Department of Chemistry
home :: people :: faculty
Print    Email

Megan Fieser

Gabilan Assistant Professor of Chemistry
Inorganic Chemistry

B.A. 2010, Washington University in St. Louis
Ph.D. 2015, University of California, Irvine
Office: SGM 218
Phone: 213-821-4228
Fax: (213) 740-6679
 Group Homepage

Research Focus


Although Lewis acid catalysts are known to have high reactivities for some reactions, their chemistry has not been as well developed as that of precious metal catalysts. Most Lewis acid catalysts simply function to bind a substrate in the proximity of an activating group that does nucleophilic attack. It is our aim however, to show how careful catalyst design and mechanistic studies can be used to expand the potential of these catalysts to affect a wider range of transformations. Specifically, Lewis acidic metal complexes have been shown as promising catalysts for polymerization and depolymerization reactions. Since the growing demand and accumulation of plastics remains a challenge for chemistry, our focus will be on catalyst development for the synthesis of degradable polymers that could be used as replacements for petroleum-based plastics as well as the degradation of current polymers.

Perfectly Alternating Copolymerization of Epoxides and Cyclic Anhydrides

The alternating copolymerization of epoxides and cyclic anhydrides is an alluring route to polyesters with a wide range of different properties. However, current catalyst design has not led to industrially relevant polymerization rates or conditions. Rare-earth catalysts are ideal candidates for the target copolymerization since they have been useful for the ring opening polymerization of other polar monomers such as ε-caprolactone, lactide and methyl methacrylate. The primary goal of this work is to identify rare-earth catalysts that can rapidly produce polyester plastics from the copolymerization of epoxides and cyclic anhydrides at industrially relevant conditions.

Metal Catalyst Design for the Controlled Degradation of PET and PEF

Poly(ethylene terephthalate) (PET) is a useful plastic, industrially produced on the millions of tons scale, while poly(ethylene furanoate) (PEF) is an emerging 100% bio-based replacement for PET. This work strives to use environmentally friendly Lewis acidic metal alkoxide complexes for the catalytic chemical degradation of PET and PEF as a more facile route than current solvolysis routes. Two strategies for ligand choices will be used in designing these catalysts. One strategy will use steric crowding to break polymers down into individual building blocks (shown in blue). The other strategy will use sterically unsaturated metal complexes to target intramolecular transesterification, or back-biting, to allow the formation of low molecular weight macrocycles (shown in red). Both routes would lead to sustainable recycling methods for plastics currently produced at industrial scale.

Mechanistic Studies of Sequential Catalysts

Metal catalysts that can mediate multiple transformations in a selective manner is an expanding area of catalysis. A mechanistic understanding of these transformations would help lead future catalyst design efforts. The aim of this work is to study cationic rare-earth metal catalysts that are able to polymerize nonpolar olefins followed by polar ε-caprolactone at room temperature, to form block copolymers with reasonable rates and good molecular weight control. These block copolymers of olefins and polar monomers are a promising class of plastics that are capable of showing remarkable adhesive, dyeing and moisture absorption properties. We will strive to modify the current catalysts and/or design new catalysts to improve polymerization control and selectivity, as well as increase catalyst 

Selected publications


19) Fieser, M. E.;* Sanford, M. J.;* Mitchell, L. A.; Dunbar, C. R.; Mandal, M.; Van Zee, N. J.; Urness, D. M.; Cramer, C. J.; Coates, G. W.; Tolman, W. B. “Mechanism of Copolymerization of Epoxides with Cyclic Anhydrides, Using Aluminum and Iminium Salt Cocatalysts” J. Am. Chem. Soc. 2017,139, 15222-15231. *Authors contributed equally to this work.

18) Palumbo, C. T.; Fieser, M. E.; Ziller, J. W.; Evans, W. J. “Reactivity of Complexes of 4fn5d1 and 4fn+1 Ln2+ Ions with Cyclooctatetraene” Organometallics 2017, 36, 3721-3728.

17) Fieser, M. E.; Palumbo, C. T.; La Pierre, H. S.; Halter, D. P.; Voora, V. K.; Ziller, J. W.; Furche, F.; Meyer, K.; Evans, W. J. “Comparisons of Lanthanide / Actinide +2 Ions in a Tris(aryloxide)arene Coordination Environment” Chem. Sci. 2017, 8, 7424-7433.

16) Fieser, M. E.;* Ferrier, M. G.;* Su, J.;* Batista, E.; Evans, W. J.; Lezama, J. S.; Kozimor, S. A.; Olson, A. C.; Wagner, G. L.; Vitova, T.; Yang, P. “Evaluating the Electronic Structure of Formal LnII Ions in LnII(C5H4SiMe3)31– Complexes Using XANES Spectroscopy and DFT Calculations” Chem. Sci. 2017, 8, 6076–6091. *Authors contributed equally to this work.

15) Fieser, M. E.; Woen, D. H.; Corbey, J. F.; Mueller, T. M.; Ziller, J. W.; Evans, W. J. “Raman Spectroscopy of the N–N Bond in Rare Earth Dinitrogen Complexes” Dalton Trans. 2016, 45, 14634–14644. Part of Themed Collections: Celebrating the 2017 RSC Prize and Award Winners and Small Molecule Activation.

