Intensive Cycloalkyl-Fused Pyridines for Aminopyridyl-Zinc-Heteroimidazoles Achieving High Efficiency toward the Ring-Opening Polymerization of Lactides.

The model precatalyst sp 3 - and sp 2 -N dinitrogen-coordinated zinc-heteroimidazole has been used as an efficient catalyst for the ring-opening polymerization of cyclic esters. Subsequent to our exceptional active 5,6,7-trihydroquinolin-8-amine-zinc catalysts for the ring-opening polymerization (ROP) of ε -caprolactone, various pyridine-fused cycloalkanones (ring size from five to eight) are developed for the correspondent fused amine-pyridine derivatives and their zinc-heteroimidazole chloride complexes Zn1 - Zn8 ( L ZnCl 2 ) bearing N -diphenylphosphinoethyl pendants. Activated with two equivalents of LiN(SiMe 3 ) 2 , the title zinc complexes efficiently promote the ROP of L -lactide ( L -LA) in situ; among them, Zn4 /2Li(NSiMe 3 ) 2 catalyzed 500 equivalent L -LA at 80 °C with 92% conversion in 5 min (TOF: 5520 h -1 ). Under the same conditions, the catalytic efficiency for the ROP of rac -LA by Zn1 - Zn8 /2Li(NSiMe 3 ) 2 was slightly lower than that for L -LA (highest TOF: 4440 h -1 ). In both cases, cyclooctyl-fused pyridyl-zinc complexes exhibited higher activity than others, while the cycloheptyl-fused zinc complexes showed the lowest activity. The microstructure analysis of the polymers showed they possessed a linear structure capped with CH 3 O as major and cyclic structure as minor. In this work, all the ligands and zinc complexes were well characterized by 1 H/ 13 C/ 31 P NMR, FT-IR spectroscopy as well as elemental analysis.