Solid-phase synthesis of homogeneous ruthenium catalysts on silica for the continuous asymmetric transfer hydrogenation reaction

Overview

Title: 

Solid-phase synthesis of homogeneous ruthenium catalysts on silica for the continuous asymmetric transfer hydrogenation reaction

Abstract: 

The solid-phase synthesis of new asymmetric transfer hydrogenation catalysts as well as the use of these silica supported systems in batch and flow reactors is reported. The ruthenium complex of NH-benzyl-(1R,2S)-(-)-norephedrine covalently tethered to silica showed a high activity and enantioselectivity in the reduction of acetophenone. In three consecutive batchwise catalytic runs, we obtained ee values 88%. In a continuous flow reactor, a very constant catalytic activity was observed; no catalyst deactivation occurred over a period of one week, This has been ascribed to successful site isolation. Using optimized conditions in this flow reactor, the ee was as high as 90% at 95% conversion, The supported catalysts generally show the same trend in catalyst performance as in solution. The viability of our approach was further shown in one example, the ruthenium(II) complex of (1S,2R)-(+)-2-amino-1,2-diphenylethanol, for which an enantiomeric excess of 58% was observed, which is nearly three times higher than its homogeneous analogue.

Authors: 

Albertus J. Sandee, Daniëlle G. I. Petra, Joost N. H. Reek, Paul C. J. Kamer, Piet W. N. M. van Leeuwen

DOI: 

Journal: 

Chemistry-A European Journal

Year: 

2001

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