Toward the Synthesis of Heteroleptic Zinc ROP Initiators Based on Pyridine-Containing Monoalcohols by Tuning Ligand Substituents

Synthesis of two types of complexes (heteroleptic vs homoleptic) is accomplished by an elegant variation of the ligand design. Heteroleptic ethyl zinc complexes 1a-3a were cleanly obtained via ethane elimination. Nevertheless, in the reaction of proligands 3 and 4 with Zn[N(SiMe3)2]2 performed at room temperature, only homoleptic complexes 3b and 4b can be isolated. Surprisingly, proligand 2 was found to cleanly produce amide heteroleptic zinc complex 2c in the reaction with Zn[N(SiMe3)2]2, and 2c seems to be the most promising in ringopening polymerization (ROP) among tested initiators in terms of activity.