Biomimetic Catalysis with Immobilised Organometallic Ruthenium(II) Complexes: Substrate and Regioselective Transfer Hydrogenation of Ketones
Chloro-(h6-arene) complexes of Ru(II) with N-sulfonyl-1,2-ethylenediamine ligands that have one or two styrene side chains were synthesized and characterized. The chloro ligand was substituted with a diphenylphosphinato ligand and the resulting organometallic complexes are transition state analogs for the Ru-catalyzed transfer hydrogenation of benzophenone. Following the protocol of mol. imprinting, these complexes were copolymd. with ethylene glycol dimethacrylate (EGDMA) in the presence of a porogen. The polymers were ground and sieved, and the phosphinato ligand was substituted with a chloro ligand, thus generating a shape-selective cavity in close proximity to the catalytically active metal center. When tested for their ability to catalyze the redn. of benzophenone, the imprinted polymers showed a significantly higher activity (up to a factor of seven) than control polymers without cavities. Out of a mixt. of seven different arom. and aliph. ketones, benzophenone was preferentially reduced when the imprinted polymer was used. Also, the specificity of the catalyst for diaryl ketones was confirmed in a reaction with a bifunctional substrate, 4-acetyl-benzophenone; the diaryl ketone was reduced faster with the imprinted catalyst than the acetyl group. The opposite regioselectivity was obsd. with the control polymer. Both the activity and the selectivity of the imprinted catalysts are dependent on how the Ru complexes are attached to the polymer backbone. A double connection proved to give superior results.
Record created on 2006-02-13, modified on 2016-08-08