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High-Spin Cobalt Hydrides for Catalysis

Description: Organometallic chemists have traditionally used catalysts with strong-field ligands that give low-spin complexes. However, complexes with a weak ligand field have weaker bonds and lower barriers to geometric changes, suggesting that they may lead to more rapid catalytic reactions. Developing our understanding of high-spin complexes requires the use of a broader range of spectroscopic techniques, but has the promise of changing the mechanism and/or selectivity of known catalytic reactions. These changes may enable the more efficient utilization of chemical resources. A special advantage of cobalt and iron catalysts is that the metals are more abundant and cheaper than those currently used for major industrial processes that convert unsaturated organic molecules and biofeedstocks into useful chemicals. This project specifically evaluated the potential of high-spin cobalt complexes for small-molecule reactions for bond rearrangement and cleavage reactions relevant to hydrocarbon transformations. We have learned that many of these reactions proceed through crossing to different spin states: for example, high-spin complexes can flip one electron spin to access a lower-energy reaction pathway for beta-hydride elimination. This reaction enables new, selective olefin isomerization catalysis. The high-spin cobalt complexes also cleave the C-O bond of CO2 and the C-F bonds of fluoroarenes. In each case, the detailed mechanism of the reaction has been determined. Importantly, we have discovered that the cobalt catalysts described here give distinctive selectivities that are better than known catalysts. These selectivities come from a synergy between supporting ligand design and electronic control of the spin-state crossing in the reactions.
Date: August 29, 2013
Creator: Holland, Patrick L.
Item Type: Report
Partner: UNT Libraries Government Documents Department

Selectivity and Mechanism of Hydrogen Atom Transfer by an Isolable Imidoiron (III) Complex

Description: This article discusses a mechanistic study of hydrogen atom transfer by an isolable iron (III) imido complex, LᴹᵉFeNAd (Lᴹᵉ = bulky β-diketiminate ligand, 2,4-bis(2,6-diisopropylphenylimido)pentyl; Ad = 1-adamantyl).
Date: May 12, 2011
Creator: Cowley, Ryan E.; Eckert, Nathan A.; Vaddadi, Sridhar; Figg, Travis M.; Cundari, Thomas R., 1964- & Holland, Patrick L.
Item Type: Article
Partner: UNT College of Arts and Sciences

Studies of Low-Coordinate Iron Dinitrogen Complexes

Description: This article discusses low-coordinate iron dinitrogen complexes. Understanding the interaction of N₂ with iron is relevant to the iron catalyst used in the Haber process and to possible roles of the FeMoco active site of nitrogenase.
Date: December 31, 2005
Creator: Smith, Jeremy M.; Sadique, Azwana R.; Cundari, Thomas R., 1964-; Rodgers, Kenton R.; Lukat-Rodgers, Gudrun; Lachicotte, Rene J. et al.
Item Type: Article
Partner: UNT College of Arts and Sciences

Cobalt-Dinitrogen Complexes with Weakened N-N Bonds

Description: Article discussing research on cobalt-dinitrogen complexes with weakened N-N bonds.
Date: June 19, 2009
Creator: Ding, Keying; Pierpont, Aaron W.; Brennessel, William W.; Lukat-Rodgers, Gudrun; Rodgers, Kenton R.; Cundari, Thomas R., 1964- et al.
Item Type: Article
Partner: UNT College of Arts and Sciences

The Reactivity Patterns of Low-Coordinate Iron-Hydride Complexes

Description: This article discusses the reactivity patterns of low-coordinate iron-hydride complexes. The authors report a survey of the reactivity of the first isolable iron-hydride complexes with a coordiination number less than 5.
Date: April 30, 2008
Creator: Yu, Ying; Sadique, Azwana R.; Smith, Jeremy M.; Dugan, Thomas R.; Cowley, Ryan E.; Brennessel, William W. et al.
Item Type: Article
Partner: UNT College of Arts and Sciences