Issue Date: July 21, 2008
Novel Radical Hydrogen Donors may be Less Toxic
A new class of hydrogen-atom donor reagents may be less toxic and therefore could have wider applicability than the trialkyltin reagents commonly used for radical reactions. Trialkyltin hydrides are stable, but their hydrogen atoms can dissociate easily, leading to these organotin reagents' frequent use as hydrogen donors in radical deoxygenations and other radical reactions. But the reagents are also neurotoxins and are difficult to remove from reaction products, making them inappropriate for use in syntheses of medicines and other products. Now, Louis Fensterbank, Emmanuel Lacôte, and Max Malacria of the University of Pierre & Marie Curie, in Paris; Dennis P. Curran of the University of Pittsburgh; and coworkers find that complexes of N-heterocyclic carbenes (NHCs) with borane (such as the one shown, Ph = phenyl) have easily dissociable hydrogens and the requisite stability to serve as effective radical hydrogen donors (J. Am. Chem. Soc., DOI: 10.1021/ja804150k). But they contain no metals or heavy elements and so may be less toxic than trialkyltins. The researchers are currently investigating ways in which the NHC-borane reagents can be modified and the synthetic scope of radical reactions in which they can participate.
- Chemical & Engineering News
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