Zinc Complexes Supported by Maltolato Ligands: Synthesis, Structure, Solution Behavior, and Application in Ring-Opening Polymerization of Lactides
作者:Rafał Petrus、Piotr Sobota
DOI:10.1021/om300321h
日期:2012.7.9
A series of novel zinc alkoxides supported by chelating maltolato (MalO; MalOH = maltol) ligands were successfully synthesized and characterized. Reaction of MalOH with ZnEt2 (3:4) gives a trinuclear cluster [Zn-3(Et)(2)(MalO)(4)] (1), which spontaneously disproportionates in solution to mononuclear species [Zn(MalO)(2)] (1a) and [Zn(Et)(MalO)] (1b); (1a) and (1b) form [Zn(MalO)(2)(py)] (2), [Zn(Et)(MalO)(py)] (3), [Zn(MalO)(2)](2) ((1a)(2)), [Zn(MalO)(OBn)](2) ((1c)(2)), and [Zn-4(Et)(2)(OEt)(2)(MalO)(4)] (4) on addition of pyridine, benzyl alcohol (BnOH), or dry O-2, respectively. Compounds 1, 2, (1a)(2), and 4 were characterized by elemental analysis, NMR. ESI-MS, and single-crystal X-ray structural analysis. Variable-temperature NMR experiments showed that (1a)(2) and (1c)(2) are in equilibrium with the monomeric form in solution. The addition of L-Iactide (L-LA) to a combination of 1 and 2 equiv of BnOH in dichloromethane at room temperature in different molar ratios leads to rapid and efficient generation of poly(L-LA) with end-capped BnO groups. According to kinetic studies, propagation by [Zn(OBn)(MalO)] (1c) is first-order with respect to both the monomer and 1c concentrations; 1a in ring-opening polymerization of L-LA shows no activity. These results suggest a single-site active species in the ring-opening polymerization of L-LA.
Annan, Theodore A.; Peppe, Clovis; Tuck, Dennis G., Canadian Journal of Chemistry, 1990, vol. 68, # 9, p. 1598 - 1605
作者:Annan, Theodore A.、Peppe, Clovis、Tuck, Dennis G.