Homogeneous hydrogenation of fluoroaromatic imines with Ni compounds, evidence for η2-C=N intermediate in the catalytic cycle

The catalytic hydrogenation of a series of fluorinated imines with [Ni(dippe)(mu-H)](2) dippe = 1,2 bis(diisopropylphosphino)ethane was undertaken and the effect of solvent, temperature, and hydrogen pressure on reactivity assessed. High conversions of fluorinated imines into amines were obtained in methanol, under relatively mild temperature and pressure conditions; a transfer hydrogenation process was found to take place in situ, when using nickel catalysts. The use of H-2 pressure was therefore required to drive reactions to completion. In particular, electron poor imines were hydrogenated at a faster rate than the electron-rich ones. A mechanistic proposal involving a pi-coordinated imine as a key intermediate is presented. (C) 2008 Elsevier B.V. All rights reserved.