Mechanistic Comparison of Cyclic Ester Polymerizations by Novel Iron(III)−Alkoxide Complexes: Single vs Multiple Site Catalysis
- 23 March 2002
- journal article
- research article
- Published by American Chemical Society (ACS) in Journal of the American Chemical Society
- Vol. 124 (16), 4384-4393
- https://doi.org/10.1021/ja012689t
Abstract
The complexes Fe2(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 ε-caprolactone (CL) and d,l-lactide (LA) were performed. Both Fe2(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 [Fe2(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 (kprop) revealed a ∼50-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.Keywords
This publication has 17 references indexed in Scilit:
- Polymerization of Lactide by Monomeric Sn(II) Alkoxide ComplexesMacromolecules, 2002
- 203,205Tl NMR Studies of Crystallographically Characterized Thallium Alkoxides. X-ray Structures of [Tl(OCH2CMe3)]4 and [Tl(OAr)]∞, Where OAr = OC6H3(Me)2-2,6 and OC6H3(CHMe2)2-2,6Inorganic Chemistry, 2001
- Polymerization of Lactide with Zinc and Magnesium β-Diiminate Complexes: Stereocontrol and MechanismJournal of the American Chemical Society, 2001
- Coordination polymerization of heterocyclic and heterounsaturated monomersProgress in Polymer Science, 1998
- Polymerization of l,l-Lactide Initiated by Aluminum Isopropoxide Trimer or TetramerMacromolecules, 1998
- Ring-Opening Polymerization of d,l-Lactide Using Rare-Earth μ-Oxo Isopropoxides as Initiator SystemsMacromolecules, 1997
- Recent Advances in Ring-Opening Polymerization of Lactones and Related CompoundsJournal of Macromolecular Science, Part C: Polymer Reviews, 1995
- Completion and refinement of crystal structures withSIR92Journal of Applied Crystallography, 1993
- A novel and generalized approach to the synthesis of ML3n+ [M = ruthenium(II), rhodium(III); L = 2,2'-bipyridine, 1,10-phenanthroline, 2-(arylazo)pyridine; n = 2, 3]Inorganic Chemistry, 1992
- Utilizing the Evans method with a superconducting NMR spectrometer in the undergraduate laboratoryJournal of Chemical Education, 1992