| |
Research Overview
Organometallic Chemistry
Primary interests of the group are the development of new stereospecific
catalysts for organic transformations and polymerizations, and
the investigation of organometallic structure and mechanism. The
projects are largely synthetic in nature, requiring the use of
air and moisture sensitive compounds. These are routinely handled
on a Schlenk or high vacuum line or in an inert atmosphere glove
box. Characterization relies heavily on multinuclear NMR and X-ray
crystallography. Other important instrumental techniques are electron
spin resonance (EPR), gas chromatography (GC), high pressure liquid
chromatographies (HPLC and GPC), and thermal analysis (DSC and
TGA). Theoretical calculations are also used as important tools
in understanding many of the systems under study.
Asymmetric Catalysts
In recent years, there has been considerable effort directed toward
the use of chiral metal complexes as catalysts for a wide variety
of asymmetric transformations. For example, it is often possible
to transform an achiral substrate into a chiral product consisting
almost entirely of one enantiomer. This type of transformation
is extremely important for the synthesis of drugs and natural products,
which usually contain at least one chiral center.
One focus of the group is the development of new transition-metal
catalysts for stereoselective transformations, with a particularly
emphasis on traditionally difficult reactions, such as the hydrogenation
of highly substituted olefins. Both early and late metal systems
are under study. Early metal systems include group 3 and 4 metallocene
complexes and the late metal chemistry will initially focus on
iridium. In either case, the synthesis of new chiral ligands and
metal complexes is a critical aspect of the research. We are also
very interested in why systems behave the way they do. As a result,
mechanistic studies, frequently involving nuclear isotope labeling,
are important in our research. In addition to homogeneous catalysis
with descrete molecules, we are also interested in developing supported
catalysts, and catalysts contained in hosts such as zeolites (see
figure below).
Olefin Polymerization
Olefin polymerization with soluble organometallic catalysts is
a large and growing field. Catalysts can operate at extremely rapid
rates and produce polymers with well-defined microstructures and
predictable bulk properties (see figure below). There is a strong
push to develop catalysts which will produce new types of polymeric
materials for a variety of uses. The group is interested in Group
3 and 4 transition metal catalysts as well as chromium and vanadium
based systems. In some cases there exist heterogeneous catalysts
which are poorly understood, and the study of homogeneous analogs
can provide valuable information about industrial processes.
Organometallic Structure and Mechanism
Fulvenes can be though of as oxidized forms of cyclopentadienyl
(Cp) ligands, and as such are closely related (see figure below).
The fulvene moiety has received relatively little attention as
a ligand compared to Cp's. One project in the group is to examine
the structure and reactivity of transition-metal fulvene complexes,
with particular attention on new ways of synthesizing novel Cp
complexes via fulvene complexes.
Selected Publications
Levy, C. J.; Henling,
L. M.; Day, M. W.; Bercaw, J. E. "The Polymerization of Chiral a-Olefins with an Enantiopure
C1-Symmetric Zirconocene Catalyst" J. Am. Chem. Soc. submitted
for publication.
Bondar, G.V. ; Aldea, R., Levy, C. J.;
Jaquith, J. B.; Collins, S. "Asymmetric Catalysis of the Diels-Alder Reaction Using
Dicationic Zirconocene Complexes" Organometallics, 2000, 65,
947-949.
Lin, S. Q.; Bondar, G. V.; Levy, C. J.;
Collins, S. "Mukaiyama
Aldol Reactions Catalyzed by Zirconocene Bis(triflate) Complexes:
Stereochemistry and Mechanisms for C-C Bond Formation". J.
Org. Chem. 1998, 63, 1885-1892.
Jaquith, J. B.; Levy, C. J.;Bondar, G.
V.; Wang, S. T.; Collins, S. "Diels-Alder Reactions of Oxazolidinone Dienophiles Catalyzed
by Zirconocene Bis(triflate) Complexes: Mechanism for Asymmetric
Induction". Organometallics 1998, 17, 914-925.
Hill, G. S.; Irwin, M. I.; Levy, C. J.;
Rendina, L. M.; Puddephatt, R. J. "Platinum(II) Complexes of Dimethyl Sulfide". Inorganic
Synthesis Volume 32., pp 149-153. Darensbourg, M. Y. Ed. John Wiley & Sons,
Toronto, 1998.
Levy, C. J.; Puddephatt, R. J. "Thermal Decomposition of
Platinum(IV)-Silicon, -Germanium, and -Tin Complexes". Organometallics
1997, 16, 4115-4120.
Levy, C. J.; Puddephatt, R. J. "Rapid Reversible Oxidative
Addition of Group 14 Halide Bonds to Platinum(II): Rates, Equilibria,
and Bond Energies". J. Am. Chem. Soc. 1997, 119, 10127-10136.
Levy, C. J.; Vittal, J. J.; Puddephatt,
R. J. "Synthesis
and Characterization of Group 14-Platinum Complexes". Organometallics,
1996, 15, 2108-2117.
Levy, C. J.; Vittal, J. J.; Puddephatt,
R. J. "Cationic Group
14-Platinum(IV) Complexes". Organometallics 1996, 15, 35-42.
Levy, C. J.; Puddephatt, R. J. "First Experimental Estimation
of a Platinum-Silicon Bond Energy". Organometallics 1995,
14, 5015-5016.
Levy, C. J.; Puddephatt, R. J. "Energy Profile of a Rapid,
Reversible Oxidative Addition Reactionz". J. Chem. Soc., Chem.
Commun. 1995, 2115-2116.
Levy, C. J.; Puddephatt, R. J.; Vittal,
J. J. "The Halogen
Effect in Oxidative Addition of Trimethylsilyl and Trimethyltin
Halides to Platinum(II): Synthesis and Characterization of Silylplatinum(IV)
Complexes". Organometallics 1994, 13, 1559-1560.
Elliot, D. J.; Levy, C. J.; Puddephatt,
R. J.; Holah, D. G.; Hughes, A. N.; Magnuson, V. R.; Moser, I.
M. "A Bridged Cobaltaborane
Complex: First Structural Characterization of a Transition-Metal-BH2
Bond". Inorg. Chem. 1990, 29, 5014-5015. |
