Solid-Phase Synthesis of Homogeneous Ruthenium Catalysts on Silica for the Continuous Asymmetric Transfer Hydrogenation Reaction
✍ Scribed by Albertus J. Sandee; Daniëlle G. I. Petra; Joost N. H. Reek; Paul C. J. Kamer; Piet W. N. M. van Leeuwen
- Publisher
- John Wiley and Sons
- Year
- 2001
- Tongue
- English
- Weight
- 130 KB
- Volume
- 7
- Category
- Article
- ISSN
- 0947-6539
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✦ Synopsis
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)-(À)-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 of 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.