg/mol for trimethylene carbonate with good degree of control over the molar mass distribution, initiation efficiency. An excellent conversion of l-lactide to methyl (S,S)-O-lactyllactate is observed upon catalysis by one of the complexes at room temperature.