CHEMISTRY: Reduced by the Main Group

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Science  07 Sep 2007:
Vol. 317, Issue 5843, pp. 1295b
DOI: 10.1126/science.317.5843.1295b

The addition of H2 across C=O and C=N multiple bonds has tended to require help from transition metals to coax the process along by first slicing through the bond connecting the two H atoms. An unusual metal-free complex, composed of phosphorus and boron centers bridged by a fluorinated phenyl ring, was recently also shown to reversibly cleave H2—ostensibly by proton addition to P and hydride transfer to B. Chase et al. have now found that, like transition metal complexes, this main group compound acts as an effective catalyst for hydrogenation of CN bonds in aziridines and sterically encumbered imines. The reaction is fastest when electron-donating substituents raise the basicity of the imine nitrogen, implicating a mechanism involving initial proton transfer from the P center. Nitriles and less bulky imines blocked catalysis by coordinating tightly to the B center but could be induced to react through protection by an external coordinating borane. — JSY

Angew. Chem. Int. Ed. 46, 10.1002/anie.200702908 (2007).

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