Cationic indium catalysts for ring opening polymerization: tuning reactivity with hemilabile ligands.

This is a comprehensive study of the effects of rationally designed hemilabile ligands on the stability, reactivity, and change in catalytic behavior of indium complexes. We report cationic alkyl indium complexes supported by a family of hemi-salen type ligands bearing hemilabile thiophenyl (), furfuryl () and pyridyl () pendant donor arms. Shelf-life and stability of these complexes followed the trend < < , showing direct correlation to the affinity of the pendant donor group to the indium center. Reactivity towards polymerization of epichlorohydrin and cyclohexene oxide followed the trend > > with control of polymerization following an inverse relationship to reactivity. Surprisingly, polymerized lactide without an external initiator, likely through an alkyl-initiated coordination-insertion mechanism.