Diverse Coordinative Zinc Complexes Containing Amido-Pyridinate Ligands: Structural and Catalytic Studies

In this work, zinc complexes containing amidopyridinate ligands substituted with different pendant arms have been described. Treatment of ligand precursors with ZnEt₂ at a 1:1 ratio in THF yields zinc ethyl complexes (PyN $$ )₂(ZnEt)₂ (1) and (PyN $$ )₂(ZnEt)₂ (2), respectively. Complexes 1 and 2 show the same geometry as a distorted tetrahedron, but adopt different coordination behaviors supported by the ligands. Complex 1 represents a rare and a non-centrosymmetric mode, which the amido group bridges two zinc centers to form a six-membered ring. However, complex 2 shows a centrosymmetric mode, which the pyridine group links to the zinc centers to form an eight-membered ring. Recrystallization of complex 2 gives an additional complex (PyN $$ )₄Zn₃(μ³-O) (3). We attempted to prepare zinc benzyl oxide complexes but afforded only a self-assembly cubane complex Zn₇Et₆(OBn)₈ (4). All molecular structures 1-4 are characterized depending on both single-crystal X-ray and spectroscopic data. Furthermore, their catalytic properties toward the ring opening polymerization of ε-caprolactone and L-lactide, using benzyl alcohol as the initiation reagent, are under investigation.