Transcript honors_presentation_120916x

Iron Organometallics toward Olefin Metathesis and
an Atomically-Precise Iron Oxide Nanocluster
Jonathan A. Kephart, Gaurab Rimal, Navamoney Arulsamy, Jinke Tang, Elliott B. Hulley*
University of Wyoming, Senior Honors Project, December 9, 2016
First Story: Organometallics
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The properties of isolated metal atoms can be tuned through the
coordination of an organic ligand framework.
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Systematic modification of the ligand framework can establish
catalytic activity for manipulation of organic substrates.
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Organic – Compounds composed mostly of C, O, N, and H
Olefin Metathesis
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Olefin Metathesis– Metal catalyzed scrambling of carboncarbon double bonds (olefins)
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Alkylidene – Metal-carbon double bond
General Mechanism
Polymer Synthesis
Pharmaceutical Synthesis
2005 Nobel Prize in Chemistry
Yves Chauvin
Robert Grubbs
Richard Schrock
“for the development of the metathesis method in organic chemistry”
Metathesis Catalysts
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First-row Counterparts
Benchmark Catalysts
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Carbonyl ligands retract electron density
from metal center
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Iron-based alkylidenes only active to
cyclopropanation
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PROs: Excellent activity and/or selectivity
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CONs: Based on toxic or expensive heavy metals
Metathesis and the Hulley Group
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Use a bifunctional ligand platform with a pendent binding group
(Nu) to stabilize the alkylidene.
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Cyclopentadiene (Cp) and phosphine will provide a stable,
electron-rich iron center.
stable
Nu
L
CH2
FeII
Nu = Nucleophile
reactive
Nu
CH2
L
FeIV
Olefin Metathesis,
Cyclopropanation
Furstner et al., J. Am. Chem. Soc. 2008, 130 (6), 1992-2004
Initial Synthetic Approach
Iron-Lithium Bimetallic Complexes
Proposed
Hydride
Signal
Subsequent Synthetic Work

Alkyl and Di-alkyl Iron Precursors
Fe(Np)2(TMEDA)
Fe(Np)Cl(TMEDA)
Fe(Nph)Cl(TMEDA)
Half-sandwich and Target Synthesis

Di-alkyl complexes are used to generate half-sandwich compounds.
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With a half-sandwich iron alkyl complex in hand, the target catalyst
is one step away.
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BULK vs. NANO: The properties of nano-scale and bulk materials are
very different.
Bulk Gold:
 Gold Nanoparticles:
Surface Plasmon Resonance

Let’s take the nano-scale one step further…
Sun et al., J. Am. Chem. Soc. 2013, 135, 16833-16836.
A. Maeland and T. B. Flanagan, Can. J. Phys., 1964, 42, 2364.
Second Story: Iron Oxide Nanocluster
Magic-Number Clusters – Small nanoparticles (<5 nm) that are stable with a specific
number of atoms… atomically-precise and monodisperse… a magic number.
(left) Au25(SR)18
(right) Au25(PR3)10(SR)5Cl2
Buckminsterfullerene – C60
[Au23(PhC2)9(Ph3P)6]2+
Jin, R. Nanotechnol Rev 1 2012, 31-56.
Wan et al. Angew. Chem. Int. Ed. 2015, 54, 5977-5980.
Magic Number Clusters
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Using mass spectrometry, Sun et al. predicted the existence of Fe9O6 and Fe13O8.
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They performed quantum chemical calculations to optimize core geometries.
Mass Spectra
Fe9O6
Fe13O8
Sun et al. Physical Review B 1999, 61, 5781-5785.
Sun et al. Physical Review B 2000, 62, 8500-8507.
Magic Number Iron Oxide
Synthesis of Fe9O6(Np)6(TMEDA)3
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Cluster was inadvertently synthesized and characterized via XRD while
working with Fe(Np)2(TMEDA).
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(Whoops!)
Fe9O6Np6(TMEDA)3
Crystalline State
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Rhombohedral
Crystal Packing
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Asymmetric Unit:
Fe2O(Np)(TMEDA)1/2
Cores and Voids
Solution-phase Magnetic Behavior
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VT-NMR experiments were performed to probe the short-range
temperature dependence of magnetic properties.
Solvent D8-toluene
Capillary D8-toluene
µeff,ave = 7.3 B.M.
Solid-state Magnetic Behavior
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Solid-state magnetic analysis performed in collaboration w/ the Tang Group.
Fresh/Crystalline Sample
Old/Powder Sample
spin glass behavior
paramagnetic behavior
Spin Glass
Ferromagnet
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Perform computational analysis of vibrations and electronic states
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Assess utility as solid-state synthetic precursor or catalyst
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Fully characterize magnetic/spectroscopic behavior
Yang et al. Nat Communications 2013, 4, 2422.
Roy, X. J. Am. Chem. Soc. 2014, 136, 16926−16931.
Fe9O6 Future Work
Thank You for Your Time!
Wild, Wonderful, Windy Wyoming