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

The catalytic hydrogenation of a series of fluorinated imines with [Ni(dippe)(μ-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 H2 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 π-coordinated imine as a key intermediate is presented.

The hydrogenation of fluorinated imines with Ni compounds was achieved. High conversions to their corresponding amines were obtained using polar donor solvents such as methanol. Although transfer hydrogenation of imines is observed, H2 pressure is needed to drive the reaction to completion. Evidences for the η2-CN coordination as a first step of a catalytic cycle is presented.Figure optionsDownload as PowerPoint slide