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Institute for Integrated Catalysis
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Seminar Series Archive

Frontiers in Catalysis Science and Engineering


Jack D. Griffith
Jack D. Griffith, Ph.D.

Jack D. Griffith, Ph.D.
Kenan Distinguished Professor of Microbiology and Immunology and Biochemistry
University of North Carolina School of Medicine
"Electron microscopic visualization of telomeres, DNA repair factors, and nanoparticles bound to cells"
Tuesday, October 23, 2012
EMSL Auditorium - 9:00AM

High-resolution electron microscopy provides a unique window into the architecture of DNA and DNA-protein complexes. In our studies of the ends of chromosomes (telomeres), we have shown that human chromosomes end in giant duplex loops. The telomeric factors and DNA repair factors involved will be described and EM and biochemical studies used to illustrate how these factors are central to both cancer and aging. A new approach using cryo methods combined with freeze drying and high-resolution metal coating is providing an exciting means to visualize cell structures including actin networks and nanoparticles being taken up by cells. The method and applications will be discussed.

Jack R. Norton
Department of Chemistry
Columbia University

"H• Transfer from Transition-Metal Hydrides. Applications to Radical Polymerizations and Cyclizations"
Tuesday, February 14, 2012
EMSL Auditorium - 10:00AM

Steric as well as electronic factors affect the rate at which H• is transferred between a transition metal and the carbon of a double bond.  However, the weak M-H bonds of the first-row metals, particularly vanadium, make them uniquely effective in this regard. 

Such reactions can be used in the catalysis of chain transfer during radical polymerizations.  In this process a metalloradical abstracts H• from a chain-carrying radical, transfers it to the double bond of a monomer, and starts a new chain.  The resting state of traditional cobalt chain-transfer catalysts is the Co(II) metalloradical, but both the metalloradical and the hydride are present during the operation of newer (Cr) catalysts. Success at catalyzing chain transfer requires (1) that the M-H bond not be too much stronger than the 50 kcal/mol C-H bond in chain-carrying radicals, and (2) that M• be stable enough to discourage the formation of bonds other than that to hydrogen. 

CpCr(CO)3H and HV(CO)4(P-P) can be used to initiate radical cyclizations by transferring H• to activated terminal olefins. However, the resulting radicals must cyclize quickly; competing reactions include transfer of a second H• (resulting in hydrogenation) and removal of an H• (resulting in isomerization).  Cp(CO)3CrH is relatively slow at H• transfer, but can be regenerated with H2 gas, enabling it to carry out reductive cyclizations catalytically; vanadium hydrides HV(CO)4(P-P) are faster but operate stoichiometrically.

Douglas W. Stephan
Department of Chemistry
University of Toronto

"Frustrated Lewis Pairs": Metal-Free Hydrogenations and Small Molecule Activation
Thursday January 26, 2012
EMSL 1077 - 1:00PM


The activation of hydrogen has been the purvue of transition metals for 100 years. In recent work we have discovered the first metal-free system capable of H2 activation. Sterically encumbered Lewis acid and base combinations do not form "classical" Lewis acid-base adducts. Rather, the unquenched Lewis acidity and basicity of such sterically "frustrated Lewis pairs (FLPs)" is available for reactivity. Such systems have been shown to effect the heterolytic cleavage of hydrogen and applied to develop metal-free hydrogenations for C=N bonds in a variety of organic substrates. In addition, we have shown that FLP hydrogenation can be used to effect aromatic reductions. FLPs are also shown to exhibit unprecedented reactivity with a variety of other small molecules, including olefins, dienes, alkynes, cyclopropanes, CO2 and N2O. The implications of the discovery of such systems to catalysis and further details will be presented in this lecture.

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