Zirconium Complexes Containing [NOON]‐Type Ligands for Isoselective Polymerization of <i>rac</i> ‐Lactide

ABSTRACT Several racemic zirconium complexes 1–8 featuring [NOON]‐type ligands were synthesized through alkane elimination reactions between Zr(CH 2 SiMe 3 ) 4 and the respective new proligands in toluene. Spectral and elemental analyses were used to characterize these complexes, which demonstrated good performance in rac ‐lactide polymerization. All complexes displayed comparable catalytic activity, with 5 exhibiting the highest activity (TOF = 58.7 h −1 ) and 8 yielding polylactide with the highest molecular weight ( M n = 8.6 × 10 4 g/mol). Notably, these systems outperform existing zirconium complexes bearing [NSSN]‐type, [OSSO]‐type, and ethylene‐bridged [ONSO]‐type ligands, as well as phosphasalen Ti/Zr complexes, under analogous polymerization conditions. To enhance the stereoselectivity of these systems, four co‐agents—pyridine, 2,2′‐bipyridine, DME, and TMEDA—were evaluated. TMEDA was found to significantly improve the stereocontrol of all complexes, with complex 2 showing the highest stereoregularity ( P m = 0.72).