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

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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 = But, 2; R = Ph, 3) with AlMe3 gave [Al(Me2){OCRCHP(Ph2)N(8-C9H6N)}] (R = But, 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 = But, 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.

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