Lithium Quinolyl-Amidinates Efficiently Promoting Ring-Opening Polymerization of [epsi]-Caprolactone: Synthesis and 7Li NMR Spectroscopic Studies

Lithium complexes (Li1-Li5) of tridentate quinolyl-amidinate scaffolds were successfully synthesized in high yields and characterized by 1H NMR spectroscopy and multinuclear solution 7Li NMR spectroscopy. The molecular structures of representative complexes Li2 and Li3 were established by single-crystal X-ray diffraction analysis, indicating two four-coordinate lithium atoms connected through two amidinate units. Interestingly, one Li atom is coordinated exclusively by the four N atoms of the quinolyl-amidinate moieties, whereas the other Li atom is coordinated by the amino N atoms of the aminoquinolyl moieties, as well as the N atoms of the aniline moieties. These complexes were found to be highly active towards the ring-opening polymerization of [epsi]-caprolactone, in both the absence and presence of benzyl alcohol as a co-initiator. The mechanistic studies associated with these polymerizations were performed by 1H NMR spectroscopy and 7Li NMR spectroscopy.