| The Use of N-heterocyclic Carbenes in Iron Catalyzed Cross Coupling Reactions | Current | Scientists utilize various catalytic pathways to create carbon-carbon bonds. One of these pathways belongs to a group of reactions named iron catalyzed cross coupling reactions. In these reactions, iron bound to ligand is used to form new carbon-carbon bonds by the use of Grignard reagents. These pathways are very similar to those that are palladium, with the exception that they are cheap and less well studied. Because this pathway is catalytic, requires no energy input, and is stable under certain circumstances, it is more environmentally friendly than alternatives, and is recyclable. Because of its ecological implications and lower cost, development of this iron-catalyzed pathway should be studied further. Unfortunately, a suitable ligand has yet to be found which stabilizes this reactive iron (-II) ligand complex while maintaining or maximizing its reactive ability. Evidence suggests that N-Heterocyclic Carbenes, more specifically imidazol-2-ylidene and imidazolin-2-yilidene, could potentially stabilize this complex due to their suspected pi acidity, sigma donating abilities, and variability of their steric bulk. If these carbenes could stabilize the iron ligand complexes mentioned, their applicability would extend much farther than previously anticipated, and numerous industries would be able to reap the rewards of using a catalyst that is reusable, requires no heat input, and is inexpensive. |
| Iron-catalyzed Cross-Coupling Reactions | Current | The ability to form C-C bonds is of paramount importance in organic synthesis. Currently, some of the best synthetic methods for forming C-C bonds use transition metal catalysts. The catalysts most often used employ palladium which is expensive, and has some limitations in the substrate scope. In all of the cross-coupling reactions catalyzed by palladium aryl chlorides are the least reactive of the aryl halides. However, aryl chlorides are more readily available, less expensive, and more stable than the corresponding aryl bromides or iodides, and the development of methods for the use of aryl chlorides in cross coupling reactions would prove very valuable. We are building on some preliminary work done by others which employs iron as a catalyst in the coupling of alkyl Grignards and aryl chlorides. N-heterocyclic carbenes will be employed as ligands in hopes of stabilizing the low valent iron species produced when treated with alkyl Grignard reagents. This should allow for the use of coupling partners other than alkyl Grignards in the cross-coupling reaction with aryl chlorides. Specifically, terminal alkynes will be used in a reaction in a Sonogashira coupling and 1,3-dicarbonyls will be used in a a-arylation reaction. If these reactions are found to proceed as proposed, then the iron carbene catalysts used would prove to be suitable substitutes for palladium-based catalysts. This would make the use of these powerful C-C bond-forming reactions more economically viable for industrial applications. |
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