Development of Rhodium N-heterocyclic Carbene Complexes for C-H Activation

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Authors
Walker, Roxanne L.
Issue Date
2010
Type
Thesis
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en_US
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Abstract
Depleting deposits of petroleum are the source of 60% of the carbon used by the chemical industry. Methane, the main component of natural gas, is a possible alternative source of carbon. The high energy costs of synthesizing methane through syngas could be reduced by finding a more efficient method to convert it to methanol. An optimal process might use a catalyst to activate one C-H bond of methane, lowering the activation energy of the conversion. We duplicate the synthesis of two CNC (CNC = 3,3’-diaryl-1,1’- pyridine-2,6-diyl-bis(imidazol-2-ylidene)) compounds. When coordinated to rhodium, these complexes are strong candidates for catalytic activation of C-H bonds of alkanes. The intended final products are [3,3’-Bis(R)-1,1’-pyridine-2,6-diylbis(imidazol-2- ylidene)]chlororhodium(I) where R={t-butyl, n-butyl}. The precursor t-butyl imidazole was synthesized from t-butyl amine (acidified in water to pH = 2 with phosphoric acid), glyoxal and formaldehyde. Neat reaction of t-butyl imidazole with 2,6-dibromopyridine in a flame-sealed ampoule for 72 h at 130 °C gave [3,3’-Bis(t-butyl)-1,1’-pyridine-2,6- diylbis(imidazol-2-ylidene)]. Similar reaction using stock n-butyl imidazole for 20 h at 150 °C gave [3,3’-Bis(n-butyl)-1,1’-pyridine-2,6-diylbis(imidazol-2-ylidene)]. The tbutyl complex was deprotonated using potassium bis-trimethylsilylamide in THF. The deprotonated form did not complex to Rh using [Rh(C2H4)2Cl]2 or [Rh(COE)2Cl]2. The nbutyl complex was not deprotonated by potassium bis-trimethylsilylamide or triethylamine. Once these ligands are fully synthesized and characterized, their reactivity and ability to activate C-H bonds will be explored.
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ix, 26 p.
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Kalamazoo College
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U.S. copyright laws protect this material. Commercial use or distribution of this material is not permitted without prior written permission of the copyright holder. All rights reserved.
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