Abstract

We have prepared two novel tethered (arene)Ru(II)/TsDPEN complexes, one containing a p-OTBS on the η6-arene ring, and the other with a p-CO2Et group at the same position, representing an electron-rich and electron-poor derivative. These have been evaluated in asymmetric transfer hydrogenation (ATH) of acetophenone derivatives and acetylcyclohexane. Both catalysts were effective in ATH and gave alcohols in high ees in most cases (with the exception of acetylcyclohexane reduction), mirroring results previously obtained using Ru(II) tethered catalysts. It was notable that the p-CO2Et-containing catalyst was more active than the untethered equivalent catalyst containing an ester on the η6-arene ring, although it still gave products of high ee. This indicates that N-η6-arene ring tethering can compensate for the lower activity of the electron-withdrawing ester group and may be a useful factor to consider for future catalyst design.

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