N-Benzoylbenzamidinate complexes of aluminium: highly efficient initiators for the ring-opening polymerization of ε-caprolactone

Abstract

A series of aluminium complexes supported by amidinate-based N,O-chelate ligands are synthesized and characterized. While complexes [L^DippAlMe₂] (1) and [L^PhAlMe₂] (2) are prepared by treating N-benzoyl-N′-2,6-diisopropylphenylbenzamidine (L^DippH) and N-benzoyl-N′-phenylbenzamidine (L^PhH) with a slight excess of 1 equiv. of AlMe₃, complexes [(L^Dipp)₂AlMe] (3) and [(L^Ph)₃Al] (4) can be obtained using the ligands and AlMe₃ in 2 : 1 and 3 : 1 molar ratios respectively. Complexes 1–4 have been characterized by ¹H/¹³C NMR spectroscopy and elemental analysis. The molecular structures of complexes 1, 3 and 4 have also been determined by single crystal X-ray diffraction technique. 1, 2 and 3 are highly active initiators for the ring opening polymerization (ROP) of ε-caprolactone and produce polycaprolactone with very high molecular weight and narrow molecular weight distribution. These complexes are also active toward the ROP of cyclohexene oxide.