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 ring-opening polymerization (ROP) among tested initiators
in terms of activity.