Synthesis and characterisation of aluminium(iii) and tin(ii) complexes bearing quinoline-based N,N,O-tridentate ligands and their catalysis in the ring-opening polymerisation of ε-caprolactone

Abstract

The synthesis and catalysis in the ring-opening polymerisation (ROP) of ε-caprolactone (ε-CL) of aluminium(III) and tin(II) complexes supported by quinoline-based N,N,O-tridentate ligands are reported. Reaction of 8-{RC(O)CH₂P(Ph₂)N}C₉H₆N (R = Bu^t, 2; R = Ph, 3) with AlMe₃ gave [Al(Me₂){OCRCHP(Ph₂)N(8-C₉H₆N)}] (R = Bu^t, 4; R = Ph, 5). Treatment of 2 and 3 with Sn[N(SiMe₃)₂]₂ generated tin(II) complexes [Sn{OC(R)CHP(Ph₂)N(8-C₉H₆N)}{N(SiMe₃)₂}] (R = Bu^t, 6; R = Ph, 7). A similar reaction of AlMe₃ with 8-{MeC(O)CH₂C(Me)N}C₉H₆N gave [Al(Me₂){OC(Me)CHC(Me)NC₉H₆N}] (9). Compounds 2–9 were characterised by NMR spectroscopy and elemental analysis. The molecular structures of complexes 4, 6 and 9 were determined by single crystal X-ray diffraction techniques. Investigation of catalysis of complexes 4–7 and 9 in the ROP of ε-CL revealed that the aluminium complexes, 4, 5 and 9, are much more active than the tin(II) complexes. The kinetic studies for the polymerisation of ε-CL catalysed by complexes 4, 5 and 9 in the presence of benzyl alcohol (BnOH) indicated that the polymerisations proceed with the first-order dependence on monomer concentration. The polymerisation was well controlled and gave a polymer with narrow molecular weight distribution.