Issue Date: June 15, 2009
Surprise Methyl C–H Activation In DMF
In a synthetic first, California Institute of Technology's Valerie J. Scott, John E. Bercaw, Jay A. Labinger, and coworkers have found that one of the methyl C–H bonds in dimethylformamide (DMF) can be preferentially activated by iridium over the labile aldehyde C–H bond (Organometallics, DOI: 10.1021/om9002413). DMF, (CH3)2NCHO, is a common solvent and widely used as a reagent for introducing carbonyl groups into inorganic and organic molecules. Even so, the mechanism of DMF-based carbonylation reactions is not well-known. The expected carbonylation pathway begins with activation of the aldehyde C–H bond. But when the Caltech team set out to synthesize iridium carbonyl iodide complexes for one of its research projects, the researchers serendipitously found a side reaction in which C–H activation occurred at the methyl end of the molecule, leaving the aldehyde group intact. They observed the C–H switch in the unusual iridium complex shown, which was isolated as a minor product after refluxing IrCl3 with DMF under acidic conditions. "The fact that methyl C–H activation can compete at all with activation of the much more reactive aldehydic C–H bond is unexpected and intriguing," the researchers note.
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