Molybdenum Tris-Dithiolene: Synthesis and Study

Posted May 26th, 2010 at 3:06 pm.

Cara Blankenbicker

Mentor: Dr. Sharon Burgmayer

Molybdenum dithiolene complexes are a vital area of research as they shed light on the catalytic activities of the molybdenum cofactor, a species present in molybdenum enzymes that is responsible for electron transfer reactions. While attempting to synthesize a molecular model of the molybdenum cofactor using a molybdenum diothiolene compound, a tris-dithiolene molybdenum complex was discovered that possessed unexpected magnectic and structural properties. It is these characteristics that will be the subject of my summer research - a continuation of the thesis work of Laura Snyder.

The tris-dithiolene compounds are identifiable by the presence of three dithiolene ligands, each of which contains two sulfur atoms that chelate to the molybdenum center. Although the compound has not yet been crystallized, it is known from other research that the complex possesses trigonal prismatic geometry. While most related tris-dithiolene compounds are diamagnetic, the Mo complex synthesized was found to be paramagnetic - a property that was completely unexpected as Crystal Field Theory predicts a diamagnetic character. It is hoped that by synthesizing other tris-dithiolene derivates it will be possible to determine what aspect of these ligands results in the unusual magnetic properties.

Currently, four ligands are being used in this research - diFEQ, PEQO, NEQO, and FEQO. All these substituents are synthesiszed from the same 2-chloroquinoxaline, but contain different alkynes, - 1-ethynyl-2,4-difluorobenzene, phenylacetylyne, naphthalene acetylyne and 1-ethynyl-2-fluorobenzene, respectively. Each complex has yielded results that imply hyper-paramagnetic character, or 4 to 5 unpaired electrons for the Mo IV . By using different alkynes we hope to increase the variety of data to help understand this phenomenon.

The goals for this summer are to first learn to synthesize the precursors of the molybdenum complexes, then the complexes themselves while maintaining or improving upon the yields. I will also be compiling and analyzing data from sources such as magnetic susceptibility analysis, mass spectrometry and UV/vis spectroscopy. Finally, I hope to find another alkyne to add to the variety of tris-dithiolenes already under observation.

Filed under: 2004,Blankenbicker, Cara,Burgmayer, Dr. Sharon by Ann Dixon

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