Aluminum chelates supported by β-quinolyl enolate ligands: synthesis and ROP of ε-CL

Treatment of tautomers of β-quinolyl ketone-enaminones with AlMe3 afforded β-quinolyl enolato dialkylaluminium complexes LAlMe2 (L = [(2-C9H6N)-CH[double bond, length as m-dash]C(R)-O-], R = CH3 (), (t)Bu (), Ph (), o-tolyl (), p-tolyl (), p-OMePh ()), respectively. reacted with benzyl alcohol to generate the corresponding LAl(OBn)2 complex . Complexes and were characterized by (1)H and (13)C NMR spectroscopy, elemental analyses and single crystal X-ray diffraction analyses. All complexes were tested as catalyst precursors for ring-opening polymerization of ε-caprolactone (ε-CL). The results indicated that LAlMe2 () exhibited good activity towards the ROP of ε-CL in the presence of benzyl alcohol at 80 °C, and LAl(OBn)2 exhibited higher catalytic activity in the absence of alcohol than for the ROP of ε-CL. However, both polymerizations were less controlled. Kinetic studies showed that the polymerization reaction catalyzed by and proceeded with first-order dependence on the monomer and took place through coordination-insertion.