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.

Automated summary

The synthesis of heteroleptic and homoleptic complexes was achieved by designing the ligands. Heteroleptic ethyl zinc complexes 1a-3a were obtained by eliminating ethane. However, only homoleptic complexes 3b and 4b could be isolated from the reaction of proligands 3 and 4 with Zn[N(SiMe3)2]2 at room temperature. Surprisingly, proligand 2 cleanly produced the amide heteroleptic zinc complex 2c in the reaction with Zn[N(SiMe3)2]2, and 2c showed the most promising activity in ring-opening polymerization (ROP) among the tested initiators.