14) Langeslay, R. R.; Fieser, M. E.; Ziller, J. W.; Furche, F.; Evans, W. J. “Expanding Thorium Hydride Chemistry Through Th2+ Including the Synthesis of a Mixed-Valent Th4+/Th3+ Hydride Complex” J. Am. Chem. Soc. 2016, 138, 4036–4045.

13) Kotyk, C. M.; Fieser, M. E.; Palumbo, C. T.; Ziller, J. W.; Darago, L. E.; Long, J. R.; Furche, F.; Evans, W. J. “Isolation of +2 rare earth metal ions with three anionic carbocyclic rings: bimetallic bis(cyclopentadienyl) reduced arene complexes of La2+ and Ce2+ are four electron reductants” Chem. Sci. 2015, 6, 7267–7273.

12) Fieser, M. E.; Johnson, C. W.; Bates, J. E.; Ziller, J. W.; Furche, F.; Evans, W. J. “Dinitrogen Reduction, Sulfur Reduction and Isoprene Polymerization via Photochemical Activation of Trivalent Bis(cyclopentadienyl) Rare-Earth-Metal Allyl Complexes” Organometallics 2015, 34, 4387–4393.

11) Meihaus, K. R.; Fieser, M. E.; Corbey, J. F.; Evans, W. J.; Long, J. R. “Record High Single-Ion Magnetic Moments through 4fn5d1 Electronic Configurations in the Divalent Lanthanide Complexes [(C5H4SiMe3)3Ln]1–J. Am. Chem. Soc. 2015, 137, 9855–9860.

10) Corbey, J. F.; Woen, D. H.; Palumbo, C. T.; Fieser, M. E.; Ziller, J. W.; Furche, F.; Evans, W. J. “Ligand Effects in the Synthesis of Ln2+ Complexes by Reduction of Tris(cyclopentadienyl) Precursors Including C-H Bond Activation of an Indenyl Ligand” Organometallics 2015, 34, 3909–3921.

9) Fieser, M. E.; MacDonald, M. R.; Krull, B. T.; Bates, J. E.; Ziller, J. W.; Furche, F.; Evans, W. J. “Structural, Spectroscopic, and Theoretical Comparison of Traditional vs Recently Discovered Ln2+ Ions in the [K(2.2.2-cryptand)][(C5H4SiMe3)3Ln] Complexes: The Variable Nature of Dy2+ and Nd2+J. Am. Chem. Soc. 2015, 137, 369–382.

8) Langeslay, R. R.; Fieser, M. E.; Ziller, J. W.; Furche, F.; Evans, J. W. “Synthesis, Structure, and Reactivity of Crystalline Molecular Complexes of the {[C5H3(SiMe3)2]3Th}1– Anion Containing Thorium in the Formal +2 Oxidation State” Chem. Sci. 2015, 6, 517–521.

7) Fieser, M. E.; Mueller, T. J.; Ziller, J. W.; Evans, W. J. “Differentiating Chemically Similar Lewis Acid Sites in Heterobimetallic Complexes: The Rare-Earth Bridged Hydride (C5Me5)2Ln(μ-H)2Ln’(C5Me5)2 and Tuckover Hydride (C5Me5)2Ln(μ-H)(μ-k1:η5-CH2C5Me4)Ln’(C5Me5) Systems” Organometallics 2014, 33, 3882–3890.

6) MacDonald, M. R.; Fieser, M. E.; Bates, J. E.; Ziller, J. W.; Furche, F.; Evans, W. J. “Identification of the +2 Oxidation State for Uranium in a Crystalline Molecular Complex, [K(2.2.2-Cryptand)][(C5H4SiMe3)3U]” J. Am. Chem. Soc. 2013, 135, 13310–13313.

5) Kindra, D. R.; Casely, I. J.; Fieser, M. E.; Ziller, J. W.; Furche, F.; Evans, W. J. “Insertion of CO and COS into Bi–C Bonds: Reactivity of a Bismuth NCN Pincer Complex of an Oxyarl Dianionic Ligand, [2,6-(Me2NCH2)2C6H3]Bi(C6H2tBu2O)” J. Am. Chem. Soc. 2013, 135, 7777–7787.

4) Fieser, M. E.; Bates, J. E.; Ziller, J. W.; Furche, F.; Evans, W. J. “Dinitrogen Reduction via Photoactivation of Heteroleptic Tris(cyclopentadienyl) Rare-Earth Complexes” J. Am. Chem. Soc. 2013, 135, 3804–3807.

3) Schmiege, B. M.; Fieser, M. E.; Ziller, J. W.; Evans, W. J. “Reactivity of the Y3+ Tuck-over Hydride Complex, (C5Me5)2Y(μ-H)(μ-CH2C5Me4)Y(C5Me5)” Organometallics 2012, 31, 5591–5598.

2) MacDonald, M. R.; Bates, J. E.; Fieser, M. E.; Ziller, J. W.; Furche, F.; Evans, W. J. “ Expanding Rare- Earth Oxidation State Chemistry to Molecular Complexes of Holmium(II) and Erbium(II)” J. Am. Chem. Soc. 2012, 134, 8420–8423.

1) Mueller, T. J.; Fieser, M. E.; Ziller, J. W.; Evans, W. J. “(C5Me4H)1–- Based Reduction of Dinitrogen by the Mixed Ligand Tris(polyalkylcyclopentadienyl) Lutetium and Yttrium Complexes, (C5Me5)3-x(C5Me4H)xLn” Chem. Sci. 2011, 2, 1992–1996. 

© 2020 Department of Chemistry , USC