Mechanistic comparison of cyclic ester polymerizations by novel iron(III)-alkoxide complexes: Single vs multiple site catalysis

被引：281

作者：

O'Keefe, BJ ^{[1
]}

Breyfogle, LE ^{[1
]}

Hillmyer, MA ^{[1
]}

Tolman, WB ^{[1
]}

机构：

[1] Univ Minnesota, Dept Chem, Minneapolis, MN 55455 USA

来源：

JOURNAL OF THE AMERICAN CHEMICAL SOCIETY | 2002年 / 124卷 / 16期

关键词：

D O I：

10.1021/ja012689t

中图分类号：

O6 [化学];

学科分类号：

0703 ;

摘要：

The complexes Fe-2(OCHPh2)(6) and L2FeOR (R = Et or CHPh2, L = N,N'-bis(trimethylsilyl)-benzamidinate) were structurally characterized, and comparative studies of the behavior of those compounds comprising the same alkoxide (Ph2HCO-) in polymerizations of epsilon-caprolactone (CL) and D,L-lactide (LA) were performed. Both Fe-2(OCHPh2)(6) and L2FeOCHPh2 are effective polymerization catalysts, as reflected by molecular weight control, polydispersities, and end group analysis, but the diiron complex generally exhibits greater polymerization control, particularly for CL. Kinetic investigations of the polymerization of CL revealed the same first-order dependence on [CL] for both catalysts, but different orders in [catalyst] that signified a distinct contrast in mechanism. Analysis that invoked the presence of a termination-causing impurity at low concentration yielded a first-order dependence on [Fe-2(OCHPh2)(6)], but the order in [L2FeOCHPh2] was found to be one-half, This fractional dependence was interpreted by using a model of active chain aggregation. Comparison of the derived propagation rate constants (k(prop)) revealed a similar to50-fold greater value for the diiron complex compared to the single site mononuclear compound. Implications of these findings for understanding cyclic ester polymerization mechanisms and catalyst design are discussed.

引用

页码：4384 / 4393

页数：10

共 56 条

[41] Molecular structure of the methoxy-iron(III) derivative of 5,15-(o,o′(2-methyl-2′-hydroxy-3,3′-diamidobiphenyl)-diphenyl)-porphyrin and CO binding properties of iron(II)-pyridine complexes of 2,2′-substituted biphenyl strapped porphyrins [J].