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Abstract
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.
Highlights
The role of polyesters has been given much attention due to their essential characteristics of being biodegradable, biocompatible, and permeable (Puelacher et al, 1994; Cheng et al, 1999)
Benzyl alcohol was dried over magnesium sulfate and distilled before use. ε-Caprolactone was dried over magnesium sulfate and L-Lactide was recrystallized from toluene prior to use
The ligand precursors, HNPyCEn are more synthesized by copper catalysis under air-controlled conditions than with other preparations (Foxon et al, 2002; Liu et al, 2007)
Summary
The role of polyesters has been given much attention due to their essential characteristics of being biodegradable, biocompatible, and permeable (Puelacher et al, 1994; Cheng et al, 1999). Various kinds of metal complexes, such as Al, Mg, Zn, Fe, and Sn, have been well-studied as initiators/catalysts and control very well the molecular properties of the polymers (O’keefe et al, 2001; Coates, 2002; Nakano et al, 2003; Chisholm and Zhou, 2004; Coates and Moore, 2004; Wu et al, 2006; Wheaton et al, 2009). Low-toxic and environmentally friendly metal centers such as magnesium, calcium, and zinc are fascinating candidates with a crucial role in aiding to synthesize compounds with ancillary ligands (Wheaton et al, 2009). Employing a steric bulky ligand or pendant arm(s) coordinated to an active metal center provides a barrier to hinder these undesired polymers. As a result of the successful application of β-diketiminate (BDI) complexes in ring opening polymerization, alternative or
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